Design of a Low Profile Omnidirectional Circular Polarized Reconfigurable Antenna for Beidou Application

A low profile omnidirectional circular polarized reconfigurable antenna for Beidou application is proposed in this paper. This antenna is based on the first-order resonance mode of epsilon negative transmission line. To form a circularly polarized wave in the far field, the vertical and horizontal polarization is generated by a parallel circular cavity and three dual arc arms, respectively. Only 6 PIN diodes are needed to alter the left-handed circularly polarized (LHCP) or righthanded circularly polarized (RHCP) omnidirectional radiation state. Three-dimensional electromagnetic simulation software Ansoft HFSS and RF circuit simulation software Agilent ADS are used for co-simulation and optimization. It is shown that the proposed antenna can meet the Beidou navigation BDS-l S band requirement well whether at the left or right circularly polarized state. The omnidirectional average axial ratio at two states are 1.24 dB and 1.25 dB with 16.7 % and 19.8 % 3 dB axial ratio bandwidth, respectively. The thickness of antenna is only 2 mm (0.016 λ₀) and simply processed without a dual feeding structure and 90 phase shifter.