Design and performance of an HTS wideband microstrip bandpass filter at X-band

This article presents a 10-pole high-temperature superconducting (HTS) wideband microstrip bandpass filter with a novel configuration and compact size.The filter at 10 GHz with a fractional bandwidth of 40% is designed and fabricated on a 32.6 mm x 6.7 mm x 0.5 mm MgO substrate with double-sided YBCO films. The internal couplings between quarter-wavelength resonators are realized by parallel-coupled microstrip line (PCML) structure and capacitive open-ended stubs. The strong external couplings required by wideband filter are realized by impedance steps and capacitive stubs. The measured results at 55 K, without any tuning, show a high performance. The insertion loss is less than 0.31 dB, the return loss is better than 14 dB, and the out-of-band rejection is higher than 70 dB. The overall measurements are in good agreement with the simulations. (c) 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:10271029, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27485