An HTS wideband microstrip bandpass filter for L band receivers in radio astronomy observatory

This paper presents a high temperature superconducting (HTS) wideband microstrip bandpass filter with a novel microstrip configuration. Without additional defected ground aperture, the technique is applied in order to produce an 8-pole HTS filter at L band with a bandwidth of 26.2%. Quarter-wavelength resonators and internal coupling between resonators are realized by both interdigital capacitors (IDC) and capacitive open-ended stubs. Impedance steps and capacitive stubs are utilized for external couplings. The filter has less than 0.25dB insertion loss (including 0.2dB passband ripple), better than 14dB return loss and extremely steep transition region from passband to stopband at 77K. The measurement performance agrees well with the simulation.