A novel HTS filter with improved out‐of‐band rejection by introducing a quarter‐wavelength spiral stub

A novel high temperature superconducting (HTS) filter with split-end stepped impedance resonators (SIR) is developed on MgO substrate. Spiral feedlines are used to meet the requirement of the external quality factor. A quarter-wavelength (λ/4) spiral stub is introduced at the input feedline to provide additional transmission zeros at the high frequency end, which can improve both the out-of-band rejection and band-edge steepness. The measured results at 70 K are in good agreement with the simulated ones. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2455–2457, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23688