Study of wideband patch-based Butler matrix and its high-frequency application

In this paper, a wideband Butler matrix based on the 3-dB cross-slotted patch hybrid couplers and interdigital coupled-line section is presented. After loading a tight-coupled-line section at each port of the coupler, the operating bandwidth is enhanced with one more transmission pole. The Butler matrix is first designed and implemented at 2.65 GHz, with about 36% -10dB return loss bandwidth. Amplitude imbalance of ±1dB achieves about 38% bandwidth, while the 45°±2° phase difference bandwidth is around 29.6%. In addition, its Ku-band version operating at 12.5 GHz is also designed and well investigated.