Comprehensive overview of microwave technology research projects currently being investigated by European academic institutions and commercial organizations
Microwave Journal European Editor
A commitment to well funded, focused, commercially viable research is critical to the future prosperity of the microwave industry. In this special report Microwave Journal takes a snapshot of the research projects being investigated by academic and commercial establishments across Europe to discover the innovations that will dictate the shape of tomorrow's European and global microwave technology.
The call for miniaturization and the move towards higher frequencies for wireless applications are critical trends influencing the direction of microwave component/system development. The current cycle sees radio frequency (RF) and microwave engineering having grown rapidly in importance in recent years, stimulated in particular by booming digital mobile communications. A host of other wireless-based applications are also experiencing rapid expansion, ranging from radio-based Local Area Networks (LANs), through Local Multipoint Distribution Systems (LMDS), Global Positioning Systems (GPS), Microwave Video Distribution Systems (MVDS), anti-collision systems for automobiles and so on. The next few years are also expected to see the introduction of third generation mobile communications (UMTS/ IMT2000) offering many new features including user data rates up to 2 Mb/s.
These newer applications join many well-established uses of RF and microwaves in the approximate frequency range 300 MHz to 300 GHz, including terrestrial and satellite-based communications, radar, heating, radio astronomy, medical therapy and diagnostics, etc. At the same time, microwave engineering techniques are assuming increasing importance in high speed digital electronics as clock frequencies move into the 1 GHz range, as well as in optoelectronics, with data rates exceeding 40 Gb/s.
Using the Guide
All of these fields are developing through research and this supplement aims to highlight some of the current projects under investigation across Europe. The listing is by country within each section. All relevant microwave research at the time of this writing is included but the guide is not all encompassing. Instead it will develop on a year-by-year basis. Each entry has a short profile of current research activity and contact details.
The guide includes a diversity of work ranging from materials development, through broadband wireless systems, to military, satellite and space applications. The geographical coverage aims to be varied with the inclusion of former Eastern block countries being significant. Here greater commercial freedom and openness has provided access to commercial funding and wider potential markets, together with the opportunity for broader collaboration. Pan-European projects are also highlighted, whilst commercial confidentiality and the slump in the telecoms industry have limited the number of commercial test houses included to a select few.
Universities and Academic Institutes
Featured in alphabetical order by country the following entries for each university name the departments involved in microwave research, cover the extent of the work currently ongoing, outline the key areas of research, provide contact details and in some cases focus on a project of particular significance.
Technical University of Vienna
Research carried out in association with Infineon Technologies in Munich, Germany.
In the field of RF circuit development there has been close cooperation between the university's Institute of Communications and Radio Frequency Engineering, headed by Professor A.L. Scholtz, and Infineon Technologies' Corporate Research, for about 12 years.
The research work is focused on monolithic integration of circuits for analog, digital and mixed analog/digital circuits for communications applications, including MMDS from 2.1 to 2.7 GHz, WLANs at 2.4 and 5.2 GHz and satellite communications from 8.2 to 12.4 GHz. The trend to higher carrier frequencies for wireless applications such as point-to-multipoint systems at 10 GHz and between 24.5 GHz and 29.5 GHz, LMDS at 28 GHz and 38 GHz, and MVDS at 42 GHz raises the demand for LNAs, mixers, frequency multipliers and dividers, VCOs, synthesizers, etc., suitable for frequencies in the range mentioned.
SiGe bipolar technology is the most attractive candidate for the emerging field of broadband wireless services. It combines the potential to fulfill the technical specifications with the cost advantages, integration and manufacturing capabilities of standard silicon technologies.
Key Areas of Research
The circuits are chosen for demonstrating low noise, lowest power consumption or high bandwidth for the applications mentioned above. Significant results that have already been published for wireless applications based on silicon technologies include a dual-modulus prescaler in SiGe bipolar technology which has been optimized for low power applications with the result that the circuit consumes only 4.4 mW from a 2.3 V supply operating up to 4.7 GHz.
Investigations into the noise characteristic of LNAs in silicon and SiGe bipolar technologies has seen the development of silicon devices that achieve a low noise figure of 2.8 dB at 9.5 GHz and a gain of 21 dB. At 10.5 GHz a low noise figure of only 2 dB and a gain of 26 dB has been achieved for SiGe devices.
A silicon broadband mixer with 3 dB bandwidth of 17 GHz and gain higher than 5.4 dB offers a low DSB noise figure smaller than 8.8 dB and a low power consumption of 7 mW, whilst broadband mixers realized in SiGe bipolar technology offer a 3 dB bandwidth of 20 GHz and gain higher than 10 dB. The DSB noise figure is 6 dB and the power consumption is 10 mW.
Also, a highly integrated mixed analog/digital circuit is demonstrated in standard silicon production technology. The phase-locked loop frequency synthesizer offers an output frequency range between 6.40 and 6.75 GHz, and the circuit consumes only 82 mW from a 3 V supply.
Proposals are for a method for designing monolithic lumped planar transformers where a lumped low order equivalent model is derived from the physical layout using a new expression for the substrate loss. Two transformers have been considered in detail, showing excellent agreement between simulation and measurement results up to 20 GHz.
A key project is the investigation of different concepts of active mixers for up and/or downconversion. The circuits are being developed for broadband applications like point-to-multipoint systems up to 30 GHz, LMDS at 28 and 38 GHz or MVDS at 42 GHz. The use of matching networks and optimization compromises between bandwidth, noise figure, gain and power consumption are part of the work.
Benefits of SiGe mixers over silicon mixers such as the lower transmit time of SiGe are being considered and related to the relevant technology parameters. Also, careful circuit design in combination with recent advantages in Infineon's silicon-based bipolar technologies offer new opportunities for further optimization.
The excellent results for circuits like LNAs, mixers, VCOs, etc., allow for integration of complete RF subsystems.
(Heads of Department)
Professor Arpad L. Scholtz, Technical University of Vienna, Institute of Communications and Radio Frequency Engineering, Gusshausstrasse 25/389, A-1040 Vienna, Austria; Sabine Hackl, Infineon Technologies AG, Corporate Research, High Frequency Circuits, Otto-Hahn-Ring 6, D-81730 Munich, Germany.
Helsinki University of Technology (HUT)
The Department of Electrical and Communications Engineering (ECE) is the largest at Helsinki University of Technology. The department's Radio Laboratory and the Signal Processing Laboratory have formed a research unit entitled the Smart and Novel Radios (SMARAD) research unit aiming at world-class research in radio engineering and related signal processing in radio transceivers. Its leader is Professor Antti RŠisŠnen from the Radio Laboratory, whilst Professor Pertti Vainikainen and Professor Sergei Tretyakov from the Radio Laboratory, as well as Professor Timo Laakso and Professor Visa Koivunen from the Signal Processing Laboratory, are the other principal investigators in SMARAD.
The Radio Laboratory was established in 1924 in the Department of Mechanical Engineering but has been part of the ECE since it was founded in 1941. It belongs to the research area of Radio Science together with the Electromagnetics Laboratory, Laboratory of Space Technology and MetsŠhovi Radio Research Station. Furthermore, the Radio Laboratory is involved in the Millimeter Wave Laboratory (MilliLab) of Finland, which has the status of External Laboratory of the European Space Agency (ESA). MilliLab is a joint research institute between HUT and VTT (Technical Research Center of Finland). All these faculties are active members of the IDC (Institute of Digital Communications) and are co-operating in radio and communications engineering related projects.
Key Areas of Research
SMARAD undertakes RF, microwave and millimeter-wave as well as communications signal processing research and education. Key areas are research into RF techniques for wireless communications (including wideband propagation in mobile systems), radio channel modeling and measuring, smart (adaptive) antennas, receiver structures and architectures, and communication signal processing. The scope of the signal processing research is in developing theory and algorithms for smart, adaptive antenna systems and designing advanced and flexible transceiver structures for future wireless communication systems.
A fully novel approach is taken. For instance, in antenna measurements a radio hologram is used as the collimating element in order to form the necessary planar wave front in a compact antenna test range (CATR). Novel ideas are also applied in the design of new antenna structures resulting in several patents and patent applications. SMARAD also supports the telecommunications industry by bringing new state-of-the-art results to it.
As a center of excellence in research SMARAD has a well-established network of co-operating partners in industry, research institutes and academia worldwide. Its funding sources are also diverse, and include the Academy of Finland, Tekes (the Finnish National Technology Agency) and industry, whilst IDC serves as an umbrella organization for most of the telecommunication projects.
Under the leadership of Professor Sergei Tretyakov, the Radio Laboratory has started research on advanced artificial materials and smart structures such as composite materials for absorbers and conformal antennas.
Professor Antti RŠisŠnen, Helsinki University of Technology, Radio Laboratory, PO Box 3000, FIN-02015 HUT, Finland. Tel: +358 9 451 2241; e-mail: firstname.lastname@example.org.
University of Lille
Professor Georges Salmer heads the Institut d'Electronique et de Microélectronique du Nord (IEMN). It comprises three departments including the Département Hyperfréquences et Semiconducteurs (Devices and Microwave Department), headed by Professor Paul Alain Rolland.
The principal branches of research undertaken at IEMN include work on modern electronics, innovative materials, microelectronics, microwaves, optoelectronics, electromagnetics, acoustics, ultrasound, microsystems, sensors and instrumentation. The Department was founded in 1992 and is the result of the fusion of three laboratories: the High Frequency and Semiconductors Center, the Laboratory of Optoacoustic Electronics, and the Laboratory of Studies on Surfaces and Interfaces. The former is where the majority of microwave research is carried out.
Key Areas of Research
Recent research into electronic devices and microwaves includes: a simulation study which not only considered the physical behavior of field effect transistors but also attempted to give realistic performance predictions and derive optimization rules; the design, realization and characterization of heterostructure FETs using new materials and/or new topologies, with applications for high gain/low noise, mm-wave circuits; and the design, fabrication and RF assessment of electronic nonlinear systems for the up and downconversion of RF signals in the 100 GHz to 1THz frequency range.
In the field of research into microelectronics circuits for RF to mm-wave frequencies the aim of a recent project was to design and realize original circuits and subsystems for emerging applications such as passive imaging systems, CW/A radars, high data rate telecommunication networks, smart microsystems, etc. Specifics were to investigate new mounting and assembly techniques for compact MMIC subsystems and to validate emerging technologies.
Medical microwave research undertaken encompasses the design, realization, modeling and testing of antennas, applicators and sensors to be used in hyperthermia and thermotherapy systems controlled with microwave radiometry.
To investigate, design and realize mm-wave (40 and 60 GHz) short range, high data rate wireless communication systems interconnected with optical fiber networks to cover the last mile of the installation (indoor and outdoor applications) IEMN is working on a high data rate (155 Mb/s) indoor communication network based on a composite fiber-radio link at 60 GHz.
In order to optimize the trade-off between data rate and bit error rate (BER), system simulations have been carried out that take into account the 60 GHz radio channel characteristics, the nonlinearities of the various mm-wave devices and local oscillators. These simulations have allowed the team to optimize both the antennas and the modulation scheme for such indoor communication where multipath propagation is dominant. This work is still in progress mainly to improve the 60 GHz channel and to reach a 155 Mb/s data rate with a BER lower than 10-5 .
Professor Paul Alain Rolland, Département Hyperfréquences et Semiconducteurs, Institut d'Electronique et de Microélectronique du Nord. E-mail:Paul-Alain.Rolland@ IEMN.Univ-Lille1.fr.
University of Bremen
Professor Fritz Arndt heads the Microwave Department.
Work in the field of fast mode-matching (MM) CAD and optimization methods for satellite and wireless communication components began over twenty years ago with the development of MM CAD procedures for waveguide discontinuities and filters. Component CAD examples include filters without tuning screws, compact diplexers, multiplexers, power dividers, stub-loaded phase shifters, ortho-mode transducers (OMT) for space applications, all kinds of waveguide couplers, polarizers and complete feed networks.
In the 1980s new and pioneering contributions of the research group included MM-based optimization of metal insert and iris coupled waveguide filters, numerical electromagnetics (EM)-based optimization of waveguide transformers, couplers and polarizers, EM-based 3D analysis of shielded dielectric image guides and MM CAD of waveguide diplexers. In the 1990s contributions included the MM calculation of the magic-tee, six-port cross, MM techniques applied for waveguide discontinuities in elliptical coordinates and a boundary MM technique for the CAD of post coupled filters.
Detailed investigation of advanced method-of-moment (MoM) techniques for various antennas has been ongoing. At present, most of the research activities are devoted to the rigorous analysis and optimization of slot arrays, including inner and outer coupling effects, and on aperture coupled large microstrip patch arrays.
When considering new finite-difference (FD) frequency-domain and time-domain (TD) techniques for the CAD of general microwave components and antennas the research group has developed original and pioneering contributions. Recently, a general FD-TD CAD tool has been developed with optimizers for the design of general 3D microwave structures, such as dielectric resonator filters, input multiplexers (IMUX) and complex antenna structures (also with radomes).
Recent activities include finite element method (FEM) techniques in spherical coordinates for efficient models for radiating structures taking the outer geometry into account, and for spherical multimode cavities. Also, employing hybrid MM/boundary contour (BC) MM techniques the research group published the first hybrid MM/BCMM technique for the fast and flexible CAD of mitered bends, Y-junctions and post compensated waveguide junctions.
Key Areas of Research
Efforts have been targeted at the development of efficient hybrid MM/FE and MM/FD CAD techniques for the design and optimization of waveguide components. The developed hybrid MM/FE technique introduced in 1994 combines the advantages of the efficiency of the MM method with the flexibility of the FE solver. The 2D eigenvalue problem of general waveguide cross-sections is solved by a 2D FE method, whilst the step discontinuities are calculated by the MM technique. The research group has also published the first papers on the successful CAD and optimization of dual-mode filters, ridged waveguide and waffle iron filters using the advanced MM/FE method.
Current investigations concentrate on the inclusion of radiating structures (horns, coupled horns, slots), the optimization of eight-pole dual-mode filters and multiplexers. An efficient MM/FD method for the CAD and optimization of comb-line filters has recently been developed.
In the field of efficient MoM and hybrid MM/MoM techniques a fast SDA technique has been developed for the CAD of large finite arrays of patch antennas with a high number of elements. The current focus is on the genetic algorithm optimization of aperture coupled large microstrip patch arrays and on reflect arrays. Other significant work includes: the development of a novel space domain MPIE; a new MLFMM analysis of horn antennas; a new hybrid MM/FE/ MoM technique for the rigorous analysis of arbitrarily shaped horn antennas including the outer geometry; and a novel GSM/MoM technique for the CAD of waffle-iron filters with round teeth.
Twenty years of research experience and cooperation between the University of Bremen and the Microwave Innovation Group (MIG) has seen the development of the commercially available WASP-NET," a hybrid MM/FE/FD/MoM CAD software package.
Based on research experience in numerical electromagnetics (EM), in particular in MM, FE, FD, MoM and related hybrid techniques, the software package has been created for the robust, fast and rigorous CAD, and optimization of all kinds of waveguide components and networks to solve tough real-world design problems in realistic time dimensions. A hybrid numerical electromagnetics (EM)-based CAD and optimization tool, WASP-Net unites the CPU speed of the semi-analytical mode-matching (MM) method with the flexibility of the space-discretization-based FE/FD/ MoM techniques.
Professor Fritz Arndt, PO Box 33 04 40, D-28334 Bremen, Germany. Tel: +49 421 218 2495/2700; e-mail: email@example.com.
Universität Karlsruhe (Karlsruhe University)
The Institut für Höchstfrequenztechnik und Elektronik (Department of High Frequency and Electronics) is headed by Professor Werner Wiesbeck.
Under development are wave propagation software and network planning tools for GSM and UMTS for both outdoor and indoor scenarios, and the modeling of dynamic MIMO channel assignment is currently being carried out.
Various activities are being investigated under the heading of Antennas, Radar Techniques and Sensors. In the field of antennas, several computation algorithms and design programs, especially for planar and conformal antennas, have been developed. Dual-polarized multi-band basestation antennas are designed for future cellular mobile communication systems to allow multi-standard operation in different frequency bands. Radar systems for anti-personal mine detection are currently in test. Air-borne Synthetic Aperture Radar (SAR) systems with high resolution have recently been built and successfully tested. In the growing field of microwave sensors, millimeter-wave frequencies offer new potential for various applications. High end automotive sensors are also currently being developed.
In the field of electromagnetic compatibility (EMC) numerical simulation tools for the design of EMC-chambers are under development, whilst new limiting values for mobile phone basestations require further research concerning EMC with regards to the environment. In the medical sphere numerical simulation software for predictions of nonlinear ultrasound propagation, attenuation and heating in human tissue has been written and is currently being extended to take into account bubble dynamics. Simulation and optimization of high power ultrasound devices for therapeutic purposes and the measurement of high power ultrasound in vitro and in vivo are also under investigation.
Key Areas of Research
A very accurate modeling method for wave propagations in tunnels, which is applicable to mobile phone network design, has been developed. Also, an efficient numerical algorithm for the design of conformal antennas on cylindrical surfaces has been produced with the result that test antennas have been built and the design was verified successfully.
In the field of broadband basestation antennas a dual-polarized stacked patch antenna array has been designed and built using microstrip technology. The antenna covers GSM1800, DECT and UMTS frequency bands. For use on board helicopters a forward-looking synthetic aperture radar with digital beam forming on receive only has been built. In the automotive domain mm-wave sensors for various applications in cars is currently being developed.
An applicator for the processing of nanostructures based on zeolites has recently been produced, in which the temperature profiles are adjustable within the applicator. Finally, the research group developing medical diagnostic techniques is nearing completion of simulation software to predict therapeutic relevant ultrasound and temperature field parameters for lithotripsy and non-invasive thermotherapy of tumors.
Reflecting the diversity of research undertaken at UniversitŠt Karlsruhe is the development of a new wave-wave sensor for automotive, railway and manufacturing monitoring. The aim is to develop a sensor capable of speed measurement in cars, detecting the motion of the wheels, increasing train safety and also monitoring wear and tear. The sensor will operate in the mm-wave range.
Based on the radar principle the sensor detects reflected signals from the object and delivers baseband signals that can be evaluated in order to obtain the desired information. For the first time, fabrication will involve a combination of the mechanically very stable low temperature co-fired ceramic (LTCC) substrate into which a GaAs-chip will be integrated. The LTCC hosts the antenna and DC-electronics and the GaAs-chip will be bonded onto the LTCC.
The key finding of the project has been the possibility of detecting motion and thickness with focused millimeter-waves. Probable commercial applications include the speed detection of cars, the replacement of any kind of wheel sensor such as ABS, the surveillance of the state of steel wheels on trains, and the monitoring of the wear and tear of manufacturing machines. At present there is the possibility of commercial collaboration with Siemens Munich, UMS Semiconductor and various car manufacturers.
The first publication of a paper on this subject entitled "Multipurpose 76.5 GHz Near Field Radar Sensor" by Y. Venot and W. Wiesbeck will be delivered at EuMC 2001 in London in September.
UMTS-basestation components, including dual-polarized multi-band antennas, power amplifiers and other equipment, will be developed. Scenarios for ad-hoc networks in traffic and other mobile applications will be investigated together with solution proposals for handling MIMO-problems among these ad-hoc networks. Highly sophisticated microwave heating equipment (also for space applications) will be developed and built, and EMC-aspects will be covered. Future projects will include the study of broadband antennas, the development of a portable anti-personnel mine detection system and the simulation and optimization of therapeutic ultrasound devices.
Professor Werner Wiesbeck, Institut für Höchstfrequenztechnik und Elektronik, Universität Karlsruhe, Kaiserstrasse 12, Karlsruhe, Germany. Tel: +49 721 608 2522; e-mail: Werner Wiesbeck@etec.uni-karlsruhe.de.
Budapest University of Technology and Economics (BUTE)
The Department of Microwave Telecommunication is headed by Professor Zombory László.
The wide range of research undertaken covers the subject areas of antennas and radiowave propagation, space research, electromagnetic compatibility, high speed technology, software radio, optical devices, and mobile and microwave communication.
Key Areas of Research
In the field of antennas and radiowave propagation the major effort is toward the numerical calculation of electromagnetic fields, and the development of antennas for various purposes, including the communications applications of microstrip antennas and the research of low loss materials. The radiowave propagation research includes the development of digital terrain models, and for the optimization of basestation-sites for indoor and outdoor applications.
The space research is done in the Space Research Group that was originally formed by the Hungarian Academy of Sciences and National Space Research Bureau. In the framework of the INTERCOSMOS international cooperation, data-collection, power supply and telemetry transceiver systems have been developed.
The EMC laboratory is devoted to electromagnetic compatibility measurements and compliance tests, and operates an anechoic test chamber with power-mains filtering, as well as having an open-site measuring facility. The High Speed Technology team deals with signal-integrity issues in high speed digital systems, such as cross talk, simultaneous switching noise and signal distortion in printed-circuit-board and multi-pin connector interconnects, as well as in advanced electrical and optical busses.
Under the topic of software radio microwave research and development is conducted in the applications of planar microwave substrates. Several devices and circuits as well as simulation software have been developed for weather-satellite receiver stations, microwave TV sets and spread-spectrum radio equipment.
In the field of optical communications, the department does research and development on the physical layer. Optoelectronic devices and optical-RF transducers are also investigated. Modulation, wave-propagation and coding issues are covered in the main topic area of mobile communications.
The department is involved in various ongoing international projects. In the photonic devices domain they include developing techniques for modeling and measuring advanced photonic telecommunication components related to the dynamic behavior of photonic devices, studying semiconductor devices for optical signal processing and investigating wavelength scale photonic components for telecommunications.
Radiowave propagation projects cover radiowave propagation effects on next-generation fixed-service terrestrial telecommunication systems and radiowave propagation modeling for new Satcom services at Ku-Band and above. In the telecommunication processing field ongoing studies include digital signal processing application in communications and intelligent processing for communication terminals.
Professor Zombory László, Budapest University of Technology and Economics, Mûegyetem rkp. 3-9, H-1111 Budapest, Hungary. Tel: +36 1 463 1111; e-mail: firstname.lastname@example.org.
University College Cork (UCC)
The Centre Director of the Electrical and Electronic Engineering (Teltec Ireland) Department is Professor Patrick J. Murphy.
RF/microwave engineering research has been ongoing since the 1960s. In the mid 1980s, a number of government-sponsored programs to facilitate the transfer of advanced technologies from Irish universities to industry were initiated. Within the context of the program dealing with telecommunications technologies (Teltec Ireland), UCC was nominated as the national center of expertise in RF/microwave engineering.
Funding in excess of 2 million Euros has been made available to equip the laboratory with the most modern test and CAD equipment. Accordingly, a substantial amount of industry commissioned research and development work has been carried out over a period of almost fifteen years.
Key Areas of Research
At present, the main emphasis of research efforts is in the area of RFIC design and is in direct response to the demand from RFIC design houses both locally and internationally. However, it is only made possible by building on the expertise and infrastructure already in place due to earlier design work at component level. Typical examples of projects recently undertaken include a SiGe front-end for WLAN applications at 5 GHz. This RFIC design, which was carried out in association with the Cork division of Motorola SPS, serves as a technology benchmark for this new process. The IC incorporates a LNA and tunable filter.
Work on a novel bandpass sigma-delta ADC is being carried out in conjunction with the Cork division of M/A-COM. The aim is to design and realize an integrated bandpass sigma-delta analog-to-digital converter that will accept an input signal of 860 MHz and operate over a bandwidth of 20 MHz. Unusually, the IC is based on pHEMT technology and aims to leverage the advantages that these devices offer in certain situations.
The topology of the modulator is a fourth-order, continuous-time bandpass unit, which is followed by a FIR bandpass filter and two stages of digital decimation. Also designed into the IC are a 3.44 GHz clock generator using a pHEMT VCO, an integrated LC bandpass resonator and a 3.44 GHz RZ comparator.
Nothing has yet been published on either of these projects as work is ongoing and there is still some commercial sensitivity attached both to the processes and circuit designs.
M/A-COM, Motorola, Analog Devices and RF Integration have all located RFIC design centers in Cork, whilst Farran Technology, M/A-COM, SMT, Bourns and Com21 are engaged in component level RF design. In addition, companies such as Parthus, S3, Xilink and Cypress Semiconductor are doing silicon IC design that often fringes on RFIC design.
UCC has close ties with all of these companies and most postgraduate students are engaged in research that is directly funded by, and coordinated with, these sponsors.
Professor Patrick J. Murphy, Department of Electrical and Electronic Engineering, University College Cork, Ireland. Tel: + 353 21 490 2214; e-mail: email@example.com.
University College Dublin (UCD)
The RF and Microwave Research Group is headed by Professor T.J. Brazil, who is part of the Electronic and Electrical Engineering faculty.
Against a background of exceptional worldwide growth in digital communications and the rapid development of wireless-based systems the central focus of the RF and Microwave Research Group is the development of CAD models and software tools for nonlinear applications of high frequency engineering. Work includes the validation of these tools by checking their predictions against experimental measurements.
Key Areas of Research
Individual research projects are briefly described, outlining the scope, progress, future work, sponsors and collaborators. First, nonlinear equivalent circuit modeling and characterization of high frequency transistors has been a major research theme within the group, and has been extended to new device technologies and material systems, both III-V and silicon-based. The importance of this kind of modeling is growing in high frequency circuit design, which is increasingly oriented towards MMIC implementation. Stringent system specifications place severe demands on model predictive accuracy, while at the same time models must be Ôcompact' and efficient.
The COBRA model for pHEMTs and MESFETs developed at UCD has proven to be an excellent general-purpose scalable representation for these kinds of devices, and has undergone significant improvement and refinement to address non-quasistatic and dispersion issues. Extensive verification tests have been performed on manufacturer processes from GEC Research (UK) and PML (France), and the model has been successfully implemented in fully compiled form in Agilent design software.
In recognition of the difficulties experienced by users in extracting parameters from experimental characterization for all models of this kind, a comprehensive new software tool (COMET) for parameter extraction has been developed with a professional Windows interface. Work has also begun on extending the COBRA model to silicon RF-CMOS devices and to advanced SiGe HFETs, in collaboration with the University of Ulm and Daimler-Chrysler Research, Ulm, Germany.
Another stream of modeling activity has continued in the area of heterojunction bipolar devices, both AlGaAs/GaAs HBTs and silicon HBT devices using graded SiGe in the base region. This work has been sponsored by the Enterprise Ireland Strategic Research Program and the EU TMR Network Program, in collaboration with GEC Research UK, Philips Microwave Limeil, France, Queen's University, Belfast, Daimler-Chrysler Research, Parthus, and the University of Ulm, Germany.
Second, work sponsored by the Enterprise Ireland Strategic Research Program investigates the identification of Volterra series kernels for nonlinear microwave systems. The Volterra series representation allows an efficient general description of nonlinear systems, but the computation of the Volterra kernels present considerable difficulties in all but the simplest cases. In this project, a digital modeling methodology has been developed based on an extraction from random, time-domain, discrete input-output data, which allows the calculation of an effective, Volterra mapping-based equivalent model in discrete frequency for nonlinear RF/microwave circuits and systems.
From this, a variety of system performance parameters may be readily determined, such as harmonic or intermodulation distortion with high accuracy up to moderate levels of gain compression. An extensive program of experimental amplifier development and test has verified the usefulness of this approach in design.
Also sponsored by the Enterprise Ireland Strategic Research Program is an asymptotic waveform evaluation applied to microwave distributed circuits. Asymptotic waveform evaluation (AWE) has emerged mainly from research into interconnection effects in high speed digital electronics. Based on an expansion of the transfer function in the Laplace domain, the time-domain moment may be computed recursively and the transient response determined with high efficiency, as only the essential dynamics of the system are retained. Extension of this concept from large RC networks to generalized distributed networks, such as are found at microwave frequencies, has proven difficult.
A variety of techniques have been explored to address this problem, including complex frequency hopping and Padé-via-Lanczos methods. A new approach to the accurate computation of higher order moments in AWE has been demonstrated.
Another key project involves the application of neural networks to system-level behavioral modeling of power amplifiers (PA) for use in high frequency CAD. A novel frequency dependent neural network behavioral model of a PA has been developed, which succeeds in decreasing simulation time and increasing the accuracy of existing behavioral models.
The neural network is used to expand the parameter range of conventional behavioral models of a PA and maps the transfer characteristics of the various behavioral models (based on the amplitude modulation-amplitude modulation (AM-AM), amplitude modulation-phase modulation (AM-PM) functions) over a specified RF frequency range. The model is used to evaluate the spectral regrowth characteristics by calculating the Adjacent Channel Power Ratio (ACPR) for a wideband CDMA (W-CDMA) signal at different RF carrier frequencies. A new transform has also been developed which enables a neural network to describe an envelope behavioral model directly from AM-AM and AM-PM data.
In the field of high frequency power amplifier analysis, design and linearization research has been carried into various aspects of CAD-based analysis and design of PAs. Recently this has been extended to linearization studies for broadband power amplifiers handling multiple W-CDMA carriers.
The analysis and design aspects have emphasized two approaches, one based on classical behavioral models using AM-AM and AM-PM characteristics, and a second using exact time-domain transient analysis involving a combination of state-space and convolution techniques, developed previously at UCD. This has allowed a rigorous comparison of the two approaches to be undertaken, and has led to the development of a new computer-based 'load-pull' PA design tool, which can be used to achieve an optimum trade-off between RF performance and linearity using a realistic distributed circuit environment.
Recently, a new research program has been initiated into the linearization of wideband PAs with significant memory using an inverse complex baseband Volterra series technique.
Professor Thomas J. Brazil, Department of Electronic and Electrical Engineering, University College Dublin, Dublin 4, Ireland. Tel: +353-1-716 1909; e-mail: firstname.lastname@example.org.
Politecnico di Milano
The microwave research activities are developed and progressed by G. Macchiarella, M Politi and G.G. Gentili in the Dipartimento di Elettronica e Informazione (Department of Electronics and Information).
Significant research into microwave filters began many years ago with the development of CAD procedures for post-coupled waveguide filters and for comb and interdigital filters in slab line. At present, most of the work under development in this area is devoted to mobile communications applications.
Key Areas of Research
In order to investigate synthesis filters theory, novel methodologies are being studied for the synthesis of equiripple Chebycheff filters with arbitrary placed transmission zeros (either complex or imaginary). Original procedures have been developed which, starting from the required filter mask, enable the determination of the coupling coefficient of an arbitrary filter topology, built up as a cascade of triplet and/or quadruplet sections.
The design of dielectric dual-mode resonators for basestation applications is also being considered. A suitable coupling mechanism for this application has been found and a design procedure for dual-mode filters is under development. However, the aim of the work on modeling techniques for generalized comb filters is to derive suitable equivalent circuits for this class of multiple-coupled-cavity filters from electromagnetic simulations, for application in novel filter design methodologies such as space mapping.
In another study procedures are being considered for computer aided tuning of microwave filters. Original strategies are being investigated for partial or complete tuning automation of mobile basestation filter units (diplexers). Elsewhere, theoretical and experimental studies are being carried out into the generation of passive intermodulation in comb cavities with the goal of deriving a suitable modeling technique for this phenomenon.
Most of the above activities are supported by external organizations, especially for experimental work such as the fabrication of prototypes for verification. Financial support is obtained mainly by developing CAD procedures or feasibility studies. At present the polytechnic has research contracts with Forem (Allen Group), Ericsson Lab Italy, Cselt and Alcatel. Forem and Ericsson also support PhD and postdoctoral fellowships for studies into filter technologies.
Methodologies are being investigated for the efficient implementation of various numerical methods for electromagnetic field solutions. These include: a boundary integral for reciprocal and non-reciprocal media; representation of multimodal interacting structures with monomodal equivalent circuits; the solution of inhomogeneous resonators with mixed methods (mode-matching and finite elements); and the analysis of 2D/3D microwave structures by finite integration techniques, including the development of special techniques for equivalent parameters extraction.
This year some activities have begun in the area of active circuits. In particular there is research into the design of very low phase noise integrated oscillators in SiGe technology, which is supported by Ericsson Lab Italy. Similarly, the investigation of techniques for computer analysis and design of a feedforward linearizer for last generation mobile systems is supported by Forem.
Giuseppe Macchiarella, Department of Eletronics and Information, Politecnico di Milano, Piazza Leonardo Da Vinci n. 32, 20133 Milan, Italy. E-mail: Giuseppe.Macchiarella@ polimi.it.
University of Perugia
The Dipartimento di Ingegneria Elettronica e dell'Informazione (Department of Electronics and Information Engineering (DIEI)), chaired by Professor Patrizia Basili, has a staff of about 30 professors working in various areas of electronics and information technologies. Within the DIEI, a group of researchers led by Professor Sorrentino has formed the Microwave Electronics Laboratory (MEL).
Experimental facilities of the MEL include a clean room (classes 10000, 1000 and 100 under laminar air flow) equipped with photo-etching equipment and a wire bonder for the manufacturing of microwave hybrid planar circuits, and a test and measurement set-up (probe station for on-wafer microwave measurements up to 40 GHz). At present, the laboratory is used for manufacturing hybrid integrated circuits up to 20 GHz and for the testing of waveguide circuits up to 60 GHz.
For many years the MEL research group has been involved in the modeling and computer-aided design of microwave and millimeter-wave circuits using various technologies, from conventional (waveguide) to hybrid and monolithic integrated circuits and antennas. Computer codes, based on rigorous numerical methods such as mode-matching and finite difference time-domain methods, have been developed and constantly updated and enhanced. Attention has been devoted to the development of very efficient optimization algorithms, based on the adjoint network method. Recent advancements include the FDTD modeling and design of quasi-optical components and active antennas.
Key Areas of Research
In order to develop the global modeling of microwave electronic circuits recent efforts have been devoted to the development of an FDTD simulator. This has resulted in a powerful tool for the analysis of structures with arbitrary geometries. The code features a variable mesh to locally improve the resolution without affecting the computational effort and various types of absorbing boundary conditions (Mur's first and second orders, perfectly matched layer (PML), modal absorbing boundary conditions (MABC), etc.). Also, antenna and scattering problems can be dealt with using near field-to-far field transform and plane wave excitation, and lumped element (LE) models, both linear and nonlinear, can be inserted into the 3D grid in order to simulate the interaction with the EM field, obtaining the so called LE-FDTD.
The code has recently been extended to model the interaction between electromagnetic fields and electronic devices (diodes, BJT, etc.) obtaining the so-called Ôglobal' simulator. Within the framework of a full-custom IC design, technology-oriented modeling techniques are especially useful where no equivalent circuit, thus no device-parameter extraction procedure, is needed. Instead semiconductor transport equations can directly be solved over a distributed arbitrary domain. This strategy, usually referred to as global modeling, is based on the self-consistent solution of Maxwell's equations and charge transport equations. The derivation of the combined field and device simulation scheme consists of solving the curl Maxwell's equation in conjunction with the Boltzmann transport equations.
This approach is specifically apt to the modeling of radio frequency circuits where a strong interaction occurs between the electromagnetic field and the solid-state devices. This is typically the case of packaged MMICs, distributed solid-state devices, quasi-optical structures, active integrated antennas, etc.
Within a European Union-funded collaboration among various European universities and industries, a project has been undertaken aimed at modeling quasi-optical frequency multipliers. For a basic quasi-optical frequency doubler the frequency multiplication is achieved by a diode bridge connected to the centers of two l/2 dipoles. The dipoles are placed in a cross configuration (referred to as crossed dipole). The longest one receives the incoming power at the fundamental frequency (3.5 GHz in the prototype), whilst the shortest one transmits the generated power at the doubled frequency (7.0 GHz in the prototype).
A good input-to-output isolation is achieved since incoming and outgoing waves are orthogonally polarized. Moreover, good conversion efficiency is achieved thanks to the symmetry of the structure (only even harmonics are generated within the multiplier). The conversion efficiency of the multiplier is intrinsically limited by the omni directional nature of both receiving and transmitting dipoles.
To overcome this problem, the front-to-back ratio (thus the directivity) of both receiving and transmitting dipoles has been increased by additional parasitic elements. The resulting structure essentially consists of two orthogonally polarized Yagi-Uda antennas. The new multi-layer structure employs two parasitic elements (reflectors), one for each dipole of the frequency doubler. The LE-FDTD code has been used to probe the E-field distribution in the active plane and to Fourier-transform those values into the frequency-domain. Results have clearly shown the polarization separation between the two frequencies.
Another project has been undertaken aimed at the modeling and design of printed reflect array antennas for spatial application. Printed reflect array antennas combine some of the best features of the conventional parabolic reflector antennas and microstrip array technology. They consist of a flat array of microstrip patches or dipoles printed on a dielectric substrate. A feed antenna illuminates the array whose individual elements are designed to scatter the incident field with the proper phase required to form a planar phase surface in front of the aperture.
For a parabolic reflector, the reflect array can achieve very good efficiency (greater than 50 percent) for a very large aperture since no power divider is needed, ensuring a very small insertion loss. Electronic phase shifters can be implanted into the elements for the reconfiguration or the scanning of the antenna beam. From a commercial point of view, all the above characteristics make reflect arrays particularly suited for spatial applications and as smart antennas in terrestrial wireless links.
The main objective of the work carried out at the University of Perugia is the development of a compact electronic phase shifter suitable for printed reflect arrays. In particular slot-coupled patch antennas and varactor-based phase shifters are currently under investigation. The modeling of such antenna elements is another research topic of interest. To this purpose the global simulation strategy is adopted. One of the key findings is the implementation of a new algorithm that allows nonlinear lumped elements (such as Schottky or varactor diodes) to be treated in a very efficient and accurate way within the LE-FDTD computational framework.
Future work will be devoted to the design, realization and measurement of small reflect array antennas operating at 10 GHz, as well as to the development of the control board necessary to achieve the beam reconfigurability.
Professor Roberto Sorrentino, University of Perugia, Microwave Electronics Laboratory. E-mail: presing@ unipg.it.
Warsaw University of Technology
The Faculty of Electronics and Information Technology consists of six institutes, and microwave research is carried out at three of them, including the Institute of Microelectronics and Optoelectronics, under the directorship of Dr Andrzej Pfitzner, the Institute of Radioelectronics, headed by Professor Jozef Modelski, and the Institute of Electronic Systems, under the directorship of Professor Janusz Dobrowolski.
The work highlighted here has been carried out under the directorship of Professor Bogdan Galwas in the Microwave Electronics and Photonics Division at the Institute of Microelectronics and Optoelectronics.
Studies into the microwave characterization of dielectric materials began five years ago with the development of a resonant dielectrometer to measure moisture in sand. At present, most of the research activities under development in this area are devoted to wideband measurements of biological tissues and chemical liquids.
Key Areas of Research
Focus has been on the analysis of a coaxial line/circular waveguide junction. A suitable solution to the boundary value problem of a structure with a waveguide of arbitrary radius filled with a layered material has been studied. A full wave analysis of the junction via a mode-matching technique has been elaborated and the analysis of a junction with a dielectrically loaded waveguide is under development.
The aim of another study to consider modeling techniques for dielectric probes is to derive suitable models and calibration methods for broadband probes from electromagnetic analysis and measurements.
Professor Jerzy Piotrowski is leading a study into the application of a coaxial/circular waveguide below cut-off junction for measurement of dielectrics in microwaves. The objective is theoretical elaboration as well as the use of numerical and empirical tools of the broadband and resonant methods of dielectric measurements.
The junction of a coaxial line and a circular waveguide with a layered medium has been investigated by the mode-matching method in which the fields on each side of discontinuity at the junction plane are expanded in an infinite series of modes matched across the boundary to preserve continuity. The solution of the field equation yields the normalized admittance at the junction plane, which is related to the complex permittivity of the material under test.
The broadband and resonant probes with a built-in junction have been modeled in order to predict the relationship between the measured reflection coefficient at the probe input and the permittivity of any dielectric sample. Suitable equivalent circuits have been developed and their validity checked by frequency measurements of the probes. Applications include the measurement of biological tissue, liquids or moisture in granular materials. The research is being aided by the investigation of a junction with a dielectrically loaded waveguide, and models of probes with a non-uniform waveguide insert along the radius should be developed.
There are plans to develop a measurement system with a resonator sensor or a broadband probe dedicated to specific industrial applications.
Professor Bogdan Galwas, Warsaw University of Technology, Faculty of Electronics and Information Technology, Nowowiejska 15/19, 00-665 Warsaw, Poland. Tel: (+48 22) 825-37-58, (+48 22) 660-7497.
St. Petersburg State Technical University (SPbSTU)
SPbSTU is one of the leading Russian university research centers engaged in microwave research. Projects in this field are supported by the Physical Electronics Department headed by Professor A. Fotiadi, the Radio Engineering and Telecommunications Department lead by Professor I Tsikin and the Radiophysics Department under Professor V. Nikolaev.
The most characteristic feature of microwave research in the university is the very broad scope of the subjects studied, including active and passive elements, meter through sub-mm waveband, signal processing and ultra-high power devices.
Key Areas of Research
Some of the most recent and ongoing fields of research investigated in the various departments include Professor Usychenko's study of the fluctuations in various types of oscillators and amplifiers that investigated the fluctuation characteristics of solid-state and vacuum devices. Low frequency noise models for cm- and mm-wave solid-state devices have been developed, and the main attention has recently been directed towards the fluctuation processes in crossed-field tubes and the physical nature of excessive noise in magnetron devices.
Microwave ferrites are being studied by Dr. Zagriadski and his team, covering wave-guiding structures and devices, multi-layer microwave integrated circuits and radiating structures based on thin ferrite films and complex ferrite composites, and passive and active elements (filters, delay lines, power limiters, signal-to-noise enhancers, resonators, oscillators, active filters, etc.) with magneto-static wave (spin-wave). Recent efforts have focused on the problem of the electrodynamic description of non-reciprocal bianisotropic media including stripline-coupled magneto-static wave resonators in dielectric matrix. This was solved via calculation of polarizability sensors for an arbitrary direction of the bias magnetic field and an arbitrary resonator shape.
The team headed by Dr. Zaitsev has been investigating millimeter-wave phased-array radiators. Low cost mm-wave electronically scanned antennae have been developed for diverse applications. Such antennae are based on a planar integrated ferrite traveling-wave structure, controlled by the magnetizing of ferrite elements, so that for 1D scanning only one control current is required, while for 2D beam control two control currents are needed.
Mathematical models of such antennae and software for their digital simulation have been created. Samples for 11 to 12 GHz, 35 to 37 GHz and 75 GHz frequency bands passed experimental testing and demonstrated expectedly good parameters. An active version of the antenna with higher performance is now being considered.
High power microwave vacuum devices with intense electron flows have been the focus of studies by G. Sominski and his team. New low disturbing diagnostic methods with good resolution in space (up to ~10Ð2 Ð10Ð1 mm), time (up to ~10Ð10 s) and electron energy (up to about 1 percent or better) were proposed and used for investigating non-uniform and non-stationary dense electron flows of high power microwave tubes. Space charge oscillations, varying in nature, were discovered in electron flows confined in magnetic or crossed fields, and were found to have a strong effect on the confinement quality and the electrons' energy spread.
A connection between the parasitic components in output spectra of oscillators and amplifiers with the space charge oscillations has been demonstrated. Static and RF field non-uniformity, spurious emission processes, and secondary flows of particles and plasmas are among the factors determining excitation and parameters of space charge oscillations, thus indirectly influencing electron flow confinement and the performance of devices. These findings open up promising possibilities for electron flow quality control and the improvement of conventional tubes with the potential for developing new types of microwave devices.
As an illustration of the last example, on the basis of a decimeter-wave amplitron with a secondary-emission cathode, a high power source of quasi-chaotic radiation has been developed. In this device, intense oscillations of electron space charge along the magnetic field direction are pumped up with a special RF signal introduced near the end shields of the cathode. Chaotization of the oscillatory process in the system yields wideband (more than an octave) 100 to 120 kW signal at the output. Total efficiency, taking into account the pumping signal power, may be as high as ~40 percent. This new device could find numerous applications in various areas, such as nonlinear radars, communication, non-equilibrium plasma chemistry, etc.
Plans of the high power electronics research team include the search for effective methods of control over operation of high power microwave devices through non-uniform static or RF field effect. The work will be aimed at solving practical problems by investigating methods for the suppression of parasitic low frequency radiation in gyrotrons and the design of effective depressed-collector systems for TWTs.
Professor Gennadi Sominski, Physical Electronics Department, St. Petersburg State Technical University, 29 Politechnicheskaya Street, St. Petersburg 195251, Russia. Tel: +7(812) 5526127.
Swiss Federal Institute of Technology, Zurich
The Laboratory for Electromagnetic Fields and Microwave Electronics is part of the Information Technology and Electrical Engineering Department, and comprises two research groups with complimentary research interests. Professor Vahldieck heads the Electromagnetic Fields Group, whilst Professor Bächtold heads the Microwave Electronics Group.
The Electromagnetic Fields Group pursues research in computational electromagnetics in the area of CAD of passive microwave/millimeter-wave components, electromagnetic compatibility, integrated optics and nano-optics. Current projects are on automatic tuning and optimization techniques for microwave and millimeter-wave filters using a novel combination of rigorous field solvers/measurements with generic circuit prototypes, numerical analysis and optimization of reverberation chambers, FEM modeling of optical MQW rib waveguide structures in traveling wave photodiodes and their integration with passive uniplanar microwave and millimeter-wave circuits, photonic bandgap structures for guiding and filtering electromagnetic waves at millimeter and nanometer wavelengths, and numerical analysis of plasmon resonances using a finite element solution of the EFIE.
The research of the Microwave Electronics Group focuses on MMIC design and characterization, measurement techniques, millimeter-wave device and circuit technology, optoelectronics and integrated optics. Over the last 10 years the emphasis has been on device modeling and circuit design for wireless communication applications using GaAs MESFETs foundry technology. Shared projects between both groups focus on photonic bandgap structures and on highly integrated front-end design for 5GHz channel sounders in MMIC and LTCC technology.
Key Areas of Research
The key projects being undertaken by the Electromagnetic Fields Group include work on the automatic tuning of filters and diplexers. The aim is to develop an automatic filter tuning method suitable for application on the production floor. The initial approach was to measure a roughly tuned microwave or millimeter-wave filter and approximate the measured data by a prototype network characterized by a polynomial function. The coefficients are found from optimization by setting the measured data as target values. The element sensitivities are found in a similar way, thus allowing the optimization of a filter almost exclusively by optimizing the coefficients of the polynomial. By using a general field solver instead of measurements other complex microwave structures can be optimized in the same way. The advantage here is that the field solver needs to run only a few times to correct the network model.
A project on MQW rib waveguide structures and integration with uniplanar microwave circuits sets out to characterize transitions between photonic waveguide structures and coplanar transmission lines for highly integrated microwave/optical front-ends. Here the team is investigating the direct integration of a traveling wave photodiode with an active uniplanar antenna.
Furthermore, a study of plasmon resonances works from the basis that certain colloidal particles like silver or gold can exhibit a resonant behavior at optical wavelengths. The extremely large electromagnetic fields associated with these plasmon resonances are of great importance for surface enhanced Raman scattering and in applications where nanoparticles are used as biological markers. Under investigation is the realistic situation of nonregular-shaped nanoparticles and what has been found is an extremely complex spectrum of resonances. Also under study is the possibility of utilizing plasmon resonances in light guiding structures and filters.
A photonic bandgap (PBG) structures study recognizes that the interaction of two- and three-dimensional periodic structures is of growing importance in such diverse fields as antenna technology, microwave integrated circuits and photonics and nano-structures. Here there is collaboration with the Microwave Electronics Group to investigate new PBG structures to guide and filter electromagnetic waves with the emphasis on numerical modeling. This and the effect of defects can be used to optimize the behavior of PBG structures. In this project rigorous numerical methods to model electromagnetic fields are further developed and optimization techniques based on genetic algorithms are also applied.
Current work of the Microwave Electronics Group has seen the development of a fully integrated RF front-end for a smart antenna Hiperlan receiver with three antennas providing the electronics for superposition of the three RF signals with controllable amplitude and phase. Presently MMIC developments are under way with commercial GaAs-MESFET, GaAs-pHEMT, silicon CMOS and silicon-germanium bipolar processes with projects on RF-transmitter/receivers in the 2.4, 5, 10 and 60 GHz ranges. Different linearization schemes for power amplifiers are under consideration.
In mm-wave device and circuit technology an indium-phosphide-based HEMT process has been developed. Using commercially available epitaxial InGaAs/InAlAs layers the HEMT devices with 0.2 mm e-beam defined gates show typical transit frequencies of 150 GHz. Recently the gate formation processes have been further developed for 0.1 mm gate length. Suitable models for active and passive coplanar on-chip devices have been developed and MMICs have been designed and manufactured for wireless short distance communication in the frequency range up to 60 GHz.
In an ongoing project extremely low noise cryogenic HEMT amplifiers are under development for applications in radio astronomy. A noise temperature of 5K has been measured in a two-stage amplifier operated at an ambient temperature of 15K. This is the lowest amplifier noise temperature achievable with any technology.
Ongoing projects are modeling and characterization of mode-locked laser diodes, 980nm pump lasers, VCSELs (vertical cavity surface emitting laser) and dense integrated optical components for WDM applications. Of particular interest are optical interconnects in electronic systems between boards and modules. Novel concepts of optical waveguide structures with new functionalities are now under investigation. In this sense, densification in the time scale and in the length scale is the leading paradigm for future THz photonics devices.
Professor Vahldieck, Swiss Federal Institute of Technology, Zurich, Switzerland. E-mail: vahldieck@ifh. ee.ethz.ch.
Research in the microwave field is carried out by the Wireless Communications Group of the Department of Electronic and Electrical Engineering, under Professor Vardaxoglou, who also heads the Center for Mobile Communications (CMCR).
The Wireless Communications Group is involved in theoretical and practical studies of antenna and wireless systems. The antenna research is primarily concerned with applications in microwave, mm-wave, satellite and mobile communication systems. In 1998 the Center for Mobile Communications Research was founded to research and develop antennas for mobile telephony and mobility. With broad expertise in a range of commercial and proprietary electromagnetic simulators, the center is structured to provide advanced solutions to its industrial partners.
Key Areas of Research
The following projects are currently running in the Wireless Communications Group: mobile telephone antennas; antennas for 3G communications; frequency selective surfaces (FSS); optically activated circuits and antennas; electromagnetic and photonic band gap structures; arrays and FSS for mm-wave; multichip interconnects; and RF systems. The work has been funded by the UK Engineering and Physical Sciences Research Council (EPSRC), and companies such as Sarantel, GEC, British Aerospace, Orange and local SMEs. The group also has major collaborative programs with Queen's University of Belfast and Politechnico di Torino, Italy.
The CMCR was established with the aim to design and develop prototype miniaturized antennas for wireless telephony. It is now well accepted that current and future mobile phone antennas need to perform a wide range of tasks to meet worldwide demands and should be easy to mass-produce. Owing to health considerations, the specific absorption rate (SAR) requirements are now widespread and mobile phone handsets will have to produce lower exposure levels. The center is currently looking into broadband, multiband and low SAR mobile telephone antennas for GSM, GPS, Bluetooth and UMTS applications. It has microwave measuring capabilities and rapid prototyping processes using the latest etching and laser technologies. Through pioneering this research, the design and development of a new antenna has been patented worldwide.
It is based on a helical design with a ceramic core within which the near field is enclosed. It can be installed very close to electronic circuits, mechanical objects and human tissue whilst still performing effectively. The dielectric loaded twisted loop antenna is designed to minimize the fields that are incident on the user's head. In addition, three of its variants for GPS, Bluetooth and dual band GSM/ UMTS are being researched.
In common with small antennas in general, the simple form of a twisted loop antenna has narrow bandwidth. The group is currently investigating several methods to achieve high efficiency and broadband response of the twisted loop antenna, such as mode coupling. The antenna has been shown to exhibit two modes, the single-ended mode and the balanced mode. Due to the high Q nature of the twisted loop structure, these individual modes have narrow bandwidths. However, broadband composite frequency responses can be achieved in a manner analogous to coupled resonator filter design by coupling resonant modes together.
This antenna technology reduces the need for filters (thus lower component costs) and for a large ground plane (low handset interaction). They can be embedded into the handset while the electrical noise is isolated by the balun, which increases the reliability and signal strength of short-range devices, such as Bluetooth.
Professor Vardaxoglou, Wireless Communications Group, Department of Electronic and Electrical Engineering, Loughborough University, Loughborough, Leicestershire, LE11 3TU, United Kingdom. E-mail: J.C. Vardaxoglou@lboro.ac.uk.
University of Surrey
The Microwave and Systems Research Group is headed by Professor Ian Robertson and covers RF, microwave, wave-wave, and THz circuit and subsystems engineering. The group is part of a project funded by the Joint Infrastructure Fund to create an Advanced Technology Institute (ATE).
The Advanced Technology Institute encompasses six research groups from three schools to stimulate cross-disciplinary research. They are microwave subsystems, lasers and optoelectronics, large area electronics, ion beam applications, high pressure and biosensor. The facilities include two RF-on-wafer measurement systems (45 MHz to 60 GHz and 45 MHz to 110 GHz), a full CAD suite (from HP-EEsof) and a laboratory-sized screened anechoic chamber.
Surrey is a major UK center for the design and application of MMICs. The activities are targeted especially on wave-wave circuits and subsystems for communications, radar, sensors and security systems. The group heads two major EPSRC collaborative projects. One involves the design of 60 GHz circuits for broadband mobile communications systems and 77 GHz circuits for radar applications, including automotive systems. The second is to develop a unique multi-chip module technology based on miniature multilayer rectangular waveguides for operation above 100 GHz.
Key Areas of Research
The two major EPSRC collaborative projects are highlighted below. Other areas of work include the study of low phase noise oscillators where a patented anti jitter circuit (AJC), which could prove as revolutionary as the phase locked loop (PLL), is being investigated. With its ability to remove wideband phase noise and timing jitter from any frequency source, it can restore reliability and low BER in computer and communications systems as clock speeds spiral even higher. There is also associated research on low noise current sources.
Research on small RF antennas for portable radio systems has shown that electromagnetic models and simulators give pessimistic performance pre-dictions. New EM theory, new measurements and new simulations are being investigated which challenge conventional understanding.
In the field of amplifier linearization, techniques have been considered for reducing intermodulation in amplifiers by using a harmonic injection technique. In one method the second harmonic of the input signal is generated and then fed into the input of the microwave amplifier. Significant reductions in third-order intermodulation products have been achieved.
The Microwave and Systems Research Group has been at the head of two major EPSRC collaborative projects. The first is a collaboration with the University of Glasgow, investigating advanced techniques for the realization of MMIC-based wave-wave signal processing for data communications at 60 GHz and radar applications at 77 GHz. These techniques are based on the use of mm-wave modulators and demodulators under DSP control. This approach can lead to lower RF complexity and hence lower costs and lower DC power consumption. Using these techniques, a wireless data communication link at V-band and a handheld radar at W-band are being developed.
Achievements have included the successful design and test of MMIC single-chip transmitters and receivers operating at 18, 28, 38 and 60 GHz, with applications including indoor radio networks, broadband mobile systems and LMDS.
The second EPSRC project collaborates with the Universities of Kent and Glasgow, considering 75 to 300 GHz multi-chip modules (MCM). The project investigates an advanced new concept for wave-wave MCMs based on dielectric-filled metal pipe rectangular waveguides. This transmission medium will provide low loss interconnects into which MMICs can be inserted directly with no bond-wire interface except for DC and IF connections. The technology can be used to build up complex subsystems for use in communications, radar and sensor applications. Demonstrators using InP MMICs are being developed operating at 77 and 140 GHz.
Professor Ian Robertson, Microwave and Systems Research Group. Tel: +44 (0) 1483 259862; e-mail: email@example.com.
Commercial and Pan-European Research
In addition to academic establishments, commercial and independent research centers are playing a crucial role in the development of new technology. Commercial confidentiality and competitive sensitivity often limit what companies are willing to divulge. Therefore, Microwave Journal is grateful to those who have contributed. The three Pan-European projects highlighted are examples of commercial and academic cooperation on subjects specific to Europe but with potentially global implications.
Ericsson Microwave Systems AB
The Microwave and High Speed Electronics Research Center is managed by Dr. Thomas Lewin.
The research center was founded in 1991, with its efforts focused on high speed electronics, and by 1995 it had become one of the worldwide leaders in this research field. Today it has about 15 employees working mainly in microwave-related areas. These include microwave and mm-wave integrated circuits, passive microwave components, such as RF filters, advanced packaging technologies and photonic telecommunication systems.
Key Areas of Research
In the passive microwave components field the research center is currently participating in a European Union program to develop RF bandpass filters aimed at the 5 to 10 GHz frequency range. They are based on bulk acoustic wave devices using piezoelectric thin films and are intended for mobile communication systems. The program has been running for two years and filters should be available by the end of 2002.
The research center is also involved in another EU project that started recently and aims at microwave electronics with tunable dielectric layers. Two system level applications are considered to demonstrate the advantages of the new technology. One is a ferroelectric plate (lens) performing a beam-scanning function, equivalent to a complex phased array antenna. The second is a re-configurable/adaptable phased array antenna in the form of a multi-component assembly, where all components are electrically controlled and based on ferroelectric materials manufactured in single or similar technologies. These cost-effective antennas are proposed for radio links and similar applications in advanced microwave communications systems.
For many years evaluation of SiGe technology has been one of the center's major activities. In 1997, it became engaged in the BETA EU project to evaluate various SiGe heterojunction bipolar technologies via construction of microwave monolithic integrated circuits (MMIC) and state-of-the-art results have been achieved. In parallel to this, a bilateral program between Ericsson Microwave and Hitachi has pushed the application of SiGe technology upward in frequency well into the mm-wave range. Some of the achievements are described in more detail below.
The activities related to SiGe technology are devoted mainly to microwave-radio applications where cost reduction is one of the key issues.
SiGe technology provides a cost-effective solution with performance sufficient for many microwave applications. The objective of this specific SiGe project is to explore to what extent SiGe may be used to replace today's more costly technology in microwave and mm-wave radios. The technology is evaluated by constructing MMICs with varying degrees of integration, with analysis focusing on both performance and cost.
Circuits and subsystems that have been constructed include low noise amplifiers at 5, 23 and 38 GHz, voltage-controlled oscillators at 5, 8 and 23 GHz, mixers at 8, 23 and 38 GHz, a fully integrated frequency synthesizer (8/16 GHz) and an image-reject receiver (8 GHz). In addition a wave-wave amplifier (TWA) was also designed for broadband application.
Some state-of-the-art results were obtained from the program. Typical phase noise results are 100 dBc/Hz at 100 kHz offset for the 5 GHz VCO and 97 dBc/Hz for the 8 GHz VCO. For the LNA a gain of 20 dB and noise figure of 4 dB were measured at 23 GHz, which is the highest operation frequency for SiGe LNAs reported so far. The TWAs demonstrated 8 dB gain and a 3 dB bandwidth of about 65 GHz. This is the highest bandwidth on Si-based technology for this type of amplifier and has the potential for application in optical communication systems.
The achievements outlined above indicate that SiGe technology will be applicable for most microwave applications for frequencies well above 30 GHz. With recent advances in SiGe technology, 180 GHz fmax (Hitachi) and 210 GHz fT (IBM), the implications are that SiGe technology has the potential for analog ICs up to 60 GHz and for high speed ICs up to 100 GHz. Therefore, SiGe is opening up a new market for low cost, high volume and high frequency products which Ericsson Microwave will continue to develop.
Thomas Lewin, Ericsson Microwave Systems AB, Microwave and High Speed Electronics Research Center, 431 84 Mšlndal, Sweden. E-mail: firstname.lastname@example.org.
Malvern Technology Park, St. Andrew's Road, Malvern, UK.
Microwave Circuits and Prototyping.
The group is engaged in the design of custom microwave and mm-wave circuits and prototype modules, including MMICs for frequencies up to 100 GHz. The group has access to a wide range of MMIC fabrication processes worldwide, and benefits from close working relationships with commercial foundries within both Europe and the US. Having developed a design, measurement and packaging capability based on over ten years experience in this field, the group works at the forefront of advanced microwave circuit design, servicing a wide range of military and commercial customers. The majority of work is targeted at the design and development of advanced prototypes for mm-wave platforms.
Key Areas of Research
QinetiQ Malvern has built up a wide range of expertise in the field of microwave circuit and subsystem design. The main focus for current work is the design, development and demonstration of highly integrated mm-wave multi-function circuits. These are aimed at a number of application areas, including short-range communications, satellite-based communications and phased arrays. The group is also engaged in the design and prototyping of novel packaging techniques.
A number of state-of-the-art microwave and mm-wave transmit and receive subsystems have been developed, including fully integrated MMIC receiver and transmitter front-ends for 40 to 50 GHz, a single-chip image reject receiver for 60 GHz, targeting WLAN and covert communications applications, and a 12 to 18 GHz single chip transceiver.
Research has recently begun into the circuit requirements of both military and civil communications systems operating in the 35 to 45 GHz frequency range. Civil applications include point-to-point and point-to-multipoint communications. The results have yielded a program of work involving the design, fabrication and evaluation of multifunction MMICs for both transmit and receive functions. These circuits include fully integrated transmit and receive single-chip front-ends, manufactured using commercially available GaAs pHEMT technology. Both of these integrated designs have demonstrated state-of-the-art performance, and have been integrated into system demonstrators.
The integrated receiver MMIC covers an RF range of 40 to 45 GHz. This chip measures 3.9 mm by 3.2 mm, and has a single sideband conversion gain in excess of 11 dB, operating from an input reference LO of 19 GHz. The LO is doubled in frequency on-chip, enabling the receiver to operate over an IF range of 2 to 7 GHz. The lower RF limit can be extended below 40 GHz, by operating the chip in lower, rather than upper sideband mode.
The integrated single-sideband transmitter MMIC operates over a frequency range of 42 to 50 GHz, from an LO of 19 GHz. The chip, measuring 4.4 mm by 3.2 mm, gives a single-sideband output with a conversion gain in excess of 6 dB.
QinetiQ aims to develop this work further by attracting industrial partners engaged in the development of advanced mm-wave communications systems, such as LMDS and MVDS.
The research team intends to continue focusing on the development of advanced microwave and mm-wave circuits and subsystems targeting the needs of communications and sensing platforms for the 21st century. They now use their technical background and expertise to offer custom design, contract research and technical consultancy on a commercial basis.
David Bannister, Room PA125, QinetiQ, Malvern Technology Park, Malvern, Worcestershire WR14 3PS, United Kingdom. E-mail: dcbannister @QinetiQ.com.
MEDCOM - Microwave Electro-acoustic Devices for Mobile and Land-based Communications.
The broad objective is to develop and test new technologies based on new thin piezoelectric films for the fabrication of the next generation of microwave electro-acoustic devices used in mobile and land-based communications. Specific objectives include the synthesis of the piezoelectric films with high Q-factor, high coupling coefficient, low propagation losses and low TCF. The latter is also dependent on the substrate, so a number of substrate materials will be explored. Suggested materials are AlN and PZT on high velocity substrates such as polycrystalline diamond, as well as Si, glass and others.
Another objective is to demonstrate the industrial viability of the new fabrication processes, which will be further developed for large area substrates. Further, prototype bandpass filters operating between 2 and 7 GHz will be designed and manufactured. Finally, a communications subsystem will be constructed using the prototype filters to test them in real systems as well as to demonstrate the viability of the new technologies.
The work began in February 2001 and is scheduled to conclude at the end of January 2003. The project can be roughly divided into four main phases-materials development work, fabrication technology, prototype design and fabrication, and demonstrator construction, respectively. In the materials development phase a range of piezoelectric materials in combination with a number of substrate materials will be explored. This includes the synthesis of thin piezoelectric films of AlN, PZT and related materials on Si, glass, polycrystalline diamond, etc. The growth processes will be optimized in view of obtaining layered structures with the desired electro-acoustic properties. To this end a number of PVD deposition processes will be explored namely DC, pulsed DC and RF reactive sputter deposition. The compositional and structural properties of the films will be studied with ESCA, RBS, SIMS, XRD, hi-res XTEM, AFM, SEM, etc., and will be related to the desired electro-acoustic properties.
The second phase includes the development of all fabrication processes on large area substrates-deposition, lithography, etching, metallization and micro machining. Scaling up the deposition processes requires the development of a new PVD reactor in view of growing films on large area wafers with uniformity better than 1 percent. The third phase includes the design and fabrication of prototype SAW and BAW filters according to given specifications. The fabricated devices will be rigorously characterized and tested.
In the fourth phase a communications subsystem will be designed and constructed using the filters fabricated in phase three to demonstrate and test the new devices in real systems. It represents a frequency upconverter consisting of a voltage-controlled oscillator, a mixer, and low RF (2 to 3 GHz) and high RF (7 to 10 GHz) bandpass filters. RF measurements and characterization as well as testing of the subsystem will be carried out.
The prime contractor is Ilia Katardjiev from Uppsala University, Sweden. E-mail: Ilia@Angstrom.uu.se.
MultiKaRa - Multibeam Ka-band Receiving Antenna for Future Multimedia-via-satellite, Direct-to-home systems.
The worldwide demand for telecom services enabling high interactive data communication rates is growing. To remain competitive, the European Space industry needs to respond to this demand and build its own multimedia-via-satellite systems, providing direct-to-home interactive services for European citizens. The success of such systems requires on-board receiving antennae that can provide multi-beam coverage of the most populated regions. The best, most cost-effective solution suggests multi-beam satellite antennae in the Ka-band (18 to 31 GHz), the only non-saturated one available.
Development of such receiving antennae constitutes one of the most technical challenges for successful exploitation of multimedia-via-satellite systems, for which no satisfactory answer is available today. The MultiKaRa project will design and test innovative multi-beam receiving antennae around 30 GHz with its associated microwave circuits and evaluate its feasibility for future in-flight use.
Classical receivers with passive multi-beam antennae use a very light reflector with several horns located near the parabola focus, each connected to a separate satellite transponder. Required gain and isolation between spot-beams would need at least four receiving antennae and cumbersome motors to compensate for the spacecraft movements.
To overcome this problem, two new multi-beam antenna architectures will be evaluated, all permitting the use of a single antenna. The first is an active focal array fed reflector (FAFR) antenna with a single reflector, each horn contributing to several beams. It is electronically steerable for fine pointing. The main advantage is that the high gain is provided by the large reflector, with a minimum number of horns. Currently, such antennae have been implemented only in X- or Ku-bands, with a very limited number of beams (3 to 8, instead of 64 at present). The second is a FAFR with multiport amplifiers.
These two antenna architectures require a detailed trade-off phase before choices can be made and associated specifications ascertained. However, both use some common basic blocks, which constitute the main critical points for their feasibility, and these will be studied in MultiKaRa. These include: very low noise amplifiers, at about 30 GHz; signal matrix combiners with low loss, good amplitude and phase accuracy, together with small volume and mass; controllable MMIC phase shifters and attenuators; and cold thermal control, for lowering their LNA's noise figure.
The project began in January 2000 and is expected to be completed at the end of December 2001. Major milestones include: completion of the analysis of the different candidate antenna architectures with software simulation; detailed design and results from validation breadboards for the common critical blocks; completion of the demonstrator assembly; analysis of measurements on the critical parts and the overall demonstrator; and optimization proposals and overall conclusions on the architecture feasibility and suitability for in-flight purposes.
The prime contractor is Gerard Caille of Alcatel Space Industries: Tel: +33 5 34355526; e-mail: Gerard.Caille @space.alcatel.fr.
SMACKS - Surface Mount Assembly of Components for Ka-band Systems.
The aim of the project is to extend up to the Ka-band the SMT insertion techniques, which have already proven to be cost-effective up to the X-band. In order to achieve this, SMT organic and LTCC packages with high resonant frequencies (> 40 GHz) will be developed. GaAs will be enhanced by protection with BCB layer and a specific power MMIC will be developed. High performance filters on printed board will be studied and laminate substrates applicable up to the Ka-band will be investigated for SMT assembly. All these technologies will be assessed by the assembly and the validation of a complete transceiver module.
The six partners collaborating on this EC supported project are Thales, Alcatel, Labtech, Sorep, UMS and TNO.
Not applicable. Research Project TESMI - Teflon-based Stripline Circuits for Microwave Systems.
The main objective is to make available in Europe the manufacturing of pure Teflon-based stripline for microwave signal distribution/combination within subsystems, in order to optimize cost performance in all future information and communication systems involving microwave multicomponent assemblies. Classical combination techniques are either microstrip structures, which present shielding weakness, or mechanical stripline, which is more expensive and heavy. The TESMI project will allow manufacturers to avoid these drawbacks by achieving the adaptation of stripline to pure Teflon and provide first tests and validation trials.
The project began in September 2000 and is due to end on February 28, 2002. The work is shared in four work packages. The first is project management, whilst the second aims at adapting the common stripline manufacturing technology to the thermal and mechanical properties of Teflon substrate (dimensional stability, direct fusion bonding or thermoplastic adhesive interlayer, plated through via holes). Effectively this package presents dilatations in all the directions of space; as during the process, the Teflon can flow out of the structure due to pressure and high temperature. A design rule will be established in order to adapt the technology in such a way that is compatible with electrical requirements.
The next work package is dedicated to the validation of the manufacturing technology. Several test structures integrating standard technological limits will be manufactured. These structures will be relatively simple (propagation lines, coupled lines) and the measurement results will be compared to the simulations. Numerous electrical tests will be performed to determine high and low power applications, and behavior with temperature. Finally, new test structures will be designed and this second run will summarize the problems encountered in the first. The design will integrate more complicated passive structures to completely validate the technology.
A first run of stripline structures (three samples with a physical dimension of 10 cm by 10 cm and a respective thickness of 1.121 mm, 1.681 mm and 3.255 mm) bonded with a standard thermoplastic adhesive interlayer has been manufactured. This enabled the determination of the most important technological parameters, namely the temperature and the pressure during the process in order to avoid mechanical distortion and flow of the Teflon. Very little movement was observed during the etching process. Mechanical measurements show that the thickness of the stripline structure has the expected value and is constant on different positions of the structure. Measurements on twist show good results as well.
At present, the team is manufacturing other samples in different outlines (another sort of thermoplastic adhesive interlayer, direct fusion bonding, with plugs bonded within the assembly, and with areas relieved for plug insertion).
Project coordinator is Franck Durieux of Thales: Tel: 33 (0) 2 32 86 44 70; e-mail: franck.durieux @fr.thalesgoup.com. Project partner is Nick Potts of Printech Circuit Laboratories: Tel: +44 (0) 1245 323244; e-mail: email@example.com.
Research is the lifeblood of the microwave industry, capable of creating the excitement and momentum to push it forward. European academic and commercial research establishments are playing a key role in shaping the global future. Continued market buoyancy in the face of present uncertainties means sustained and focused research is fundamental. Projects must have commercial value with commitment to practical development in order for the microwave industry to evolve.
The author would like to thank all those individuals, institutes and companies who supplied research material for this supplement. It is impossible to list all of them here. However, you will find their names as key contacts at the end of each entry.
Tell us About Your Research Work
Following this inaugural overview of European microwave research activities, it is intended that Microwave Journal will regularly review developments. Therefore, if you are currently working on a relevant project in Europe please contact Research@mwjournal.com, outlining your work and giving contact details.