Bandpass Filter and Diplexer Based on Short-Circuited Stub-Embedded Resonators and Novel Coupling Scheme

A novel coupling scheme is proposed based on short-circuited stub-embedded resonator (SCSER) for bandpass filters (BPFs). The BPF utilizing SCSER owns three transmission zeros (TZs) that are controlled by short-circuited and open-circuited stubs. Based on the proposed SCSER and coupling structure, a novel high-isolation diplexer is presented. When the TZ is allocated in the opposite channel and impedance transformation is carried out in the common port, the proposed diplexer can be realized by directly combining two different BPFs without an additional matching network. For the demonstration, a BPF and a diplexer based on SCSER are fabricated and measured. The measured results agree well with the simulated ones.