A compact HTS bandpass microstrip filter with novel coupling structure for on-chip integration

• A novel coupling scheme is used to introduce two transmission zeros using only three resonators.
• The filter has a low insertion loss at 40 K, and a wide stopband with good rejection.
• The filter has compactness and high-selectivity.
• The filter is a suitable candidate for on-chip integration of HTS receiver front-ends.

A compact low-complexity high-selectivity high-temperature superconducting (HTS) microstrip bandpass filter is presented in this paper, which consists of only three half-wavelength resonators. A novel coupling scheme is used to provide a pair of transmission zeros outside the passband, so that the selectivity of the filter is improved. The filter is fabricated on an MgO substrate with YBa2Cu3O7−x (YBCO) coating. Measurement result shows an in-band insertion loss at 0.5 dB, a sharp slope, and a stopband rejection better than 20 dB. The compactness and high-selectivity features make the filter suitable for on-chip integration of HTS receiver front-ends.