A tunable high temperature superconducting bandpass filter using semiconductor varactors

Abstract

A narrow band 4-pole varactor tuned high temperature superconducting (HTS) filter was design and fabricated. The center frequency of the filter can be tuned from 430 MHz to 720 MHz with a direct voltage up to 20V. The return loss is better than 10 dB in the whole tuning range. Insertion loss is in a range of 0.8~3.8 dB with 3dB fractional bandwidth about 3%.