Design of a wideband circularly polarised fractal-shaped slot antenna

Abstract

A wideband microstrip-line-fed fractal-shaped slot antenna is proposed for circular polarisation. An L-shaped stepped-impedance microstrip feed line coupled to two orthogonal boundaries of the slot is employed to generate circularly polarised (CP) radiation. The impedance and axial ratio (AR) bandwidths of the proposed antenna are improved at the same time with introducing fractal-shaped slots. Furthermore, parametric studies have been conducted to investigate the effect of several different geometrical parameters on the performance of the antenna. An antenna prototype has been implemented and measured to verify the design concept. Experimental results demonstrate that the proposed antenna has a measured 10-dB impedance bandwidth of 2.47 GHz (58.7%) from 2.97 to 5.44 GHz and a measured 3-dB AR bandwidth of 1.47 GHz (38.5%) from 3.08 to 4.55 GHz. The measured CP gain maintains above 3.0 dBic over the AR bandwidth with a maximum gain of 5.6 dBic. Details of design considerations and simulated and measured results are presented and discussed.