Miniaturized All stop to CABW tunable bandpass switchable filter using U-shaped multi-mode resonator

A pin diode loaded multi-mode resonator (MMR) based tunable filter has been presented in this manuscript. The filter consists of U-shaped resonator which are loaded with varactor tuned stubs at the middle. Also the resonator is loaded with PIN-diodes at the end. The proposed filter has two modes of operation based on the condition of PIN diodes - BPF mode, when the PIN diodes are ON and switch-off mode when the PIN diodes are OFF. In BPF mode, the proposed tunable filter maintains a constant bandwidth of the passband while tuning across different frequencies. A constant absolute bandwidth tunability has been achieved by controlling the first three modes - the odd mode and two even modes. The varactors have been introduced between the resonator and feed-line to maintain constant bandwidth while tuning. Additionally, the bandwidth reconfigurability at a fixed centre frequency can be achieved in the BPF mode of the proposed filter. In switch-off mode the filter will not allow to pass that particular band of frequencies. To demonstrate the concept, a filter has been designed and simulated to achieve a frequency tuning of 1.1 GHz to 1.8 GHz.