Design of a Sixth-Order Switchable Superconducting Balanced Filter Using Asymmetric Coupled SIRs

A stopband-extended sixth-order balanced bandpass filter with switchable passband function and stopband response is proposed in this paper. Based on the use of asymmetric coupled stepped-impedance resonators, the upper differential-mode stopband can be extended, and high common-mode suppression can be performed within passband. By means of high-order structure and cross coupling, which introduce transmission zeros closely around the passband, high selectivity is attained. The configuration utilizing switchable cross coupling is eventually employed in the balanced filter to perform either Elliptic function with steep passband edge or Chebyshev function with flat and deep stopband. The circuit is fabricated in high-temperature superconducting technique on an MgO substrate with YBCO thin films, which can result in relatively low insertion losses. Experiment at the temperature of 77 K was carried out to validate the design concept. The results attain good agreement with the predicted ones in simulation.