Miniaturized Ultra-Narrowband Superconducting Microstrip Filter With Stable Coupling Using Optimized Twin Spiral-In-Spiral-Out Resonators

Suppression of spurious harmonic responses in superconducting microstrip spiral filters using gold overlay and stagger tuning

“…One design is a meander line joined to an IDC (Figs. 3 a and b ); another is the spiral‐in‐spiral‐out resonator (SISO) [31, 32] (Fig. 3 c ).…”

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

“…Twin-spiral and twin spiral-in-spiral-out resonators have been employed to design filter with ultra-narrow bandwidth. [9][10][11][12][13][14][15][16] Tao et al proposed modified twin-spiral and twin spiral-in-spiral-out resonators to realize weak couplings and designed two compact ultranarrowband filters with FBWs of 0.08% [12] and 0.18% [14] in S band. Moreover, another inspiring method that adding secondary coupling structures between resonators to reduce coupling has also been investigated.…”