A Compact Circularly Polarized Filtering Dipole Antenna With Co-Layered Printed Ring Structures

This letter presents a simple structure wideband circularly polarized (CP) dipole antenna with bandpass-type filtering radiation response. It consists of a cross-dipole radiator with the arms printed on both the top and bottom sides of the substrate. Four pairs of rotated metal strips and a compact square ring structure are coupled to the arms to enhance the axial ratio (AR) bandwidth. In order to realize bandpass-type filtering radiation response, two rectangular rings are introduced to generate two specific radiation nulls, ensuring high-frequency selectivity at operating band edges. To obtain compact size and avoid intersection with the dipole arms, the two ring structures are printed on the top and bottom sides of the substrate using the metallic jumper vias. This wideband CP filtering dipole antenna is implemented and tested. The antenna oversize is 0.8 lambda(0) x 0.8 lambda(0) x 0.17 lambda(0). The measured results show that the proposed antenna has an overlap impedance and AR bandwidth of 14.1%. A stable realized gain of about 7.2 dBic and two radiation nulls are obtained without using extra filter circuits.