Complete Open-Stopband Suppression Using Sinusoidally Modulated Anisotropic Metasurfaces

A novel and general approach is presented for the complete suppression of the open-stopband (OSB) effects in circularly polarized 1-D periodic leaky-wave antennas (LWAs) using anisotropic modulated metasurfaces (MTSs). A theoretical justification of this behavior is found through the rigorous treatment of the canonical problem of an infinite homogenized impedance surface sinusoidally modulated along the propagation direction. By deriving a closed-form solution of this problem at broadside scan, it is shown that, while the sinusoidally modulated isotropic impedance exhibits a null of the attenuation constant, the complex propagation constant for the proposed anisotropic modulation has a finite value and a regular behavior. A closed form formula for the leakage constant alpha is also derived, allowing for an accurate design of the aperture field amplitude. The full-wave analysis of a patch-based implementation of the MTS is in excellent agreement with the results based on the homogenized impedance model, thus demonstrating the practical applicability of the theoretical results. The elimination of the OSB behavior allows for the design of LWAs able to scan the beam from backward (BWD) to forward (FWD) without any frequency regions of blindness.