Vanadium-Dioxide-Based Reconfigurable Ka-Band Dual-Sense Linear-to-Circular Polarizer

We propose a reconfigurable dual-sense linear-to-circular polarization (LCP) converter in the form of a VO2-based metasurface. VO2 is a phase change material (PCM) that is useful for low-loss mmWave devices, being transparent in its insulating state and metallic when heated. The device operates in the satellite communications uplink portion of Ka-band (27.5–31 GHz). It consists of a four-layer meanderline metasurface with two overlapping configurations, rotated relatively by 90° in- plane, for right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) conversion. Each configuration is interrupted by VO2 patches with double spiral NiCr microheaters along the meandered traces. Under dc bias, the VO2 of one trace changes from insulator to conductor, activating the configuration. The simulated design exhibits axial ratio (AR) $\le0.99$ dB and insertion loss (IL) $\le2.59$ , for both RHCP and LHCP conversion. After verifying the dual-sense RF design in simulation, single-sense LCP conversion was measured. The measured results are for LHCP conversion with AR $\le2.1$ dB and IL $\le4.0$ dB. The LHCP conversion also has 1-dB AR from 30.2–32.4 GHz and 3-dB AR from 27–38 GHz (26% circular polarization bandwidth). This study demonstrates for the first time LCP conversion using a transmission-mode reconfigurable metasurface in Ka-band using VO2 PCM, and simple dc activation network.