Analysis and Design of a 45° Slant-Polarized Omnidirectional Antenna

A 45 degrees slant-polarized omnidirectional antenna is proposed for mobile communication base stations. The proposed antenna consists of four printed crossed-dipole elements which are rolled up into a cylinder for omnidirectional radiation. Each crossed-dipole element is composed of a horizontal dipole and a vertical dipole. The 45 degrees slant polarization is achieved by adjusting the lengths of the horizontal and vertical dipoles. A broadband feeding network consisting of four broadband baluns and an impedance matching circuit is introduced to feed the four crossed-dipole elements. Experimental results show that the omnidirectionality or gain variation in the horizontal plane is less than 1 dB while the cross-polarization level is below -15 dB over a bandwidth of 15% (1.9-2.2 GHz). The 45 degrees slant-polarized omnidirectional antenna has a bandwidth of 22% (1.75-2.18 GHz) for 15-dB return loss. Theoretical analysis and design procedure are presented.