Compact ultra-narrowband superconducting filter using N-spiral resonator with open-loop secondary coupling structure

Tao Lin, Wei Bin^†, Guo Xubo, Li Hongcheng, Luo Chenjie, Cao Bisong^‡, Jiang Linan

(a) Configuration of the feeding structure. (b) External quality factor Q_e versus D₆ and D₇.