Microwave Journal

EDA Focus Nov. 2010: Exploring the Latest EM Simulation Technology.

November 15, 2010

Most high frequency engineers today recognize that electromagnetic simulation software plays a key role in the modeling and design of microwave and high speed electronics. The miniaturization, high-performance and integrated functionality of commercial and defense based modules and RFIC/MMICs are due largely to the engineering support offered by these tools. Just as the industry continues to improve products for our end-users, design software is also continually evolving. If you haven’t kept up with the advances in 3D EM simulation technology over the past few years, you may be un-aware of how much they have improved. Fortunately, a number of leading EM software vendors will be presenting webinars in December, which look at the state of the art in simulation technology, addressing important design issues and provided valuable tutorials on how to get the most from these tools. Here’s a look at what these various webinars have to offer.

The December webinar from ANSYS focuses on the new solver technology available in HFSS and should be of particular interest to designers of radar and electronic warfare systems. Ansoft has developed two new solvers for engineers working on large-scale electromagnetic problems. The HFSS v13 release introduces a new Transient Solver for time domain field calculations and the new Finite Element Boundary Integral (FEBI) boundary condition. This novel boundary condition (BC) can wrap around complex radiating structures; thereby removing large air volumes and providing a significantly faster solve time. As engineers are challenged with designing their components into ever smaller, arbitrary spaces (consider the iPhone antenna), simulating conformal surfaces are a common occurrence.

The new HFSS Transient capability is a 3-D full-wave transient electromagnetic field solver based on the discontinuous Galerkin method (DGTD), complementing the frequency domain technology (FEM) in the “standard” version of HFSS. The discontinuous Galerkin methods in mathematics form a class of numerical methods for solving partial differential equations. They combine features of the finite element and the finite volume framework and have been successfully applied to hyperbolic, elliptic and parabolic problems arising from a wide range of applications. Up to now, the methods have received considerable interest for problems with a dominant first-order part, e.g. in electrodynamics, fluid mechanics and plasma physics.

The tetrahedral finite element technique exploits the same automatic adapted-for accuracy meshing technology found in the original frequency-domain version. Engineers using HFSS Transient will now be able to investigate applications with short-duration pulsed excitations such as ground-penetrating radar, electro-static discharge, electro-magnetic interference and lightning. Other applications include time domain reflectometry (TDR) as well as field visualization from any general time-based input pulse.

The new Finite Element Boundary Integral or FEBI is a new technique for analyzing open boundary problems with HFSS. The new FEBI boundary condition can wrap around complex radiating structures; reducing simulation times by removing large air volumes from the calculation. This combination of HFSS finite elements for volumetric field calculations and HFSS-IE integral equations for ideal truncations of open boundary conditions allows antenna designers to solve large scale antenna, antenna placement and scattering problems with a high degree of accuracy and efficiency. These topics will be discussed in Dr. Matt Commens’ (ANSYS) webinar.

Introduced with version 12.1, HFSS-IE is an optional, add-on solver that uses the method of moments (MoM) technique to solve for the sources or currents on the surfaces of conducting and dielectric objects in open regions. HFSS-IE solver uses the Adaptive cross approximation (ACA) method in conjunction with an iterative matrix solver to reduce the memory and complexity requirements, allowing this tool to be applied to very large problems. Users can link HFSS designs as sources in an HFSS-IE design through a data link. The feed can be created in HFSS and then the fields from that simulation can be linked into the target HFSS-IE design with a few mouse clicks. As an additional feature, the user can also include the feed structure of the source simulation in the target HFSS-IE design and include its scattering in the final result. In combination with HFSS the design engineer can now pick the best solver to use for a given situation and in many cases can take advantage of both solvers in a linked project.

ANSYS Webinar Registration >>

With ANSYS expanding the types of solvers available in HFSS, the company is pursuing a technology roadmap not unlike their competitor CST, namely offering multiple solver types. As CST points out in their product literature “Just a decade ago, experts argued which technology would dominate the 3D EM simulation market: time or frequency domain?” Time domain has a reputation for solving problems with a large number of mesh cells, whereas frequency domain – using tetrahedral instead of rectangular gridding – often offered better geometry approximation. Where HFSS is now introducing Transient solvers and techniques for larger problems, CST has focused on developing multiple solver technologies while overcoming the disadvantages associated with the time domain’s staircase approximation. CST’s adoption of a multi-solver approach would seem to reinforce the belief that no one method is perfect for every application.

With this in mind, the company has developed frequency domain technology to complement their time domain solution as a general purpose solver. Today, CST promotes “Complete Technology for 3D EM”. The company offers customers a choice of six solver modules. In addition to the time domain solver in the company’s flagship product – Microwave Studio, modules based on methods including FEM, MoM, MLFMM and SBR are available, each offering distinct advantages in their own domains, enabling simulation reliability through cross verification. The webinar takes a look at these various solvers and the new functionality in CST’s latest offering of its product portfolio – bundled under the Studio Suite name – will be the topic of their webinar presentation. Studio Suite 2011 is the integrated design environment hosting an entire range of solver technology that includes: time domain, frequency domain, integral equation, asymptotic, fast resonant, eigenmode, static and stationary fields, charged particles, temperature, mechanical stress, and circuit simulation.

When software vendors talk about simulation performance, they are generally referring to capacity (the size problem that can be solved, often measured in number of unknowns); speed (the time required to arrive at a solution), and accuracy. The nature of today’s high frequency electronics is such that designers are continually developing larger and more complex devices, which in turn demands increased simulation performance.

CST’s introduction of Perfect Boundary Approximation [PBA]® technology into their Finite Integration Technique (FIT) solver allows a more accurate and efficient mesh of conformal geometries and thus represents a major breakthrough in extending the performance of Microwave Studio.

The standard FDTD staircase grid is pretty efficient for a large number of mesh cells, but it does have a major drawback when it comes to the geometrical approximation of arbitrarily shaped structures. In a convergence study, the achieved accuracy of a staircase model improves slowly and unsteadily and takes a large number of iterations. The geometrical precision achieved thanks to PBA enables smooth broadband convergence with a minimum number of passes. Tetrahedral meshing has more or less the opposite strengths and weaknesses of staircase meshing. PBA combines the advantages of both standard approaches and offers a superior solution for most applications. Thus the introduction of arbitrary order curved elements represents a major step forward in tetrahedral meshing technology.

CST will also present the recent developments in integrating the MICROSTRIPES product into STUDIO SUITE 2011. This solver technology is based on a multi-grid formulation of the time-domain Transmission-Line Matrix (TLM) method. The 3D model is automatically "discretized" enabling localized gridding around detailed geometric features and within dielectric/magnetic materials. CST MICROSTRIPES™ is well-known for its "compact modeling" technology. In EMC/EMI applications, objects with relatively small dimensions, such as slots/seams, vents, multi-wires, shielded cables, have a big impact on the performance of the system. Compact modeling enables these critical features to be represented by equivalent transmission-line models; it is not necessary to use a fine mesh to capture the small dimensions. Compact modeling can reduce the computer requirements by several orders of magnitude.

Another new feature in Studio Suite 2011 to be explored in this webinar will be the use of sensitivity information from the solvers to speed up optimization and yield analysis. Automatic optimization and sensitivity analysis are key requirements for designers and both of the general purpose electromagnetic solvers – time and frequency domain - of CST MICROWAVE STUDIO can provide sensitivity information for an arbitrary number of parameters in just one simulation run. Webinar attendee will see the newly implemented trust region framework in CST STUDIO SUITE 2011, which can employ the sensitivity information to cut down optimization time dramatically. Yield analysis for complex three dimensional models will also be available at virtually no additional computational cost.

CST Webinar Registration >>

Clearly, accurate simulations are a concern for designers as well as EM software providers. One aspect of accurate component characterization is the degree to which all factors influence electrical behavior have been accounted for. For instance, the electrical property of a piece of waveguide will depend on the physical dimensions of that waveguide, which will vary to some degree with temperature. Thus, the real world is inherently multi-physics. Electromagnetics, in particular, does not exist in isolation. Rather, other physical effects, like heat transfer and mechanical forces, can make a big impact on the performance of electromagnetic devices.

For this reason, R&D teams must consider adopting tools that let them innovate beyond the limited scope of traditional EM-only simulation. By considering all relevant physical effects in your designs, you can create computer models that give you the accuracy necessary to gain the competitive edge. The COMSOL Multiphysics simulation software environment facilitates all steps EM users expect in the modeling process − defining the structure geometry, meshing, solving, and then visualizing results. COMSOL’s emphasis on Multiphysics analysis starts with the versatility and powerful functionality users have to specify the physics. Model set-up is quick, thanks to a number of predefined physics interfaces for applications ranging from fluid flow and heat transfer to structural mechanics and electromagnetic analyses. Material properties, source terms and boundary conditions can all be arbitrary functions of the dependent variables.

Predefined multiphysics-application templates solve many common problem types. The user also has the option of choosing different physics and defining the interdependencies. Users can even specify their own partial differential equations (PDEs) and link them with other equations and physics. In this webinar, COMSOL will present the implementation of multiphysics simulation for electromagnetics, including a real-world example from guest speaker, Dr. Philippe Masson of the Advanced Magnet Lab.

Comsol Webinar Registration >>

EM Applications: Package and Component Modeling
Along with the opportunity to learn about all the new EM technology being introduced in December, engineers attending the Agilent Innovations in EDA series will get a tutorial on how to apply EM simulation (along with alternative methods of equivalent circuit models and measurements) to properly characterize advanced IC packaging and interconnects. RFIC, monolithic microwave integrated circuit (MMIC), high-speed IC or package system (SIP) are directly affected by the package (including wire and bead / welding bump) electrical characteristics. Previously, designers may have the 3D electromagnetic field simulation in a drawing and analysis tool focused on the package performance, separate from the tool used for circuit simulation. Static S-parameter results would then be imported back into the SIP IC circuit design environment for a comprehensive analysis. This design flow is both laborious and inaccurate. With the company’s products EMPro and Advanced Design System (ADS), engineers can design the system in the advanced (ADS) in combination with efficient 2D design layout to create three-dimensional packaging structure, thus simplifying the design process in the use of circuit simulation and realization of three-dimensional electromagnetic simulation of IC, package, substrate and module co-design.

This webinar looks at the big picture of developing the whole IC in package design, discussing not only the EM technology, but the design flow as it integrates with optimizing circuit performance.

Agilent Webinar Registration >>

Component modeling, the process of characterizing a passive devices' parasitic behavior is also the theme of our December Besser Associates webinar. While not specifically focused on EM simulation, this is an area where EM tools are frequently used. This webinar will take a look at the impact that passive parasitics play on overall circuit performance. This webinar is also sponsored by AWR, another software vendor with their own 3D EM simulator - Axiem. Therefore, we might consider that there are no less than five webinars on EM simulation in December. Happy Holidays.

Besser Webinar Registration opens 11/22 >>