A Novel HTS Compact Dual CT Structure Bandpass Filter

In this paper, a novel planar single spiral diamond resonator is designed, which is convenient to achieve the compact CT unit without the cross-coupling line for the filter design. By using this kind of CT unit, transmission zeros can be generated for improving the filter's selectivity and realize a miniaturized size, and also present an artistic three-dimensional sense. A 6-order novel high temperature superconducting (HTS) compact CT structure filter with passband covering 2 850~3 000 MHz is fabricated on the double-sided YBCO/LaAlO₃/YBCO thin film with the size of 13.5 mm×3.8 mm, the thickness of 0.5 mm and the dielectric constant of 24.1. The measured results show that there are two transmission zeros; the out-of-band rejection is greater than 45 dB/MHz; and the second-harmonic passband is located at 6 GHz, which means the filter possesses a wide stopband. The measured results agree rather well with the simulated ones.