Evanescent waveguide-based polarisation-agile antenna elements

Polarisation-agile, evanescent waveguide-based antenna elements are proposed, which allow below waveguide cutoff operation from 1.07 to 1.49 GHz or below and above waveguide cutoff operation from 1.54 to 1.89 GHz for return loss 10 dB. Here square evanescent waveguide with 1.7 GHz cutoff is shunt loaded, respectively, with orthogonal pairs of coaxially excited cylindrical metal posts or flat metal strips positioned across the aperture of the waveguide. It is shown that linear or circular polarisation may be achieved depending on the excitations supplied to the input ports of the antenna.