A tunable bandpass-to-bandstop filter with controllable bandwidth and high rejection level

A tunable bandpass-to-bandstop filter with controllable bandwidth is proposed in this article. The bandpass-to-bandstop transformation can be achieved by adjusting the PIN diode, and bandwidth of the bandpass filter can be controlled by adjusting the voltage of varactors, as the coupling coefficients and the external quality factors (Q(e)) can be tuned by changing the ratios of the loaded capacitances. In the bandpass mode, a tuning range of 805-1032 MHz (24.7%) with return loss better than 11.5 dB can be achieved. In the bandstop mode, a tuning range of 760-1228 MHz (47.1%) can be obtained. The rejection level of the bandstop mode is higher than 40 dB. (c) 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:110-113, 2017