A High-Gain Circularly Polarized Filtering Stacked Patch Antenna

Abstract

A high-gain circularly polarized (CP) filtering stacked patch antenna with independently controllable radiation nulls is designed without an additional filtering circuit/network in this letter. The lower radiation patch consists of a square outer loop and a three-quarter circular inner ring to realize CP radiation, with the inner ring connected to two adjacent edges of the outer loop. In addition, the upper stacked patch provides improved impedance matching and CP characteristics within the passband. Furthermore, a U-slot and square annular slot are etched on the lower and upper patch to generate two radiation nulls and obtain a filtering characteristic in the lower and upper stopband, respectively. A prototype is fabricated and measured, and the measured results show that the proposed antenna can provide an impedance bandwidth of 15.2% (1.83-2.13 GHz), an axial ratio bandwidth of 8.2% (1.87-2.03 GHz), and a gain higher than 7.0 dBi.