Narrow-band microstrip hairpin-type filters are designed for wireless-communication applications. We have fabricated the high-Tc superconducting filters by pattering YBa2Cu3Oy (YBCO) films deposited on 10-mm-square and 20-mm-squáre, 0.6-mm-thick LaAlO3 substrates. 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 10-mm-square filter has a 2.5-dB maximum insertion loss and 16 MHz bandwidth at 1.94 GHz, while 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 influences of wafer sizes and housing height on filter performance are discussed.
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