A compact high-temperature superconducting (HTS) low-pass filter (LPF) with an ultra-wide stopband and a sharp transition band is designed by integrating the fifth-order low-pass filter branch and closed loop cross-coupled (CLCC) microstrip structure. The fifth-order low-pass filter consists of two radial-stubs (RSs), one butterfly-shaped stub (BSs), and two T-shaped stubs (TSs), which can introduce five transmission zeros (TZs) with independently controllable frequency and position, so as to obtain good sideband suppression or upper stopband characteristics. The CCLC microstrip circuit is composed of cascaded high and low impedance microstrip lines, which can widen the width of the upper stopband and realize the ultra-wide stopband characteristic. The operating mechanism of the fifth-order LPF resonator and the CLCC microstrip structure are analyzed by the LC equivalent circuit models. The implemented LPF on a 0.5-mm thick MgO wafer with double-sided YBCO films demonstrates 1-dB cut-off frequency (f_c) at 2 GHz and 0.12 GHz narrow transition bandwidth from −1dB to −40 dB. The measured results show a 30-dB harmonic suppression from 1.08f_c to 11.7f_c i.e., above 23 GHz, a steep roll-off rate of 326 dB/GHz, an in-band insertion loss (IL) <0.10 dB, and a miniaturized size of 0.24λ_gc × 0.08λ_gc (λ_gc is the guided wavelength at the cut-off frequency).

通过集成五阶低通滤波器分支和闭环交叉耦合（CLCC）微带，设计了具有超宽阻带和陡峭过渡带的紧凑型高温超导（HTS）低通滤波器（LPF）结构体。五阶低通滤波器由两个径向短截线（RS），一个蝴蝶形短截线（BS）和两个T形短截线（TSs）组成，它们可以引入五个可独立控制频率的传输零点（TZ）和位置，以获得良好的边带抑制或较高的阻带特性。该CCLC微带电路由级联的高阻抗和低阻抗微带线组成，可以加宽上阻带的宽度，并实现超宽阻带特性。通过LC等效电路模型分析了五阶LPF谐振器的工作机理和CLCC微带结构。在具有双面YBCO膜的0.5毫米厚MgO晶圆上实施的LPF表现出在2 GHz和0.12 GHz从-1dB到-40dB的窄转换带宽下的1-dB截止频率（f _c）。测量结果显示，从1.08 f _c到11.7 f _c有30 dB的谐波抑制，即在23 GHz以上，陡峭的滚降速率326 dB / GHz，带内插入损耗（  IL）<0.10分贝，的微型尺寸0.24 λ _GC  ×0.08 λ _GC（λ _GC是在截止频率）的导波波长。