HTS Filter with Dielectric Rods for Tuning the Center Frequency and Trimming the Passband ripple

Abstract

Tuneable filters are one of the most essential microwave components for multiband communication systems due to their attractive features. In this study, we developed high-temperature superconducting (HTS) tuneable microstrip line hair-pin resonator filter with dielectric rods for tuning the center frequency and trimming the passband ripple simultaneously. Several dielectric rods are placed above the HTS filter, and the center frequency and passband ripple are controlled by changing the distance between the dielectric rods and the resonators. Two dielectric rods are used for each resonator; one is located on the center of the resonator for tuning the center frequency and trimming the pass-band ripple, and the other is located on the open end of the resonator to tune the center frequency. The filter was designed to have a center frequency of 1.4 GHz and a bandwidth of 28 MHz by using an electromagnetic simulator based on the moment method. The HTS filter was fabricated using double-sided YBa2Cu3Oy thin film on a 30×40×0.5 mm Al2O3 substrate. The dielectric rods with a dielectric constant of 39 were used. As a result, the tuning range of the filter was about 140 MHz while keeping the all most the same insertion loss with trimming. The measurement data after trimming and tuning have a good agreement with the design specifications.