AWR Application Notes

mmWave Automotive Radar and Antenna System Development Using AWR Software 7 www.cadence.com/go/awr Radar performance is greatly influenced by the antenna technology, which must consider electrical performance such as gain, beam width, range, and physical size for the particular application. The multiple, fixed TX/RX antenna arrays in the example radar were optimized for range, angle, and side-lobe suppression. A patch antenna is relatively easy to design and manufacture and will perform quite well when configured into an array, which results in an increase of overall gain and directivity. The performance of a rectangular patch antenna design is controlled by the length, width, dielectric height, and permittivity of the antenna. The length of the single patch controls the resonant frequency, whereas the width controls the input impedance and the radiation pattern. By increasing the width, the impedance can be reduced. However, to decrease the input impedance to 50 Ω often requires a very wide patch antenna, which takes up a lot of valuable space. Larger widths can also increase the bandwidth, as does the height of the substrate. The permittivity of the substrate controls the fringing fields with lower values, resulting in wider fringes and therefore better radiation. Decreasing the permittivity also increases the antenna's bandwidth. The efficiency is also increased with a lower value for the permittivity. Designing a single patch antenna or array is made possible through the use of design software that utilizes EM analysis to accurately simulate and optimize performance. The AWR Design Environment platform includes the Cadence AWR AXIEM ® 3D planar and Cadence AWR Analyst™ 3D finite element method (FEM) EM simulators. These simulators not only simulate antenna performance such as near- and far-field radiation patterns, input impedance, and surface currents, they also co-simulate directly with AWR VSS software, automatically incorporating the antenna simulation results into the overall radar system analysis without the need to manually export/import data between EM simulator and system design tools. Both the AWR AXIEM and Analyst simulators take the user-defined physical attributes of the antenna such as patch width and length, as well as the dielectric properties such as material and substrate height, to produce the electrical response. The AWR AXIEM simulator is ideal for patch antenna analysis (Figure 8), whereas the Analyst simulator is best suited for 3D structures such as modeling of a coaxial feed structure or finite dielectric (when proximity to the edge of a PCB would impact antenna performance). Figure 9 shows a patch antenna array with corporate feed and 167K unknowns solved in less than 6.5 minutes with a quad core. Figure 8: Edge-coupled single-patch antenna optimized for center return loss and broadside gain Figure 9: 8x16 patch antenna array (128-element) with corporate feed (single-feed port) Optimization

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