Design of Wideband Circularly Polarized Filtering Antenna with High Frequency Selectivity and Gain Flatness

—In the paper, a wideband circularly polarized (CP) filtering antenna is proposed, which is composed of four bent Vivaldi elements excited with sequential-rotated feeding technique. Since the Vivaldi element has the advantages of high gain and wide bandwidth, it is selected as the radiation element. On this basis, two cross slots are etched on the Vivaldi antenna to increase the gain at lower frequency band, and bent method which has less effect on the overall performance is applied for lowing the profile of the antenna. To realize filtering characteristic, the quadrature four-feed network consisting of one modified miniaturized filtering rat race coupler (FRC) and two compact wideband quadrature couplers is utilized as the sequential-rotated feeding for the Vivaldi elements.