A Compact Circularly Polarized Annular Ring Antenna with Wide Effective Bandwidth

This paper presents a simple excitation scheme for an annular ring circularly polarized patch antenna. The design provides overall miniaturization of the antenna without compromising the axial ratio, impedance matching and gain variation bandwidths. A branch line coupler is used to obtain phase quadrature between two signals which is then directly connected to the radiating patch by two metal posts. A prototype antenna is designed. Overall size of the antenna is $88 \mathbf{mm} \times 88\ \mathbf{mm} \times 10.5\ \mathbf{mm}$ with a measured peak gain of 4.9 dBi. Over the band, input matching is below −10 dB. An effective bandwidth is defined considering maximum 3 dB axial ratio, 10 dB return loss, and 3 dB gain variation. The proposed annular-ring patch antenna exhibits an effective bandwidth of 25.24% over 2.25-2.9 GHz. The antenna does not use any slot or other perturbation in the ground plane providing a scope for easy system integration.