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The paper reports a recent development of a narrowband high temperature superconducting (HTS) bandpass filter for future mobile communication systems. The filter is designed to have a 5 MHz passband in the UMTS base station's receive band. The filter exhibits an 8-pole quasi-elliptic function response implemented with a cascaded quadruplet coupling structure. The filter was fabricated on a 0.43 mm-thick sapphire wafer with double-sided YBCO films. The measured filter showed a midband insertion loss of 0.5 dB at 1973 MHz and a return loss better than À15 dB over the passband. It also exhibited an excellent rejection over the entire UMTS base station transmission band.

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This paper presents a narrow-band high-temperature superconducting bandpass filter on a sapphire substrate applicable to future mobile communications systems. The design and simulation of a ten-pole quasi-elliptic function filter implemented using a cascaded quadruplet trisection coupling topology is discussed. The filter is designed to have a 10-MHz passband in the Universal Mobile Telecommunications System base-station receive band. The filter substrate was a sapphire wafer measuring 47 mm 17 mm 43 mm, which had a double-sided thin-film coating of Yba 2 Cu 3 O 7 . The filter displayed a minimum insertion loss of 0.2 dB in the passband and a return loss better than ( 12 dB preliminary) over the passband. A high performance out-of-band rejection associated with a quasi-elliptic filter function was also recorded.