Design and discussion of a broadband cross-dipole with high isolation and low cross-polarisation utilising strong mutual coupling

A broadband cross-dipole with high isolation and low cross-polarisation for base station applications in mobile wireless communications is presented in this study. By skillfully utilising the strong mutual coupling between the two dipoles, very good impedance match, sufficiently high isolation and low cross-polarisation can be achieved simultaneously. The measured results show that a more than 54% impedance bandwidth for standing wave ratio (SWR) < 1.5 from 1.695 to 2.95 GHz is achieved, within which the isolation is larger than 35 dB and the cross-polarisation is less than -34 dB. As a desirable advantage, the input impedance of the antenna can be changed within certain limits by properly adjusting the configuration, thus the antenna can be fed directly by 50-ω coaxial cables without the aid of impedance transformers. Particularly, besides the designing and the optimising work, the mechanisms for high isolation and low cross-polarisation as well as the method to adjust the input impedance are also discussed from a new point of view, which are also appropriate for other cross-dipole with the similar patterns.