Solving Sub-Wavelength Lattice Reduction in Full-Metal Front-Ends for Dual-Polarized Active Antennas

This article proposes an original structure of evanescent quadridge antenna (EQA) to conceive dual-polarized full-metal front-ends that can be used in active antennas (AAs) with wide field-of-view (FoV). An original design methodology is here proposed that allows to induce radiation from subwavelength squared apertures based on the use of evanescent and quadridge waveguides. The proposal is illustrated by means of a design with 4.5% bandwidth providing dual-circular polarization (CP) with good performance up to 50°-scanning even in the diagonal plane. For comparison purposes, a metallic benchmark is also proposed, which is based on the use of classical quadridge horns. Such comparative analysis allows to understand the superior performance of the proposed concept and its main advantage: it allows to avoid the excitation of the first high order mode in the squared quadridge aperture. The excitation of such spurious mode in the antenna is explained in terms of simple equivalent circuit models characterizing the aperture periodic discontinuity.