Shichao Jin

Design of a High-Power Superconducting Filter Using Resonators With Different Linewidths

This paper presents a design method to develop a high-power superconducting microstrip filter with different linewidth resonators. The linewidth of every resonator is optimized using this method to meet the same maximum current density. Thus, the power-handling capability of the five-pole filter on a limited substrate size can reach a maximum value. The design method is verified by the electromagnetic simulation of the current density distribution. The high-power superconducting filter is designed and fabricated on a 38 mm times 30 mm times 0.505 mm LaAlO3 substrate. The maximum resonator linewidth is 7 mm, and the minimum one is 1.6 mm. The filter has a center frequency of 2006 MHz and a narrow bandwidth of 1.0%. The measured power level is up to 35 dBm at 65 K without an evident change in insertion loss.

Design and Performance of an Ultra-Narrowband Superconducting Filter at UHF Band

A stepped impedance spiral resonator suitable for high-temperature superconducting (HTS) filter with bandwidth narrower than 0.5% is presented. An eight-pole demonstration HTS filter is developed with a central frequency of 650 MHz and a bandwidth of 0.3%. The measurements show that the insertion loss is less than 0.3 dB, and the return loss is better than 16 dB. The filter has out-of-band rejections of 65 dB at 2 MHz below the passband and 80 dB at 2 MHz above the passband, respectively.

UHF Band Ultra-Narrowband Superconducting Filter With Double U-Type Secondary Coupling Structure

A double U-type secondary coupling structure (DUSCS) is used for a compact ultra-narrowband filter in the ultra-high frequency (UHF) band. It can effectively reduce the coupling and thus spacing between coupled twin-spiral resonators. A six-pole superconducting filter at 600 MHz with a fractional bandwidth of 0.083% is designed and fabricated to validate this technique. The filter size is reduced by 15% compared with the filter designed without DUSCSs.

Center Frequency Tuning for a Narrowband Superconducting Filter in the Time Domain

This paper presents a mechanical tuning method for tuning the center frequency of a narrowband high-temperature superconducting filter. The filter is designed with 0.5-MHz bandwidth at 166.9 MHz and is fabricated. Tuning is carried out based on the time-domain response of filter return loss. The filter can be precisely tuned to a desired center frequency while maintaining a high-frequency performance. The center frequency is tuned from 167.2 to 166.5 MHz. The tuning range is 0.7 MHz and is sufficient to compensate the frequency offset caused by 0.72% variation in the substrate effective dielectric constant or 4% that of the substrate thickness.

An HTS Wideband Filter Using Interdigital-Like Resonators at UHF Band

A wideband superconducting interdigital-like filter at UHF band has been successfully designed and fabricated. An interdigital-like resonator is proposed to realize both strong coupling and compact size. A ten-pole demonstration high temperature superconducting filter is developed with a center frequency of approximately 340 MHz and a fractional bandwidth of 26%. The measurements show that the insertion loss of the filter is less than 0.2 dB, the return loss is better than 17 dB, and the out-of-band rejection is better than 70 dB.

An Ultra-Narrowband Miniature Superconducting Microstrip Filter at VHF Band

This paper presents a four-pole superconducting filter with an ultra-narrow bandwidth of only 440 kHz at 220 MHz. A pair of symmetrical transmission zeros is introduced to improve the steepness of the bandedges. The filter circuit is realized on YBCO/MgO with an area of 36.6 mm×12.4 mm. The measured results show a high performance and are in good agreement with the simulations. The minimum insertion loss is 0.42 dB, the return loss is better than 15 dB, and the out-of-band rejection is better than 60 dB.