Narrow-band filter for the frequency range of 1.9GHz using double-sided YBCO films on 20-mm-square LaAlO{sub}3 substrates

摘要

Narrow-band microstrip hairpin-type filters are designed for wireless-communication applications. We have fabricated the high-T{sub}c superconducting filters by pattering 20-mm-square YBa{sub}2Cu{sub}3O{sub}y (YBCO) films. The double-sided YBCO films were grown on LaAlO{sub}3 (LAO) substrates by an off-axis magnetron sputtering system with two 2-inch-diameter sputtering guns. High-quality YBCO films within a 50-mm-diameter area were obtained. The homogeneous YBCO films revealed transition temperature T{sub}c(R=0) of ≥ 86 K and a critical current density J{sub}c (zero field) of ～1.5 × 10{sup}6 A/cm{sup}2 at 77 K. The surface resistance R{sub}s of ～ 1.8 μΩ was obtained at 77 K around 2180 MHz. The form of hairpin-resonator band-pass filter can be thought of as an alternative version of parallel-couple-resonator filter, except that the open-circuited ends of the resonator are folded back. Our 3-pole 20-mm-square filter has a 0.45-dB maximum insertion loss and 30 MHz bandwidth at 1.94 GHz both with the air-gap height of 3 mm. By mechanically changing the height of air gap between the filter pattern and the top housing plane, the center of frequency of the filter was varied from 1.92 to 2.0 GHz, corresponding to a frequency shift of about 5%. The influence of housing height on filter performance is discussed.