Ultrathin Independently Controllable Multiband Reflective Polarization Rotator

Inspired by frequency-selective surface (FSS) design, this article presents a novel and simple design methodology for multiband reflective polarization rotators (RPRs), enabling independently controllable operating bands, and a compact unit cell. The main concept involves manipulating the current distribution of a loop resonator to convert linearly polarized incident waves into cross-polarized waves upon reflection. The RPR consists of three metal layers separated by two dielectric substrates, featuring a square loop on the top layer and a folded strip line in the middle layer connected by vias. Multi-band operation can be achieved by adding extra loops to the top layer, with each loop controlling its own frequency band. As a proof of concept, a dual-band RPR was designed using two square loops on the top layer operating in the [2.02–2.26] GHz and [4.12–4.48] GHz ranges. The design was extended to a tri-band by adding a third loop, operating at [1.54–1.7], [3.35–3.7], and [5.1–5.45] GHz. Thorough discussions of current distribution analysis, and experimental demonstrations are provided. The simulated results are validated through prototype measurements, showing good agreement with experimental data.