W-Band Low-Profile Transmit Array Based on Wideband Partially Reflecting Surface

This communication presents a wideband low profile transmit array (TA) with a small height-to-diameter (H/D) ratio of 0.285 working at a center frequency of 100 GHz, which consists of a waveguide feed source, a metal ground plane, a partially reflective surface (PRS), and a transmission surface (TS). A PRS with not only a positive reflection phase gradient, but also a negative transverse reflection magnitude gradient is designed above the ground plane to reduce the height as well as to broaden the bandwidth of the TA. The proposed TS is composed of eight unit cells (UCs) with a high transmission magnitude and phase differences of 45 degrees in a broadband range. Four passive antenna prototypes with different beam directions are fabricated to validate the design concepts, and good agreements are obtained between the radiation patterns, gain curves, and return losses. The measured peak gain is 20.7 dBi with aperture efficiency (AE) of 10.5% at 99.5 GHz. A relative bandwidth of 15.2% is obtained within 3 dB gain variations, making it a promising candidate for sixth-generation (6G) wireless communication applications.