A miniaturised butler matrix based on patch hybrid couplers with cross slots

Abstract

In this paper, a miniaturised Butler matrix using 3-dB cross-slotted patch hybrids is presented. By asymmetrically loading the inductive cross-slotted slots on four patches, compact patch hybrid couplers can be achieved. After properly installing two quarter-wavelength short-circuited stubs as phase shifters, the overall size of the resultant Butler matrix is largely reduced. In comparison with traditional patch hybrids with half-wavelength side-length, the side-length of proposed one can be shorter than quarter-wavelength. It means that the over all circuit area achieves an area reduction of about 56%, while the comparable performance is maintained, where the -10dB return loss bandwidth is more than 14%, +/-0.7 dB amplitude balance bandwidth is more than 10%, and the 45◦ +/-5◦ phase difference bandwidth is around 14%. Finally, a prototype of proposed Butler matrix is fabricated and verified experimentally.