On the Right Wavelength: Microwave and RF Technology for Defence

Microwave (MW) and radio frequency (RF) applications such as advanced radars, missiles, communication, electronic warfare and Electronic Support Measures (ESM) act as battlefield force multipliers and are thus the focus of research and technology (R&T) activities of many ministries of defence throughout the world. With the demand for new MW and RF applications in military operations increasing, stakeholders should be aware of the changing defence environment and the necessity for addressing new capabilities. This article gives an overview of the challenges of defence R&T activities for MW and RF applications, presents the main drivers and current technology trends and, finally, touches upon how Europe addresses them by means of international cooperation under the aegis of the European Defence Agency (EDA). Illustrative EDA projects and programmes set good examples of how the international defence R&T collaboration contributes to the improvement of joint European defence capabilities.

The Changing defence environment
The nature of military threats is changing, from encounters in large scale open terrain to disparate, small scale pin-prick tactics in less explored and/or rough desert, urban or mountainous operational environments. Such threats call for new capabilities in the principal military domains—command, inform, engage, protect, manoeuvre and deploy—operating within an international network centric environment. In order to realise fully networked military operations, 'owning the spectrum' has become one of the prerequisites of successful information warfare, a trend that came along with the digitisation of the battlefield and the optimisation of the functional chain from the sensor to the shooter.

The technological response to these threats requires new MW and RF solutions, in general terms, to become smaller, more mobile, remotely engageable, consume less energy, be more accurate, highly integrated, versatile and robust. These broad common requirements drive R&T investments in MW and RF technologies on both the component and systemlevels.

While new capability needs will continue to emerge due to the changing nature of military operations, it is expected that as a result of the global economic downturn, most national defence budgets will be severely reduced in 2010 and beyond. Severe restrictions in public spending have meant that defence budgets in several countries have been reduced, from a few percent in some to more than 10 percent in others. As a result of budgetary restrictions, industrial defence capacities are shrinking, and the emphasis is moving from innovation to lobbying.

To meet these challenges, R&T efforts and budgets need to be more focussed, invested more efficiently and be more transparent, while military assets have to become cheaper, both in terms of operational and life cycle costs. International co-operation can be an effective tool for eliminating the adverse effects of budgetary restrictions and countering budget shortages.

Technological advances and economic liberalisation over recent years have dramatically increased the electromagnetic spectrum consumption in both the military and civilian domain. While military operations have become more complex and sophisticated in their use and need of spectrum, civilian stakeholders are placing great pressure on regulators to transfer more spectrum from governmental to commercial use. This requires the protection of current frequency bands and the allocation of new frequency bands for new MW and RF applications, alongside the need to explore new technology solutions able to tackle the scarcity of electromagnetic spectrum. Figure 1 shows the current allocation of frequency bands.

Drivers of new defence MW and RF technologies
Lessons learned from military operations in the last two decades show that forces and assets are usually dislocated in the homeland and intermediate logistical bases, as well as being scattered in the operational area. Typically, multinational units act in complex operational environments, which are diverse and unpredictable in most cases.

Operational environments for RF sensors are getting more and more difficult, offering up challenges that include dense electromagnetic spectrum (increased level of unintentional RF interference and increased pressure for commercial use of the spectrum), efficient Electronic Counter Measures (ECM), inhomogeneous natural environments, urban terrain, operations in brown water and poor weather conditions.

Targets to be detected, identified and tracked by RF sensors have become more difficult than ever:

• Small boats and sea skimming missiles in littoral scenarios
• Vehicles and personnel in the urban environment, people inside buildings and/or ground targets employing camouflage, concealment and deception techniques including concealment under foliage
• Mobile and fleeting targets
• Mines, Improvised Explosive Devices (IED) and mortars
• Low radar cross section and/or low altitude and/or low speed air targets (missiles, cruise missiles, UAS, etc.)
• High velocity and/or high altitude targets (satellites, ballistic missiles, supersonic missiles, reconnaissance aircraft, etc.)

The need for RF sensors with improved detection, identification and tracking capabilities is increasing, especially on board small unmanned platforms and long endurance air vehicles, as well as unattended ground and man-portable sensors. Large sensor networks, integrating thousands of nodes geographically distributed in large areas, also require significant improvements of RF sensors.

In addition, 'friendly fire' incidents highlight the need for a technological breakthrough in reliable non-cooperative target recognition, especially in adverse weather conditions when the recognition potential of RF sensors is strongly affected by meteorological phenomena. Also significant is the fact that modern military communication networks are expected to have the capability to be structured as smart subnets, regardless of which part of the electromagnetic spectrum their subsystems and devices operate. In addition, these networks must usually work in co-existence (or even interoperate) with civilian or commercial networks without interfering with them. At the same time they are exposed to local electrical and electronic systems, which may not comply with EMC regulations, thus creating electronic hazards.

In the homeland and intermediate bases, sustainable communication networks are required, with hubs and backbones being able to handle high traffic loads. Since stationary links and assets are highly vulnerable to attack, defence communication networks will continue to mainly rely on military satellite communications (Satcom) and radio relay systems. However, there is an immense broadband requirement due to high transmission data rate services and the data intensive applications that have to be provided in the operational area. However, transponder capacities on satellite payloads will remain a bottleneck.

In most areas in which forces have been engaged recently there has been little local communication infrastructure, either because it has never existed or because it was destroyed. Therefore, there is a great demand for highly mobile, flexible, reactive and adaptive networks and miniaturized, low energy consumption devices. Although today's state-of-the-art RF and information technology makes it possible to utilise such equipment, they need to be interoperable with the vital backbone of tactical information supply—Tactical Data Links.

For military systems 'in orbit', UAS RF, radio communication payloads and the like need to be small, lightweight, exhibit low energy consumption, etc., so that they can be accommodated on board. Radio links and networks also have to be extremely reliable and sustainable, with intelligent network management, not only to guarantee seamless operation (hand-overs), but also to provide autonomy in case of a temporary command and control blackout.

Communication technology also needs to evolve in the areas of Engage and Protect. It is evident that Information Warfare/Electronic Warfare has become a key instrument for military commanders. Although most attention is given to the sensor domain (SIGINT/ELINT, ESM and ECCM), there is also the vital need to protect communication links and assets, or to engage against such assets (e.g. C-RCIED).

Last but not least, it is worth mentioning a specific type of non-lethal weapon: namely, high power microwave (HPM) weapons, which can disable adversary information systems and power supplies and stop moving vehicles, etc., without collateral damage and human losses.

R&T trends of defence MW and RF technologies
As has been mentioned, new capabilities require the introduction of specific R&T programmes and projects to fill the technological gaps that have been identified. Because of the lessons learned from joint military operations and certain limitations of existing MW and RF defence technologies, the typical trends and targeted solutions do not differ significantly among countries and regions where R&T is most advanced (US, Europe, Russia, China and Israel). Table 1 gives illustrative examples of US and EDA initiatives that address the same or similar technology objectives. The US and Europe hold very strong positions with regards to MW and RF technologies and their world-leading roles seem unquestionable.

In Europe, the EDA, together with the experts from its Member States, has played a significant role in establishing the European Defence Research and Technology (EDRT) Strategy, which identifies what defence technologies should be developed ('Ends') and what actions ('Means') need to be taken to achieve those 'Ends'. Governmental experts in the relevant technical groups, called CapTechs, which are under the overall management of the Agency, have established a list of key technologies and skills within the 22 priorities ('Ends').

Focusing on the EDRT Strategy, all CapTechs were instructed by the EDA Steering Board to develop the corresponding Strategic Research Agendas (SRA), which will reflect the shared vision of both governmental and industrial experts on the most urgent technical challenges. The SRAs will not only respond to the actions defined by the EDRT Strategy and encourage the necessary push in technology, but will also take into account the required capabilities. The 'Ends' of the EDRT Strategy and SRAs under development in the CapTechs reflect the viewpoints of a wide range of European technology experts, and consequently can be considered as main technology trends.

For instance, in the area of RF sensors, efforts for the detection, localisation and identification of difficult targets in complex environments are focussed on increased sensitivity, improved clutter rejection and enhanced jamming suppression. These efforts include both the comprehensive development of generic technologies (system concepts and architectures, signal and data processing, platforms and integration, control and operation, and design and production) and main hardware components (transmitters, receivers, antennas, amplifiers, filters, converters, etc.)

Adaptive, self-learning and anticipative technologies for dynamically changing operational situations and various environmental conditions will enable defence forces to operate such RF sensors as radars without the direct involvement of human operators. To achieve this objective, more investment needs to be directed towards wideband antennas, waveform generators, power amplifiers and wideband high dynamic range receivers, and most importantly, new signal processing techniques.

Developments cannot stop at the component level, however. It is also vital to acquire greater knowledge regarding adaptive sensor management, the prediction of target behaviour and intent, software controlled sensors, dynamic frequency management, co-existence and effective interference suppression of RF systems and adaptive beam forming. More intelligent and efficient multisensory and networking technologies are needed in order to provide a more accurate common operational picture, improve reconnaissance, surveillance and target acquisition capabilities, and enhance the survivability of RF sensors.

Improvements must include the comprehensive development of bi-multistatic, active-passive RF sensors, generic technologies (system concepts and architectures, waveform generation, signal and data processing, platforms and integration, control and operation, design and production) and all the main hardware components (transmitters, receivers, antennas, amplifiers, filters, converters, etc.).

In the RF domain it is worth mentioning technology trends such as:

• Multifunction, scalable, modular, open systems and networks
• Active Electronically Scanned Array (AESA) antenna design and manufacture
• Low cost, mass, volume, power consumption and maintenance technologies
• Technologies for high confidence and all weather non-cooperative target recognition
• Simulation and modelling (highly accurate) for design, specification and performance assessment
• ESM techniques in dense signal environments, in particular emitter identification and high accuracy geolocation
• HPM weapons

In the communication domain the use of commercial off-the-shelf (COTS) products is beneficial both to saving time and reducing the spending budget. Civilian radio communications and IT services continue to be developed over short innovation cycles. However, due to the constraints prevalent in crisis operations, many COTS technologies and products still require a military add-on to be suitable for defence purposes.

With regards to Satcom technology, satellite payloads will operate in the EHF frequency range in order to achieve broader bandwidth and higher capacity. They will have more sophisticated features such as broadband switching techniques. Their antennas will be electronically controlled (beam forming) and thus adaptive and agile. A smart ground segment with automatic (re-)configuration capabilities will take care of networking functionality, which cannot be accommodated by the satellite payload. To keep military forces connected regardless of the constraints of the electronic environment (poor footprint, jamming, etc.) it is most important to implement a robust waveform.

As for the new tactical radio technologies, up to now, even digital radios have had to be developed individually for each category of use and assigned part of the spectrum (e.g. HF, VHF and UHF). In an international engagement scenario a command cell may require a dozen different radios to be set up and collocated. Software-defined radios (SDR) should have a robust software generated waveform and broadband antenna technology, enabling them to integrate the functionality of a series of different single radios. Various examples of SDRs are shown in Figure 2.

Web services, service oriented architectures and sophisticated IT security features should be implemented down to the tactical level. To cope with the resources needed in terms of bandwidth, studies are being conducted into high data rates (HDR) for tactical radio and cognitive radio for optimal exploitation of the spectrum, especially with regards to stressful electronic environments (dynamic spectrum management).

The demand for services even under highly mobile and electronically hostile conditions is defining new benchmarks for networking performance with commercially available standards like WiFi being adapted to military requirements. A Tactical Wireless LAN will have extended ranges and a robust waveform. In order to maximise individual network access, Body Area Networks aim to integrate any electronic device carried by the soldier (e.g. sensors, command and control).

The network layer has to be interfaced with service architectures like Service-Oriented Architecture (SOA), for tactical infrastructures such as radio networks and Tactical Data Links, and to a secure, intelligent network management system, which is disruption tolerant, fast (re-)configurable and can manage Quality of Service as dictated by the specific applications. The use of common standards for architectures and interfaces (in the RF, network and application domains) can significantly reduce lifecycle costs.

On the RF and MW components level it is first worth mentioning that AESA architectures use thousands of modules and few receivers. The main objective then is to decrease the number of modules and increase the reliability of AESA architectures. In the long term it is expected that AESA will be wideband, multifunctional and use a large number of receivers. Also, new ESM equipment requires higher sensitivity and probability of intercept of AESA, operating on new frequency bands in dense electromagnetic environments.

With regards to materials and technologies, Gallium Nitride (GaN) High Electron Mobility Transistors (HEMT) are the next generation of RF power transistor technology that offers the combination of higher power, higher efficiency and wider bandwidth than GaAs and silicon (Si)-based technologies. However, many long-term issues still have to be considered: high thermal conductivity materials and related packaging and assembly technology for adequate management of very high power solid-state components.

GaN-based receiver chain capabilities in S-band for radar applications and devices on free-standing or large GaN substrates will have to be developed as well as new composite substrates such as GaN on poly silicon carbide (SiC), where the surface material constitutes the best base for low cost epitaxies. The goal is to get reproducible structures with fewer defects and to demonstrate high quality devices with the high yield associated with high reliability.

Future wireless applications will require high performance and ultra low power consuming electronics. For that very reason materials and device architectures other than conventional silicon CMOS must also be investigated. As more and wider frequency bands are used in the future, the dimensions of all RF and MW modules will have to be very small, requiring the development of new 3D packaging and miniaturization technologies.

European R&T collaboration
One of the four main functions of EDA is to promote the defence R&T by the establishment of international collaborative programmes and projects. The cumulative budget of the EDA R&T programmes and projects, in respect of the current portfolio, is between €50 and €130 M a year; approximately 40 to 50 percent of that amount is invested in RF and MW technologies.

The number of ongoing projects in the three most concerned CapTechs (Components IAP1, RF Sensor Systems IAP2, and Communication and Information Systems IAP4) is also considerable, with usually 20 to 25 projects running in parallel. Obviously, this article cannot give a complete overview of all EDA RF and MW programmes and projects, but the following illustrative examples may give readers some idea of how the EDA is addressing current technological needs.

Since the mid-nineties, defence has been interested in GaN technology because of its high power density, robustness and linearity, in particular for such microwave applications as radars, EW equipment and multifunction systems. For that very reason the EDA launched two projects in recent years. The KORRIGAN project, which has been completed, developed a stand-alone European supply chain and capability for GaN technology, providing all major European defence industries with reliable state-of-the-art GaN foundry services for micro-electronic components and devices. The integration of KORRIGAN MMICs is shown in Figure 3.

As a result of KORRIGAN the second project, MANGA, was launched to further develop GaN technology. The main objective of the three and a half year programme is to build an independent European supply chain for the cost-effective processing of 100 mm SiC substrates and GaN HEMT epitaxial wafers. MANGA will mitigate the risk of export restrictions from the US on SiC substrates/GaN HEMT epitaxial wafers, demonstrate the European industrial capability for the supply of competitive and state-of-the-art SiC substrates and GaN HEMT epitaxial wafers, and develop a capability to supply SiC substrates and GaN epitaxial wafers to meet European defence needs.

MANGA will strengthen the European industrialisation and supply chain of the GaN HEMT transistors/MMIC technology, and support the development of next generation high performance radar, communication and electronic warfare components and system technologies.

Also concerned with materials technology is the Technology for HIgh speed Mixed Signal circuits (THIMS) project, which is at a stage where the contributing member states are close to finalizing the Technical Arrangement. THIMS will demonstrate the accessibility of the European defence industry to state-of-the-art SiGe technology in a secure, cost-effective way, and ensure that all design tools for mixed-signal designs are in place. The project will assess the limits of the currently available technologies, and quantify the benefits of implementing the next generation of technology in order to encourage availability within Europe.

Software-defined radio has been on the EDA's agenda since 2006, with the focus on the standardization and certification of SDR products. The results of the studies on 'Software defined and Cognitive Radio as well as spectrum management for European Defence' (SCORED) and on 'Wireless Interoperability for Security' (WINTSEC) are forming the background for the future development of SDR technology for military and civilian security users and providing the basis for interoperability.

The SCORED project was carried out by a consortium of 20 European companies and research organisations. Its objective was to provide a vision of current SDR issues from a military perspective, analyse the added value of the technology and provide an industrial view on its possible evolution at a European level. Follow-on programmes will implement SDR technology reference systems and demonstrators.

As part of the Joint Investment Programme on Force Protection (JIP-FP), the Wireless rObust Link for urban Force operations (WOLF) project will provide innovative solutions in order to increase "Wireless & robust communication" and "Information processing & situation awareness" capabilities, with a view to the survivability of such systems in operation.

Another JIP-FP initiative is the Intelligent Control of Adversary Radio-communications (ICAR) project, another JIP-FP offspring, which relates to the reliable selective prevention, control, capture and blocking of adversary mobile communications in multi-path environments such as urban or mountain areas. It aims to define an affordable, complete and integrated response for intercepting, localizing monitoring, and selectively blocking the threats at the radio interface that current and new mobile radio-communication technologies face.

Demonstrating European cooperation, experts from Italy, Belgium, Finland and France involved with Enabling Technology for Advanced Radio in Europe (ETARE), are studying advanced waveform technologies (ad hoc networkability, high throughput) that could be used for future operational waveform definition, at national or multinational level in Europe. These technologies will enable the development of future operational High Data Rate Networking (HDRN) waveforms.

The High Data Rate Technology for HF Communications (HDR-HF) project was contracted in 2009 and is jointly funded by Germany, Belgium and France. The project will develop and validate the concept of a Very High Data Rate (VHDR) communication in the HF band, providing a cheaper alternative to Satellite Communications solutions for long-range data communication.

Cognitive Radio has the potential to provide more flexible use of spectrum, enabling systems to adapt to their context while maintaining performance (e.g. robustness, availability, QoS). The Cognitive Radio for dynamic Spectrum Management (CORASMA) project, involving France, Italy, Poland, Portugal, Sweden, Belgium and Germany, aims to study the application of Cognitive Radio for military applications and assess its benefits.

Launched last year, the Signal Processing for Radar and EW Systems (SPREWS) project will identify and develop new solutions to increase the effectiveness of radar target detection, positioning, imaging, classification and identification in severe clutter, EW and propagation environments.

This year the Technology Enablers for Light & Low cost Urban RF Systems (TELLUS) project to investigate light, affordable and energy efficient radar and ESM systems has been launched.

The Scalable Multifunction RF (SMRF) programme and SMRF Implementation (SIMPLE) project will look into the development of technical architectures for multifunction, scalable, modular, open systems and networks.

Finally, the International Technology Partnership (ITP) on Studies for Integrated Multifunction Compact Lightweight Airborne Radars and Systems (SIMCLAIRS) was launched in 2009. At €25 M it is one of the highest value RF projects in the history of the EDA, aimed at developing a new generation of UAS and missile payloads based on synthetic aperture radar, while fulfilling the extreme mass, volume power consumption requirements posed by such platforms as UAS and missiles.

Conclusion
The military/defence sector is constantly evolving. Over recent years the very nature of the threats being faced, the arenas they are being fought in, etc., have changed considerably. Also, the economic downturn has forced budgetary constraints on governments and made it necessary for individual companies, universities and research establishments to seriously consider the cost and payback of ongoing or planned projects.

Budgets may be tight, but homeland security and defence issues still have to be addressed and the RF and microwave industry/community has a significant role to play in developing efficient and cost-effective technology to combat threats, secure borders and safeguard citizens.

Technological development is ongoing across the military/defence spectrum at both the component and system level. There is significant activity in the field or RF sensors, the development of modern military communications networks, both in orbit and on the ground, the evolution and implementation of semiconductor materials and packaging, just to name a few.

More general common objectives are miniaturisation, greater efficiency, reduced power consumption, and the reduction of development and lifecycle costs. It is widely recognised that collaboration, on every level, is becoming increasingly important to provide the necessary structure, support and incentive for projects to be successful and achieve their goals.

This article has used the EDA as an example of the importance of establishing international collaborative programmes and projects and demonstrated the scope, level of international cooperation, and scale of technology being addressed by current projects. They are just examples of the extent of current activity, not only in Europe but across the globe, and reflect that, despite changing threats and financial constraints, RF and microwave R&T development is on the right wavelength.

After studying Engineering in Electrical Sciences at the Armed Forces University, Munich, Germany, Michael Sieber gained a Tactical and Technical Leadership Training qualification from the German Army Schools. His employment has included: Combat Data Systems Engineer, Directorate for Maritime Combat Systems, Department of Defence, Ottawa, Canada, Deputy Director, International Armaments Affairs, Ministry of Defence, Bonn, Germany, and Chief, Information Acquisition Division, Technical Centre for Information Technology and Electronics, Greding, Germany. Sieber took up his current post as Assistant Director Research & Technology, European Defence Agency, Brussels/R&T Directorate, in 2010.

Attila Simon studied at Zalka M·tÈ Military Technology College, Budapest, Hungary, and gained qualifications in Air Surveillance Radar Technology and Air Force and Air Defence Operations at Zr"nyi MiklÛs National Defence University, Budapest. He gained his MBA degree in 2004. Starting as a Lieutenant and reaching the military rank of Colonel in 2007, Simon began his career as Platoon Commander of Air Defence C2 System/2nd Air Defence Radar Battalion, Air Force Base, Tasz·r, and held various military posts before becoming taking up his current role as Technical Project Officer for Radiofrequency Sensor Systems & Signal Processing, European Defence Agency, Brussels/R&T Directorate, in 2007.