Complete Open-Stopband Suppression using Sinusoidally Modulated Anisotropic Metasurfaces

A novel and general approach is presented for the complete suppression of the open-stopband effects in circularly polarized one-dimensional periodic leaky-wave antennas using anisotropic modulated metasurfaces. A theoretical justification of this behaviour 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 behaviour. A closed-form formula for the leakage constant α is also derived, allowing for an accurate design of the aperture field amplitude. The full wave analysis of a patch-based implementation of the metasurface 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 open-stopband behaviour allows for the design of leaky-wave antennas able to scan the beam from backward to forward without any frequency regions of blindness