Reconfigurable Bidirectional Metasurface Antenna Based on Anisotropic Meta-Element for Millimeter-Wave UAV-Assisted Two-Way Relay Communication

This letter presents a reconfigurable bidirectional metasurface (BDMS) antenna with polarization-dependent switching of reflection (R)/ transmission (T) modes. Initially, a low-profile anisotropic meta-element is designed with a primary focus on polarization-dependent dual functionality. Subsequently, a 1-bit quantized phase modulated BDMS is designed and spatially excited by an Antipodal Vivaldi Antenna (AVA) from a calculated focal distancefof 21 mm. The switching between R-mode and T-mode is achieved by mechanically rotating the AVA by 90° and thus the proposed BDMS antenna achieves independent beamforming in backward and forward direction, respectively. The proposed BDMS enhances the performance of AVA achieving a practical peak gain of 21.5/20.2 dBi with a gain enhancement of 15.3/14.1 dB and an aperture efficiency of 25.1/18.6% in R-/T-mode, respectively, at 28 GHz. Also, a practical 3-dB gain bandwidth of 15.6/13% in R-/T-mode is realized. The proposed BDMS antenna facilitates wideband beamforming at millimeter-wave fifth generation (5G) band and is suitable for UAV-assisted two-way relay communication in space-air-ground integrated networks (SAGIN) application.