Compact Wideband Circularly-Polarized Mechanically Beam-Steering Antenna for Ka-Band Vehicular Communications

The stable vehicular space-air-ground integrated network (SAGIN) requires high-gain multi-beam/beam-steering antenna systems. In this paper, we propose a compact high-gain wideband circularly-polarized (CP) beam-steering antenna with novel rotatable phase-gradient metasurface (PGM) transmitarrays for the SAGIN. It consists of a novel substrate-integrated-waveguide (SIW) array feed and three innovative metasurface transmitarrays (M-0, M-1, and M-2), capable of providing any compensation phases between 0 degrees and 360 degrees. The novel PGM unit cells have two identical CP U-slot patches that perform CP-to-CP conversions with high transmission efficiencies. In addition, a new and accurate beam-steering analytical formulations are proposed for fast predictions of scanning angles. Experimental results show that the proposed compact SIW array feed achieves an aperture efficiency of 58.8%, a 3-dB gain bandwidth of 10.8%, and a 3-dB axial ratio (AR) bandwidth of over 23%. The proposed entire beam-steering antenna achieves a peak gain of 27.56 dBic, which corresponds to an aperture efficiency of 48.5%, and an exceptionally wide 3-dB AR bandwidth within the scanning range. It is a strong candidate for future millimeter-wave communications in satellite and radar systems and vehicular communications.