Compact Ultrawideband Circularly Polarized Crossed-Dipole Antenna With Post Fence and Parasitic Elements

A compact ultrawideband circularly polarized crossed-dipole antenna with post fence and parasitic elements is proposed in this letter. The proposed antenna consists of two dipoles with unequal semiellipses, four symmetrical rectangular patches, and a post fence structure. Two vacant-quarter rings are utilized to provide the 90 degrees phase difference for feeding the cross-arranged dipoles. Wide axial ratio bandwidth (ARBW) is achieved by employing a metal pillar-back cavity through the introduction of five cavity modes, while also compacting the overall antenna structure. Four sequential rotating patches are positioned along the substrate edges to improve the axial ratio at higher frequencies. The proposed antenna exhibits an impedance bandwidth (IBW) from 0.87 GHz to 3.17 GHz and an ARBW from 0.98 GHz to 2.99 GHz. This indicates that the overlapped IBW and ARBW reach 101.3%. Moreover, the overall dimensions of the proposed antenna are 0.52 x 0.83 x 0.17 lambda(3)(L) corresponding to the lowest operating frequency, showing that it has great potential in wireless communications.