A Narrowband Superconducting Quadruplexer With High Isolation

A manifold-coupled microstrip superconducting quadruplexer with high isolation for S-band communications systems is presented. The problems of channel isolation and common-port impedance matching in the design of the quadruplexer are addressed and studied. An equivalent circuit model for a trial diplexer is built to analyze the isolation between two channel filters with Chebyshev responses. Analyses and simulations show that channel isolation is mainly determined by the resonators that are closest to the noncommon ports. A circuit layout is proposed for the quadruplexer to obtain high isolation. Moreover, a binary matching network is designed to minimize the undesired interactions between the four channel filters in the quadruplexer. The quadruplexer is successfully designed with the proposed methods and fabricated. The measured results show high performance and match well with the simulations.