Influences of Feed Structure on the Performance of Cross-Coupled Narrow-Band YBCO Filters

L. M. Wang；Chang-Hao Hsieh；Chih-Chang Chen；Jie-Fan Wu

Chinese Journal of Physics

43卷3S期（2005 / 06 / 01）

702 - 708

英文

Narrow-band microstrip cross-coupled band-pass filters based on the quadruplet geometry are designed for wireless-communication applications. The high-Tc superconducting filters were fabricated by patterning YBa2Cu3Oy (YBCO) films double-sided deposited on 20-mm-square and 0.5-mm-thick LaAlO3 substrates. Each of the half-wavelength resonators in the filter consists of loop-like inductor and two patch capacitors at both ends. The inductive coupling between the non-adjacent resonators produces transmission zeros in the frequency response. Due to the presence of transmission zeros near the pass-band edge, a steep skirt characteristic is exhibited in the frequency response. It is found that the filter performances are strongly affected by the feed geometries designed. We obtain an optimum feed structure for our 4-pole 20-mm-square filters, showing a 1.936-GHz center frequency with a 16-MHz bandwidth and a 2.2-dB maximum insertion loss at 77 K. The influences of feed structure on the filter performance are systematically investigated.