Integrated multibeam dual-polarised planar array

A novel four-beam dual-polarised microstrip antenna array at the 10 GHz 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 23 dB, respectively, in the 9.7–10.3 GHz band. The radiation pattern is close to an ideal Butler pattern and the cross-polarisation level is lower than –18 dB in the beams. Details of the antenna and its characteristics are presented.