Automotive radar applications, such as intelligent cruise control (ICC) and collision-avoidance radar, require highly directional antennas. These antennas must have the capability to distinguish targets in a predetermined field-of-view (FOV). Printed antenna arrays are a preferred choice, but they can have large feed network losses. In addition, the antenna array’s weight may produce cracks in the solder balls upon circuit integration. The free-space beam-forming technique can eliminate feed network losses and improve antenna performance at millimeter-wave frequencies and higher. The transmit-array is one form of this technique. To demonstrate its capability, researchers from Singapore developed a 77-GHz dual-layer transmit-array for automotive radar applications.
The researchers designed the transmit-array by etching coplanar patch unit-cells on opposite sides of a printed-circuit board (PCB). Four high-gain beams are generated by combining the transmit-array with four substrate-integrated waveguide (SIW) slot antennas, which serve as the primary feeds. Computer Simulation Technology (CST) Microwave Studio was used to simulate the unit-cells. A test fixture was designed to hold and align both the SIW slot primary feeds and the coplanar transmit-array. The test equipment used to perform measurements included a customized Cascade Microtech probe station and an E8361A network analyzer from Keysight Technologies. The measured gain of the coplanar transmit-array antenna prototype was 18.5 dBi for the ports at 76.5 GHz, demonstrating agreement with the simulated results.
See “77-GHz Dual-Layer Transmit-Array for Automotive Radar Applications,” IEEE Transactions on Antennas and Propagation, June 2015, p. 2,833.