An Ultra-Broadband, Low-Profile, Vertical-Polarized Omnidirectional Antenna Designed with the Assistance of Eigenmode Analysis

An ultra-broadband cavity antenna with vertical-polarized monopole-like radiation patterns is developed for indoor communication. In order to achieve a low profile and ultra-broad operating frequency band, a metal cavity with a broadband characteristic is firstly presented by using the eigenmode analysis method. Then, a 1-to-4 power divider and four metal probes are utilized to excite the cavity to obtain vertical-polarized omnidirectional performance. For attaining an extremely broad bandwidth, four fan-shaped slots and four shorting pins are added in turn, and finally each metal probe in the vertically polarized cavity antenna is replaced with two identical small feed pins. By adopting this innovative scheme, a low-profile, ultra-broadband, omnidirectional cavity antenna with vertical polarization is procurable. It has a very wide impedance bandwidth of 105% (1.67–5.37 GHz) and a very low profile of 0.045λ, where λ represents the wavelength corresponding to the lowest frequency at the working band. Furthermore, the presented antenna also exhibits excellent omnidirectional radiation performance, making it suitable for indoor micro base stations.