Beam Switching mm-Wave STAR Metasurface Array for Bidirectional Satellite Relay Communications

This paper presents a low-complexity, high-gain beam-switching simultaneous transmission and reflection (STAR) metasurface array for millimeter-wave bidirectional satellite relay communications. The proposed STAR metasurface unit cell consists of an end-loaded dipole on the top layer and a slotted end-loaded dipole on the bottom layer, enabling simultaneous phase and amplitude manipulation in both transmission and reflection modes. A compact 4.48λ₀ × 4.48λ₀ metasurface array operating over 27–29 GHz is designed, fabricated, and experimentally validated. The array is spatially excited using a reconfigurable antipodal Vivaldi antenna integrated with PIN diodes to realize dynamic beam switching in the azimuth plane. Experimental results demonstrate bidirectional beam scanning from −30° to +30° in both transmission and reflection regions, providing an overall angular coverage of 120°. The proposed array achieves peak gains of 17.5 dBi in transmission mode and 16.5 dBi in reflection mode at 28 GHz, with scan losses below 1 dB and aperture efficiencies of 22.5% and 19.8% in transmission and reflection modes, respectively. By utilizing only three PIN diodes, the proposed design significantly reduces switching complexity, biasing circuitry, and power consumption compared with conventional phased-array and reconfigurable metasurface approaches. Owing to its low-profile structure, high gain, wide angular coverage, and efficient bidirectional beam-switching capability, the proposed STAR metasurface array is well suited for next-generation satellite relay links, non-terrestrial networks (NTNs), and millimeter-wave communication systems.