Metasurface waveguides applied to matched feeds for reflector antennas

Waveguides with anisotropic surface impedance boundaries have been investigated for the purpose of matched feeds for offset reflectors. Matched feeds employ higher order waveguide modes to cancel out cross polarization introduced by the offset geometry. Since the higher order modes propagate at different speeds than the fundamental mode in conventional waveguides, it is challenging to meet phase relationship requirements over a large band. We have found that traditional corrugated waveguides are poorly suited for matched feed applications. However, other surfaces that satisfy the balanced hybrid condition, but have a small capacitive longitudinal reactance and large inductive azimuthal reactance show very promising properties: In a large band, HE11 and HE21 have similar propagation characteristics.