Experimental Verification of Below-Cutoff Propagation and Chirality in Metasurface-Lined Waveguides

This article presents an experimental verification of cutoff manipulation and chiral properties in circular metallic waveguides through the insertion of a concentric metasurface (MTS) liner. These liners are shown to be readily implemented using Jerusalem-cross patterns printed onto a flexible dielectric substrate. The insertion of this MTS liner introduces an HE11 mode whose dispersion may be engineered to allow propagation well below the natural cutoff frequency of the waveguide. By rotating the Jerusalem-cross unit cells relative to the axis of the waveguide, it is shown that the dispersions of the left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) HE11 modes can be separated, creating a chiral behavior that can be controlled by the rotation angle. Spiral antennas are designed to excite the LHCP and RHCP modes through an MTS-lined waveguide section. The resulting S-parameter response of the MTS-lined waveguide is investigated numerically and then verified experimentally, demonstrating that the MTS-lined waveguide supports below-cutoff propagation and different responses to LHCP and RHCP modes.