A compact high-temperature superconducting band-pass filter with wide upper stopband

A novel hair-pin resonator(NHR) composed of interdigital capacitor and fractal resonator is developed, which not only has compact in size but also has no harmonics up to three times of the fundamental frequency. The results show that the equivalent capacitance introduced by the interdigital capacitor at the conventional hair-pin resonator terminal plays a major role in suppressing the spurious harmonics, whereas the equivalent inductance has no improved harmonic rejection ability. A miniature five-pole wide-band HTS bandpass microstrip filter has been designed and fabricated with this NHR on a double-sided MgO-based DBCO thin film. Measurement at 79.4K shows that the fabricated HTS filter has less than 0.11 dB insertion loss and better than 20 dB return loss in the passband, and an ultra high spurious passband at about 3.3f0. Moreover, the simulated and measured results are found in excellent agreement in wideband response.