A Novel Dual-Feed Slot-Coupling Feeding Technique for Circularly Polarized Patch Arrays

In this letter, a novel slot-coupling feeding technique has been adopted to realize a circularly polarized (CP) 2 ?? 2 microstrip array. Each array element is fed through two microstrip lines that are excited 90?? out of phase (dual-feed technique) and coupled to a square patch by means of a square-ring slot realized in the feeding network ground plane. Design procedure, simulation results, and measurement data are presented for a 2 ?? 2 array working in the WiMax 3.3-3.8 GHz frequency band (14% percentage bandwidth). Due to both the symmetry properties of the novel slot-coupling feeding configuration and the implementation of a sequential rotation technique, excellent axial ratio (AR) performance is achieved in the WiMax band (AR < 1.35 dB at broadside) and for any direction in the antenna main beam (AR < 2.25 dB at 3.55 GHz). Actually, the 3-dB AR bandwidth is larger than the WiMax frequency band, as it goes up to about 30%.