Resonator Reuse Approach for Implementing Narrowband Bandpass–Bandstop Cascade Based on Mode Orthogonality

This brief is to present a resonator reuse approach in implementing a high-attenuation notch next to a passband. Each resonator is utilized twice in producing bandpass and bandstop responses at the same time, which leads to size reduction. The filter structure employs cylindrical cavity resonators and utilizes the two orthogonal TM110 modes in each cavity resonator. The proposed filter has an excellent insertion loss since the TM110 mode has a high unloaded Q-factor. For verifying the proposed filter structure, we have designed and fabricated a second-order waveguide filter having a second-order bandpass-bandstop filter cascade response.