Design of Double Passband HTS Filter Based on SIR

Astepped-impedance-stubloadedstepped-imped ance resonator is proposed to design a dual-band bandpass filter in this paper. The center frequencies of the two passbands of this filter are 2818 MHz and 3715 MHz, respectively, with corresponding 1 dB passband widths of 2797 $\mathbf{M H z} \sim 2839 \mathrm{MHz}$ and $3687 \mathrm{MHz} \sim 3743 \mathrm{MHz}$. This filter is capable of generating four transmission zeros, which significantly enhance the out-of-band rejection capability of the filter. Specifically, the out-of-band rejection exceeds 60dB at the $3,802 \mathrm{MHz}$ and exceeds 70 dB at the 2651 MHz. In addition, the out-of-band suppression in the 2997MHz 3525MHz band is also up to more than 70 dB. Therefore, the filter has the advantages of good out-of-band suppression, compact structure and controllable frequency. The filter is designed by Sonnet, a full-wave electromagnetic simulation software. YBCO/MgO substrate with a relative dielectric constant of 9.8 and a thickness of 0.5 mm is used in the filter design process. The simulation results are in good agreement with the theoretical analysis, and can meet the design requirements.