Low Loss Tunable Superconducting Dual-Mode Filter at L-Band Using Semiconductor Varactors

This letter presents a superconducting continuously tunable bandpass filter with dual-mode resonator and Gallium arsenide (GaAs) varactors. The even- and odd-modes of the dual-mode resonator can be tuned simultaneously using a single bias voltage. The interstage and external couplings are realized with interdigital coupling structure to enhance the coupling strength. A four-pole dual-mode superconducting filter at L-band with a fractional bandwidth of approximately 20% is successfully designed. Two transmission zeros are generated in the upper stopband to increase the stopband rejection. The tuning range of the filter is 16% from 784.92 to 918.23 MHz. The insertion loss at 918.23 MHz is 0.69 dB with a reverse bias voltage of 9 V. The measurements of the filter match well with the simulated ones.