CST – Computer Simulation Technology

Automotive Simulation Using CST MICROWAVE STUDIO

This article demonstrates the application of CST MICROWAVE STUDIO® (CST MWS) to the simulation of electrically large automotive structures. CST MWS is ideal for such applications since the geometry can be easily imported and modified using the powerful user interface. The accurate and robust PERFECT BOUNDARY APPROXIMATION (PBA)® is exploited, taking advantage of the linear scaling of memory with increasing mesh cells and allowing the simulation of broadband AM/FM, GSM and GPS antennas.

Other advantages include time-domain simultaneous excitation for mutual coupling analysis and nearfield and farfield calculations in the time (probes) and frequency domains (fields on curves). The farfield calculation over lossy grounds enables the simulation of outdoor test ranges. Accurate calculation and visualisation of 3D fields and surface currents useful for antenna and cable placement. Results and geometry data may be easily exported for use in third party or in-house tools....

Figure 1: Geometry of imported car and supported CAD import formats

A variety of CAD formats may be used to import the structure into CST MWS and these are shown in Figure 1 along with the geometry of the car to be simulated. In this case, the STL format was used.

Figure 2: Typical antenna structures and placements (AM/FM,GPS) and power cable setup (DC)

Figure 2 shows the various types of antennas that can be simulated with CST MWS demonstrating the versatility of the PBA and the THIN SHEET TECHNIQUE (TST) ™ for the correct modelling of small features such as thin-wire on-glass antennas and relatively thin power cables.

Figure 3: Full model including windscreen and on-glass wire antenna

The windscreen on-glass antenna highlights several significant features that are advantageous for such a simulation, namely, the ability to import curves of the antenna which can then be transformed into wires in CST MWS, the thicken sheet  feature to assign a thickness to an infinitely thin sheet such as the windscreen and also the possibility to actually model the finite radius of the wires. Figure 3 shows the on-glass antenna and windscreen components incorporated in the car model. The car model can be simulated with all of these features included without having to separately simulate parts of the structure. This is a consequence of the almost linear memory scaling with mesh cells and is, in conjunction with the PBA and TST techniques, a strong feature of the Time Domain solver.

Figure 4: 3D and Polar Farfield Patterns for various Antenna Types with and without car model present (green curves in the polar plots)

The effect of the car on the farfield patterns of some of the aforementioned antenna configurations is shown in Figure 4 where the 3D and polar plots of the farfield are shown for the frequencies applicable to the antenna simulated. The green polar curves are for the antenna simulations without the car present.

Finally, Figure 5 shows the model setup for a car with a harness signal or power cable. The surface currents for this power cable set up are also shown at DC. Using the combine results feature in CST MWS, all interference sources may be superimposed to obtain their global effect. The field along or at any arbitrary position on the curve may be evaluated and exported.

Figure 5: Cable Harness / Power cable definition and surface currents

The aim of this article is simply to demonstrate the impressive features required for the simulation of automotive antenna placement and EMC applications. CST MWS offers comprehensive CAD facilities to not only import structures but also to simplify and modify the model where necessary. This includes the ability to import wires which may either be treated as infinitely thin or finite radius wires. Broadband results are obtained in a single simulation with farfield monitors at any desired preset frequencies. Time Domain field monitors are also available. The Time Domain simulation delivers, in addition to the fourier-transformed frequency results, the time varying probe data for either nearfield or farfield data. In addition, automotive structures are gernally electrically large which are easily handled due to the almost linear memory-mesh cell scaling characteristic of the CST MWS Transient solver.

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