Design of a Broadband High-Gain Omnidirectional Antenna With Low Cross Polarization Based on Characteristic Mode Theory

A low-profile, high-gain, and low cross-polarization omnidirectional antenna is proposed. The antenna structure is pretty concise with convenient probe feeding and sandwich-structure design. The characteristic mode analysis shows that the antenna can excite quasi-TM01 and quasi-TM02 modes in a broadband and, thus, results in monopole radiation mode and low cross polarization in a broad operating band. The full-wave simulation and experiments were performed to verify the antenna design. The fabricated prototype antenna showed <2 dB unroundness and <−25 dB cross polarization in (4.8–11.1) GHz, with a relative bandwidth of 79.2% and a peak gain of 8.4 dBi at 9 GHz.