Low-Temperature Superconducting RF Integrated Filters for Multi-Band Cryogenic Applications

This work discusses on-chip integrated low-temperature superconducting (LTS) filters that possess triple passbands with prescribed equiripple performance. Based on a polynomial synthesis approach, equal ripple response can be achieved in each passband by introducing a pair of additional transmission zeros (TZ). In addition, two different ripple factors are set for three symmetrical passbands, and their ratios can make the return loss (RL) levels different and controllable. The prototype, after proper transformation /simplification, is then corresponded to lumped inductors and capacitors on-chip using a 4-metal layer LTS Niobium process. With an enhancement of out-band attenuation (thanks to the finite TZs), the filter is expected to be implemented with superconducting rapid single- flux-quantum (RSFQ) logics for generating narrow-line-width microwave pulses for different cryogenic applications.