Compact Dual-Mode CP Antenna With Wide AR Beamwidths for BDS-Based Vehicular Applications

Reliable vehicular tracking of BeiDou Navigation Satellite System (BDS) satellites requires compact antennas offering circular polarization (CP), dual-band operation, and wide-angle axial-ratio (AR) performance. This paper presents a low-profile single-feed CP antenna that realizes dual-band CP through a frequency-driven dual-mode mechanism with structural reuse. The antenna comprises a microstrip feed, a shared cross-slot aperture, an air gap, and a suspended radiating patch. At 1176.45 MHz, the cross-slot operates as a pair of orthogonal magnetic-dipole radiators to generate right-hand circular polarization (RHCP). At 1575.42 MHz, the same cross-slot transitions to a coupling aperture that excites the suspended patch, forming a CP patch-dominant mode. This shared-aperture modal reconfiguration integrates two distinct CP mechanisms within a compact structure. Measurements show -10dB impedance bandwidths of 3.6% (1158–1200 MHz) and 3.8% (1538–1597 MHz). The 3-dB AR beamwidths reach 190° and 223° at the two bands, respectively, with measured RHCP gains of 3.5 and 6.5 dBic. The proposed antenna is suitable for compact BDS-based vehicular terminals requiring wide-angle satellite visibility.