A compact high-Tc superconducting quarter-wavelength SIR bandpass filter

A compact high-temperature superconducting bandpass filter for wireless communications is proposed in this paper. The filter consists of four quarter-wavelength short-circuited stepped impedance resonators (SIR). A pair of transmission zeros outside the passband are introduced into the design by evaluating coupling coefficients between the four resonators for high selectivity within the frequency band of interest. The use of short-circuited quarter-wavelength SIRs has resulted in a higher spurious passband than conventional half-wavelength coupled-line filters. Based on the theoretical calculations, the filter has a compact size and exhibits a well suppressed stopband. The filter is fabricated on an MgO substrate with YBCO superconductor coating. Simulation and measurement results are presented.