Integrated multibeam dual-polarised planar array

Abstract

A novel four-beam dual-polarised microstrip antenna array at the 10GHz band is presented. By using a multilayered structure and multiport slot-coupled microstrip lines, two Butler matrix microstrip circuits corresponding to two orthogonal polarisations can be located on different substrate layers (above and below the ground plane) and integrated with a patch array. The antenna has eight input ports corresponding to two orthogonal polarisations and four beams. The theoretical design is based on the finite-difference time-domain (FDTD) method. The measured return loss and isolation characteristics exceed 10 and 23dB, respectively, in the 9.7-10.3GHz band. The radiation pattern is close to an ideal Butler pattern and the cross-polarisation level is lower than -18dB in the beams. Details of the antenna and its characteristics are presented.