Highly Directional Wideband Transmitarray for 79 GHz Band Radars

This paper presents a novel design and implementation of a highly directional wideband transmitarray (TA) antenna for 79 GHz radars. A novel method of using slot coupling between the receiving patch and transmitting patch is utilized for achieving wideband transmission phase. Compared to the traditional TA using slot coupling receive-transmit patch antenna unit cells, low profile of only four conducting layers are used. In addition, wide transmission bandwidth of 18.6% is achieved for the proposed unit cell. To realize a 3-bit phase delay, the distance between coupling slots and length of phase delay line are elaborately adjusted. Finally, to realize a highly directional radiation with the half-power beamwidth ≤3° in E-plane and H-planes, a TA antenna with circular aperture of 1976 unit cells was designed and measured. The measured results prove that its HPBW in E-plane is 2.8°, and in H-plane is 2.9°. In addition, it is observed a high aperture efficiency of 28% and a 2 dB gain bandwidth of 75-85 GHz can be achieved for the presented TA antenna. This TA antenna has been successfully implemented into commercial radar systems for obstacle detection and safe operation in applications of passenger vertical lift systems, such as elevators, lifts, etc., at China.