Low-Profile Ultra-Wideband Dual-Polarized Omnidirectional Antenna for Indoor Base Station

A low-profile ultra-wideband omnidirectional antenna with dual polarizations for indoor mobile communication is presented. The horizontally polarized (HP) omnidirectional element is introduced by using 12 I-shaped slot antennas, which are arranged in a circle-shaped array and excited by a 1-to-12 power divider. The vertically polarized (VP) omnidirectional performance is introduced by using a dual-M-shaped monopole with a small ground plane. To enhance the impedance matching within an ultra-wide bandwidth, a top metal disk with four chunks, a bottom metal loop, and a ring slot embedded in the ground plane are employed for the design of the VP element. After replacing the metal disk of the VP element with the designed HP element, the omnidirectional antenna with dual polarizations is then simply achieved. By utilizing this new method, an ultra-wideband dual-polarized omnidirectional antenna for indoor mobile communications is designed, manufactured, and measured. It has an ultra-wide bandwidth of 117% (1.44–5.5 GHz), high isolation of 30 dB, and a low profile of $0.16\lambda _{\mathrm {L}}$ ( $\lambda _{\mathrm {L}}$ denotes the wavelength at the lowest frequency of the operating band). Good omnidirectional radiation performance with gain variation < 2.6 dBi is obtained for both HP and VP ports over the ultra-wide operating band.