Fig. 1. Design, fabrication, and simulation results. (a) Schematic diagram of the HTS coupled resonator circuit; (b) simulated current density of the HTS coupled resonators’ circuit at the transparent frequency; (c) photograph of the HTS coupled resonator circuit; (d) schematic diagram of fabrication process of the HTS circuit; (e) simulated and theoretical transmission spectra of the HTS coupled resonator circuit; (f) simulated group delay of the HTS coupled resonator circuit. The YBCO film has a conductivity of 1.2×1014  S/m and a thickness of 600 nm. The substrate is MgO with dimensions of 34  mm×20  mm×0.5  mm, and its relative permittivity is 9.7077. Due to the very low loss of the substrate, the loss tangent during simulation is set as 0, and the loss is equivalent to conductor loss. The depth of the air layer below the top cover is 5 mm. The dimensions in the circuit are as follows: L1=34  mm, L2=20  mm, a1=0.48  mm, a2=0.36  mm, a3=0.08  mm, b1=2.56  mm, s1=0.8  mm, s2=7.2  mm, f=1.20  mm, w1=6.2  mm, and w2=8  mm. The number of turns of each spiral resonator is 12. The linewidth and line spacing are both 0.08 mm in the spiral resonators.

Fig. 2. Simulation study of EIT, ATS, and Fano resonance of the coupled resonators. (a) Simulated results of transmission spectra as s2 varies, and f is set as 1.02 mm; (b) simulated results of transmission spectra as f varies, and s is set as 7.2 mm; (c) simulated corresponding group delay in (a); (d) simulated corresponding group delay in (b).

Fig. 3. Experimental setup and results. (a) Schematic diagram of the measurement setup; (b) comparison between simulation and measurement results of the transmission spectra of the HTS coupled resonator circuit; (c) comparison between simulation and measurement results of the group delay of the HTS coupled resonator circuit; (d) measured results of transmission spectra as temperature varies; (e) measured group delay at the transparent frequency as temperature varies.