A Wideband Filtering Switch: Its Synthesis and Design

This article presents a direct synthesis method for the design of a wideband filtering switch, where p-i-n diodes are incorporated into each resonator. As parasitic parameters are embedded in the p-i-n diodes, an ideal transformer is introduced in each resonator to provide the freedom to designate the proper values for inductances and capacitances in the resonators. According to the rejection specification in the on state, an N th order bandpass filter (BPF) network with N transmission zeros (TZs) is synthesized, followed by a new circuit model extraction procedure to extract lumped circuits in the BPF network. To simplify the network topology, two ideal transformers at input–output port remain after absorbing the ideal transformers between resonators. Then, the lumped circuit model is converted into a distributed circuit model in the synthesis process, maintaining the filtering response in a wide frequency range when the switch is in the on state. Besides, the N TZs of the filtering switch in the off state can be introduced and arranged to suitable positions. Consequently, high isolation within the stopband of the switch in the off state can be achieved. For demonstration purposes, two filtering switches with fractional bandwidths (FBWs) of 30% and 50% are fabricated and measured. Good agreement can be observed between the simulated and measured results, which validates the feasibility of the proposed method.