Some years ago CST introduced a frequency domain solver into CST MICROWAVE STUDIO® (CST MWS) in addition to its time domain solver. The company recognized that an ever increasing array of microwave/RF and high speed data applications required alternate solver technology in order to optimize speed and memory usage. While such technology was available from various vendors, CST’s approach placed the solvers within the same user friendly front-end that many engineers were already familiar with.
The company has continually expanded the range of technology available and increased the vast number of RF, microwave and high speed applications that can be solved quickly and accurately. Non-EM physics has also been introduced with circuit, thermal and mechanical simulation all available and closely coupled either directly or through CST DESIGN STUDIO™ (CST DS).
In the new CST STUDIO SUITE 2010 the circuit and system simulator CST DS, including optimization and layout, is a standard feature of all licenses. Full system simulation with CST tools is now emerging as a mainstream task for the design engineer—a breakthrough in a world of compact, high frequency devices with multi materials, antennas and circuits all within the same housing.
With such complete technology, CST can offer ideal solutions. For example, the data networking company may appreciate just the time domain solver for its broadband capabilities and memory efficiency for complex devices, but the defense contractor may additionally need the frequency domain solver for phased-array antennas and the asymptotic solver for electrically large aircraft.
While advancing the solving technology, CST has recognized that engineers often have large software toolboxes comprising mechanical CAD, layout, circuit simulation, legacy EM and more. A stand alone or ‘point tool’ EM simulator is no longer sufficient; it has to fit into existing workflows. This article reviews the latest 3D EM technology in CST STUDIO SUITE 2010 and how it has become a vital component in so many design workflows and system simulations.
Additions to core solvers
While the core solvers remain time-domain (T) and frequency-domain (F), these are constantly being enhanced, driven both by new algorithm research and high performance hardware. New in the F solver for version 2010 is sensitivity and yield analysis where S-parameter ranges for tolerant parameters can be calculated efficiently without numerical recalculation.
Also for the F solver, third-order elements and mixed elements are allowed. This combination is ideal for applications requiring frequency domain simulation that are electrically large but that also have critical small features. For the T solver, Nth order material fitting is new and allows accurate broadband modeling of critical material properties. Improved handling of port losses at broadband ports increases accuracy for certain applications.
The acquisition of the EM division of Flomerics has brought an additional approach to time-domain via the transmission line matrix method (TLM). This approach to 3D EM has strengths in EMC/EMI applications and installed antenna performance. One of its key benefits is its ‘compact model’ library, whereby geometrically complex components, such as vents and seams (including curved models for version 2010) that are difficult to mesh, are replaced by accurate circuit representations. Its ‘octree meshing’ approach is very efficient for structures with large differences in detail.
For version 2010, CST MICROSTRIPES™ (CST MS) is further integrated into CST STUDIO SUITE allowing easy model exchange and, key in this release, integration with CST DS. As with CST MWS, this allows CST MS blocks to be placed in the system simulator with circuit components or cascaded. CST MS also now benefits from the import of broadband sources from CST PCB STUDIO™ (CST PCBS) or CST CABLE STUDIO™ (CST CS).
This allows the results of PCB or cable harness simulations to be placed inside an enclosure and then simulated with CST MS to give the complete radiated emissions response. This decoupled approach leverages the strengths of both tools, allowing systems with components on vastly different scales to be simulated in a reasonable time. This approach is also available between other members of CST STUDIO SUITE via the ‘field source’ monitor.
Accelerating the simulation
Figure 1 CST Studio Suite HPC options.
In recent versions, techniques for ensuring that available hardware can be fully exploited to speed up simulations have been introduced. High performance computing (HPC) platforms can be used to achieve dramatic speed-ups.
To consolidate the many acceleration features now available through hardware and HPC, CST has introduced ‘acceleration tokens.’ One token will enable access to all acceleration features, but on limited hardware. More tokens will allow greater hardware utilization.
Examples of acceleration features include GPU cards (graphics card technology), MPI (using a computing cluster) and port/frequency point/parameter distribution (sending directly parallel tasks to multiple machines). For version 2010 the multi-CPU option becomes a standard feature where utilization of up to 16 threads is allowed on one main board. Figure 1 shows HPC features available.
New Solver Technology
Despite recent advances in hardware capability, certain applications are still too demanding for the core general-purpose solvers. Particularly challenging problems range from complex multi-layer PCBs to large aircraft or ships. In either case, the complexity or size of the required solution mesh means that alternative techniques must be sought to achieve reasonable simulation times.
There are also physical consequences of driving high frequency currents or fields through devices, in particular heating and mechanical stress. To fully realize complete system simulation, these effects need to be considered in the system design.
Figure 2 Antenna installed beneath an Apache helicopter. Inset shows the meshed biconical antenna.
In recent versions an integral equation solver (I) was introduced making use of the method of moments (MoM) and multi-level fast multipole method (MLFMM). This has proved successful for large antennas and aircraft. Figure 2 shows installed performance simulation of an antenna radiating at around 9.5 GHz. This corresponds to an electrical length of the helicopter of ca. 600 wavelengths. However, the simulation of electrically huge (thousands of wavelengths) operational aircraft and ships at radar frequencies requires other approaches.
CST’s new asymptotic solver uses the recently developed shooting bouncing ray (SBR) method, an extension to physical optics (PO). The technique employs a second- order curved surface mesh that avoids mesh singularities. Very high accuracy and correlation to full wave solver results (within full solver limits) is being observed for a wide range of examples.
CST PCBS was introduced in CST STUDIO SUITE 2009. With a very easy to use ‘layout’ type interface familiar to PCB designers, the software is able to import and quickly calculate S-parameters of nets in PCBs up to four or so layers. CST PCBS links to CST DS for larger overall system simulation. In version 2010 a technique able to solve much more complex PCBs and obtain output power delivery network (PDN) input impedances is introduced.
Figure 3 Imported PCB for power integrity analysis.
This is a 3D FEM frequency domain-based method that is able to identify dominant EM effects from the PCB structure. Complexity is reduced by applying selective EM models in critical parts and replicating these through the structure. The 3D (FE FD) solver is based on the frequency-domain finite-element method, combined with a domain-decomposition approach. Problem-adapted basis functions are used to improve simulation performance by exploiting the structural characteristics of the PCB. Figure 3 shows a screen shot of CST PCBS.
Also in version 2009, CST CS was introduced, allowing full cable harness simulation inside and outside chassis structures. Fully integrated with CST DS, it is a major piece of the system simulation puzzle allowing cable radiation (or irradiation) to be taken into account. For 2010, a number of enhancements are introduced including a direct link to the 3D modeler. The illustration at the beginning of this article shows a vehicle and cable harness simulation in CST CS.
Figure 4 The multi-physics analysis of a cavity filter (courtesy of Spinner GmbH).
CST MPHYSICS STUDIO™ incorporates the existing thermal solver with a new mechanical stress solver. This combination allows currents generated from an EM simulation to be used as a heat source, which in turn can be used for mechanical stress analysis. To complete the loop, the deformation arising from the mechanical stress can be fed back for sensitivity analysis. Figure 4 shows progressive field, thermal and mechanical simulations for a cavity filter.
Pre- and post-processing
Advanced modeling capabilities such as bending sheets to create conformal layers and interactive transformations have been successfully used in applications such as smart phone and RFID simulation since being introduced at the end of 2008. In version 2010, some key features enhancing usability for the most complex of structures are added. This includes full hierarchical component assemblies maintained from CAD assembly imports, a continuity (connectivity) checker for the hexahedral mesh. The continuity checker is ideal for verifying that EDA trace imports are electrically connected. It can also be used to check for unintended short circuits.
Layout and mechanical imports have further been extended in version 2010 so that virtually all commercial and interchange formats are covered. In addition to existing Mentor, Zuken and ODB++, direct import of Cadence .brd and .mcm files is now possible through an advanced import filter. With a look and feel familiar to layout engineers, this filter allows interactive selection of areas and traces, stack-up editing and component placement, all before the 3D model is created. An ‘EDA token’ can now be purchased to access all aforementioned imports.
On the post-processing side, sensitivity analysis is introduced as described earlier. Farfield processing has also been consolidated and improved. For visualization of fields and current on the largest structures a new plotting engine is incorporated, which gives significantly improved graphic performance.
Building even further on the complete technology theme, CST STUDIO SUITE 2010 enhances existing solvers and introduces completely new ones for the most demanding of applications. It leverages high performance computing to offer excellent solution turnaround times. With new coupled physics solvers, greater integration of all modules and greater interoperability, the software will allow engineers to consider full system simulation before entering the test lab.
RS No. 302