Omnidirectional circularly polarized base station antenna with high gain and wide band

In this paper, an omnidirectional circularly polarized (OCP) antenna is designed for base stations, providing high gain and wide axial ratio (AR) bandwidth. The six-stage OCP antenna is built from cascaded spiral rings and vertical dipoles. To improve the roundness and enlarge the AR bandwidth, spirals in shunt are utilized in proximity to the feeding. Then, network characteristic mode theory is employed to provide frequency reconfiguration, to further expand AR bandwidth. Four internal ports are introduced at the current maximums of the OCP antenna. With proper reactive loads at the internal ports, the CP performances with omnidirectional patterns are reconstructed at a higher frequency band. As a result, the OCP antenna operates at the band of 3.3-3.78 GHz, with a maximum gain of 7.38 dBic. The out-of-roundness of pattern is less than 2.5 dB, indicating robust omnidirectional radiation performances.