Wideband planar coupled patch antennas with enhanced radiation pattern stability

Abstract

This article tries to address the unstable radiation pattern issue of the planar-coupled patch antennas with two different methods. First, characteristic mode analysis (CMA) reveals that the coupled patch antennas generate three characteristic modes with distinctive radiation patterns. A slot-loading scheme is proposed to reshape the current distribution of the higher mode and reduce its sidelobe level significantly. Then a 13.4% bandwidth with consistent radiation patterns and high gain is achieved by exciting modes 1 and 3 while suppressing unwanted modes with an aperture-coupled feeding. Second, the radiation pattern stability of the coupled patch antennas is further improved by employing shorted parasitic patches. The presented antenna can be equivalent as the same magnetic current array model under the in-phase and out-of-phase modes, and thus the radiation patterns hardly get changed. Moreover, the non-radioative nature and high radiation quality factor of the higher mode improve the radiation performance in a new principle. It not only enhances the bandwidth up to 18.5% but also results in a sharp filtering edge of gain response.