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) Coupled N-spiral resonators with OLSCSs (S = 1.80 mm, D1 = 5.60 mm, D2 = 6.00 mm). (b) Coupling coefficient versus the lengths of D1 and D2 of the OLSCSs (S = 1.80 mm).