12-2018

RF & Wireless signal

RF & Wireless signal through the data file reader in which the recorded or other custom data can be easily used. VSS provides the simulation and model capabilities to refine the radar architecture, implement increasingly accurate channel models (including multi-path fading and ground clutter), and develop performance specifications for the transceiver link budget and detailed antenna radiation pattern requirements. Figure 7: Multi-band, multi-range FMCW digital beam-forming ACC radar The plots in Figure 6 show several simulation results, including the transmitted and received chirp waveform, the antenna radiation pattern, and several system measurements, including the relative velocity and distance. In this simulation, the distance to the target is swept to reflect a vehicle that approaches and passes by a stationary radar, resulting in Doppler frequency that reverses the sign from negative to positive (red curve) and produces a null in relative distance as the target passes by the radar. In an automotive radar for ACC, the velocity and distance information would be used to alert the driver or take Figure 8: Edge-coupled single patch antenna optimized for center return loss and broadside gain 62 hf-praxis 12/2018

RF & Wireless Figure 9: 8 x 16 patch antenna array (128-element) with corporate feed (single-feed port) corrective action (such as applying braking). Multi-Beam/ Multi-Range A typical ACC stop-and-go system requires multiple short and long-range radar sensors to detect nearby vehicles. The shorter range radar typically covers up to 60 m with an angle coverage up to ±45°, allowing the detection of the vehicle’s adjacent lanes that may cut into the current travel lane. The longer-range radar provides coverage up to 250 m and an angle of ±5° to ±10° to detect vehicles in the same lane, further ahead. To support multiple ranges and scan angles, module manufacturers such as Bosch, DENSO, and Delphi have developed and integrated multi-range, multi-detection functionality into increasingly capable and cost sensitive sensors using multi-channel transmitter (TX)/receiver (RX) architectures. These different ranges can be addressed with multi-beam/multi-range radar by employing radar technology such as FMCW and digital beamforming with antenna array design. Antenna A multi-modal radar for an ACC system [2] based on an FMCW radar driving multiple antenna arrays is shown in Figure 7. This multi-beam, multi-range radar with digital beam forming operates at both 24 and 77 GHz, utilizing two switching-array antennas to enable long range and narrow-angle coverage (150 m, ±10°) and short range and wide-angle coverage (60 m, ±30°). This example illustrates the use of multiple antennaarray systems, including multiple (5 x 12 element) series-fed patch arrays (SFPAs) for long range, narrow-angle detection (77 GHz), a single SFPA (1 x 12 elements designed for 24 GHz) for short, wide-angle detection, and four (1 x 12) SFPAs for the receiver that were required for this type of system. 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 TR/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 Ohms 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 NI AWR Design Environment platform includes AXIEM 3D planar and Analyst 3D finite element method (FEM) Figure 10: Series feed 1 x 8 patch array with parameterized modifiers hf-praxis 12/2018 63