Development of Trimming Technique for Superconducting Tunable Filters

We developed trimming techniques for superconducting tunable filters with a dielectric tuning plate and dielectric trimming rods. We designed a 5-pole filter with 5-GHz center frequency and 100-MHz bandwidth using an electromagnetic field analysis simulator. We proposed the trimming techniques by using a trimming library. A trimming library refers to a collection of calculated data of frequency responses that is assembled in order to compare it with experimental data. We constructed the trimming library using a circuit analysis simulator (S-NAP). First, we designed a conventional π -type equivalent circuit with optimal band-pass filter (BPF) characteristics. We determined all C and L values to meet the specifications of the filter by using the S-NAP. Next, we calculated the filter characteristics by C values of each resonator. The changes in C were assumed to be 1%. The filter characteristics changed substantially with a 1% reduction in C. We were able to determine the most adjusting points for the trimming rods using the trimming library consisting of S11 properties. These results indicate that our method will be useful for the next generation of software-defined radio (SDR) systems.