Compact wide stopband superconducting bandpass filter using modified spiral resonators with interdigital structure<xref rid="cpb_27_6_068502_fn1" ref-type="fn">*</xref><fn id="cpb_27_6_068502_fn1"><label>*</label><p>Project supported by the National Key Scientific Instrument and Equipment Development Project, China (Grant No. 2014YQ030975) and the National Natural Science Foundation of China (Grant Nos. 61371009 and 61401282).</p></fn>

Compact wide stopband superconducting bandpass filter using modified spiral resonators with interdigital structure**

Project supported by the National Key Scientific Instrument and Equipment Development Project, China (Grant No. 2014YQ030975) and the National Natural Science Foundation of China (Grant Nos. 61371009 and 61401282).

Wu Di¹, Wei Bin^{1, †}, Li Bo¹, Guo Xu-Bo¹, Lu Xin-Xiang², Cao Bi-Song¹

Potentials (+ and −) and current directions (arrowed) of a rectangular-spiral resonator at (a) fundamental resonant frequency and (b) the first spurious frequency. Potential distributions of an interdigital structure located at the end of a resonator at (c) fundamental resonant frequency and (d) the first spurious frequency. Dashed ellipses represent other parts of the microstrip line of the resonator, and other fingers of the interdigital structure are represented by the ellipsis in the middle.