2-2.2 GHz Reconfigurable 1 × 4 Filtering Beamforming Network Using Novel Filtering Switch-Coupler and Twisted Rat-Race Coupler

In this article, a reconfigurable 1 × 4 filtering beamforming network using a novel filtering switch coupler and twisted broadband rat-race coupler is proposed. The filtering switch coupler is constructed by four evanescent-mode cavity (EVA) resonators that are connected by varactors. By controlling the capacitance value of varactors, switchable 0°, 90°, -90°, or 180° output phase differences at fixed output ports can be obtained. The broadband rat-race coupler is realized by integrating a crossover inside a conventional broadband rat-race coupler. With such a simple technique, the center area of the conventional broadband coupler is fully utilized, resulting in a size reduction; more importantly, the output ports are adjusted to be adjacent to each other, resulting in a convenient position for next-stage connection. By using the proposed filtering switching coupler and twisted broad-band rat-race coupler, a 1 × 4 beamforming network is demonstrated. It exhibits more integrated functionalities, including filtering response and reconfigurable center frequencies with a similar amount of circuit components as the conventional Butler matrix network, providing an alternative solution to conventional beamforming networks in recognition radios. Detailed simulation and measurement have been given to demonstrate the techniques.