Dual-band circularly polarized S-shaped slotted patch antenna with a small frequency-ratio

A dual-band single-feed circularly polarized, $S$-shaped slotted patch antenna with a small frequency-ratio is proposed for GPS applications. An $S$-shaped slot is cut at the centre of a square patch radiator for dual-band operation. A single microstrip feed-line is underneath the center of the coupling aperture ground-plane. The frequency-ratio of the antenna can be controlled by adjusting the $S$-shaped slot arm lengths. The measured 10-dB return loss bandwidths for the lower and upper-bands are 16% (1.1031.297 GHz) and 12.5% (1.4441.636 GHz), respectively. The measured 3-dB axial-ratio (AR) bandwidth is 6.9% (1.1951.128 GHz) for the lower-band and 0.6% (1.5681.577 GHz) for the upper-band. The measured gain is more than 5.0 dBic over both the bands. The measured frequency-ratio is 1.28. The overall antenna size is 0.46 $\lambda-{o}\times 0.46 \lambda-{o}\times 0.086 \lambda-{o}$ at 1.2 GHz.