Design of Novel Reconfigurable Filter With Simultaneously Tunable and Switchable Passband

This paper presents a new loading scheme for adding the varactor and PIN diodes into a quarter-wavelength (λ/4) resonator. Based on this, a novel reconfigurable filter with simultaneously tunable and switchable passband is introduced. Constant absolute bandwidth (ABW) and two transmission zeroes (TZs) can be obtained to enhance the passband performance in the ON-state. As the passband is turned to the OFF-state, high isolation can be realized at the frequency of interest. Meanwhile, the varactors, which are used to control the external quality factor (Qe) in the ON-state, can be tuned to improve the in-band isolation in the OFF-state. For demonstration, a reconfigurable filter with tunable and switchable passband is fabricated and measured. The measured results show a high selectivity tunable passband with the tuning range of 32.4% and 3-dB ABW of 51 ± 2 MHz in the ON-state. The isolation >40dB can be achieved in the OFF-state. Good agreement of the simulated and measured results is presented to verify the theoretical predictions.