Center-fed Dual-band Circularly Polarized Microstrip Antennas

As Global Navigation Satellite Systems (GNSS) are developed towards multimode,multi-system, and high-precision operations, antennas for GNSS need to feature multi-band,circular polarization (CP), wide beamwidth, and low backside level. In this paper, dual-bandCP antennas with extremely low backside level and wide beamwidth are presented, includinga center-fed dual-band CP microstrip antenna, a center-fed antenna with three choke rings anda center-fed antenna based on reactive impedance surface (RIS). The main contributions ofthis work include:1. A novel and simple center-fed dual-band CP microstrip antenna is developed. Theantenna consists of a center-fed probe, an open squared ring slot, two stacked patcheswith stubs and a folded ground plane. The centrally located feed probe can minimize theinfluence on the radiation performance of the patch，enabling low cross polarization. Theopen squared ring slot can change the radial current distribution on the patches, makingbroadside radiation possible. Two stacked patches with stubs realize dual-band CPoperation. The folded ground plane improves low elevation gain and reduces crosspolarization level. Experimental results show that the antenna achieves two operatingbands, circular polarization and wide beamwidth. The antenna has a cross polarizationlevel of-15dB over the whole upper half space.2. A center-fed antenna based on choke rings is investigated. The antenna is composed of acenter-fed dual-band circularly polarized antenna and three choke rings. Three chokerings can block surface wave propagation and thus reduce the backside radiation.Experimental results show that the dual-band antenna can achieve extremely lowbackside level and a wide beamwidth (3-dB axial ratio beamwidth of the antenna coversthe whole half space). The antenna has a front-to-back ratio (FBR) above25dB. Thisantenna has potential applications for high precision ship GNSS.3. A center-fed antenna based on RIS is designed. This antenna includes a55RIS arrayand a center-fed dual-band circularly polarized antenna. The RIS array can improve theFBR, increase the frequency bandwidth and lower the antenna profile. Experimentalresults indicate that the dual-band antenna achieves extremely low backside level and wide beamwidth. The antenna has a3-dB axial ratio beamwidth of more than180and aFBR above24dB, suitable for high precision ship GNSS applications.