Axial ratio beamwidth enhancement of a low-profile circularly polarized antenna using defected ground structures

This article explores the possibilities of incorporating a defected ground structure (DGS) for widening the 3 dB axial ratio beamwidth (ARBW) of a simple low-profile planar circularly polarized (CP) antenna. Two pairs of DGSs are etched symmetrically along the diagonals of the ground plane to overcome the limited 3 dB ARBW performance of a crossed-slotted circular-shaped planar CP antenna. Here, one pair of DGSs is orthogonal to another pair of DGSs. The distance between the pairs of DGSs plays a key role in enhancing the 3 dB ARBW by 40.62%. A gap of 0.18 lambda(0) is considered between the DGSs to maintain the symmetrical electric field distribution in the substrate. It also helps to reduce orthogonal current components and provides uniformly distributed patch surface currents. These phenomena collectively help the proposed CP antenna to exhibit right-handed circular polarization radiation with the 3 dB ARBW of 186 degrees and 188 degrees in the E-plane and H-plane, respectively. The measured results yield impedance bandwidth (S-11 <= -10 dB) of 2.6% (2.283-2.342 GHz), CP bandwidth of 0.9% (2.294-2.315 GHz), gain higher than 4.8 dBic, and total antenna efficiency more than 64% across the entire CP band.