Huygens metasurfaces (HMSs) are 2-D structures exhibiting both electric and magnetic responses. In this article, the properties of a parallel-plate waveguide (PPW) formed by two dispersive reactive HMSs are investigated analytically by deriving the dispersion relations for supported surface waves. In particular, the PPWs formed by nondispersive HMSs are studied thoroughly and it is shown that they can support a maximum of four modes with a variety of transverse electric (TE) and transverse magnetic (TM) degenerate modes, modes with the same cutoff frequencies, and modes with constant phase and group velocities. Such explored PPWs offer degenerate modes with orthogonal polarizations with potential applications in leaky wave antennas and holographs. Moreover, PPWs with either nondispersive or dispersive borders support modes with subluminal phase velocities which find applications in device miniaturization. The proposed analytical derivations are verified by full-wave numerical simulations.
