Wideband asymmetric microstrip-fed circularly polarized antenna with monofilar spiral stub for WLAN application

A wideband circularly polarized printed antenna is proposed and fabricated, which employs monofilar spiral stubs and a slit in the asymmetrical ground plane which are fed by an inverted L-shaped microstrip feedline. The CP operation is realized by embedding an inverted-L shaped strip and modified ground plane and can be markedly improved by loading monofilar spiral stubs asymmetrically connected at the edge of the ground plane. After optimization, the measured results of the finally structure demonstrate that a 10-dB bandwidth of 67.6% from 4.6 to 9.3 GHz and a 3-dB axial-ratio bandwidth (ARBW) for circular polarization (CP) of 60.1% from 5 to 9.3 GHz could be achieved which could completely cover the WLAN (5.725-5.85 GHz) band. Therefore, the proposed antenna is suitable for circular polarization applications in C band. To explain the mechanism of broadband circular polarization operation, the analysis of magnetic fields distributions and a parametric study of the design are given. Compared to other recent works, a simpler structure, wider axial ratio and impedance bandwidths and a more compact size are the key features of the proposed antenna.