Compact Butler Matrix based on Patch Element for X band Applications

The existing designs of Butler matrices are all based on microstrip lines, which may cause performance degradation when the operation frequency increases. To solve this problem, this article presents the design and realization of Butler matrix based on patch element. In order to achieve wideband and simple structure features, the circuit utilizes couplers with arbitrary phase difference and a novel crossover instead of the standard ones. With the help of patch element's unique advantages, the proposed matrix exhibits a good performance which covers a high frequency band ranging from 9 GHz to 11 GHz. The measurements show accurate phase differences of 45 degrees +/- 5 degrees, and with an amplitude imbalance less than 1dB. The return losses are better than -10 dB over a relative bandwidth of 20%. Meanwhile, the structure occupies a small area compared to conventional Butler matrices owe to its simplicity in topology.