Series-Fed Dual-Polarized Single-Layer Linear Patch Array with High Polarization Purity

In this letter, a novel dual-polarized 1 × 4 patch array using proximity feed technique is presented. The proposed single-layer antenna consists of four square patch elements, two short-terminated parallel coupled microstrip lines, and a rat-race incorporated in the feed network. The patches are placed at the inner space between the two parallel microstrip feedlines. Horizontal and vertical polarizations of the patch array are excited by the even and odd modes of the two microstrip lines, respectively. The rat-race structure is used to provide in-phase and 180° out-of-phase feeds for the two modes. A prototype operating at 3.5 GHz is fabricated and measured. The measured overlapping bandwidth of the two ports is 81 MHz, also with port isolation higher than 40 dB. Owing to the symmetry of the structure and balanced excitations, the measured cross polarizations are all below-29 dB in E-and H-planes.