Design of Notched-Wideband Bandpass Filters With Reconfigurable Bandwidth Based on Terminated Cross-Shaped Resonators

In this paper, a series of novel reconfigurable-bandwidth notched-wideband bandpass filters (NWB BPFs) with controllable notch bands are proposed. The proposed filters start from a passive filtering structure, which is formed by a terminated cross-shaped resonator (TCSR) with a pair of parallel-coupled lines and two open-ended stubs. Theoretical analysis finds that the filter bandwidth can be independently controlled by the TCSR, while the center frequencies and bandwidth of notch bands are mainly controlled by the rest parts. According to this, a BPF with controllable notch bands can be designed. To achieve the reconfigurable-bandwidth NWB BPFs with controllable notch band, whose bandwidth and center frequency can be maintained unchanged under different work states, two PIN diodes and a varactor are employed. By controlling the work states of PIN diodes, three bandwidth states can be achieved with fixed center frequency. By controlling the applied voltage on the varactor, other NWB BPF with independently tunable lower passband edge can be realized. For verification, three prototypes are designed and measured. The measured results agree well with the theoretical analysis and simulated ones, verifying a simple and effective design approach of reconfigurable-bandwidth NWB BPFs.