Dual-band dual-sense circularly polarized annular ring slot antenna

This paper proposes a novel dual-band dual-sense circularly polarized (CP) annular ring slot antenna. The antenna consists of two concentric annular ring slots to achieve dual-band operation. The dual-sense circular polarization can be obtained by loading proper lumped capacitors across the inner and outer slots at +45° and -45°, respectively, with respect to the microstrip feed line. An antenna prototype was implemented and measured to validate the design concept, showing that the antenna achieves good left-hand circular polarization (LHCP) for the lower band and right-hand circular polarization (RHCP) for the upper band. The measured 10-dB impedance bandwidths are about 21.5% and 22.5%, respectively, for the lower and upper bands. The measured 3-dB axial ratio (AR) bandwidths are nearly 3.7% and 5.8% for the lower and upper bands, respectively.