2026 Zhang Polarization Aware Rotatable Antennas

This paper investigates a dual-polarized reconfigurable intelligent surface (DP-RIS)-empowered symbiotic radio (SR) system with rotatable antennas (RAs). The objective is to mitigate the double-fading effect in RIS-assisted cascaded links by reconfiguring antenna orientations. A joint spatial-polarization design is proposed to exploit directional radiation gain and ensure polarization matching, which is crucial as antenna rotation alters local polarization and can lead to polarization mismatch. The methodology involves formulating a transmit power minimization problem that jointly optimizes digital beamforming, RA rotations, transceiver polarization states, and DP-RIS phase shifts subject to constraints related to primary and secondary rate requirements as well as interference temperature for non-SR users. An alternating optimization algorithm is developed to solve the non-convex problem, integrating semidefinite programming, difference-of-convex programming, and Riemannian conjugate gradient methods. Furthermore, two low-complexity RA designs, a subarray-wise shared rotation design and a discrete rotation codebook design, are proposed for practical deployment. Simulation results demonstrate that the polarization-aware RA design significantly reduces required transmit power compared to fixed-orientation and polarization-unaware benchmarks, while both low-complexity RA designs achieve comparable performance with reduced rotation complexity.