A high temperature superconducting filter for future mobile telecommunication systems

This paper presents a narrow-band high temperature superconducting (HTS) bandpass filter of Yba₂Cu₃O₇ (YBCO) 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 (QCT) coupling topology is discussed. The filter is designed to have a 10 MHz pass band in the UMTS basestation receive band. The filter substrate was a sapphire wafer measuring 47mm × 17mm × .43 which had a double sided thin film coating of YBCO. The filter displayed a midband insertion loss of .6 dB at 1.970 GHz and a return loss better than (-10dB preliminary) over the pass band. A high performance out of band rejection associated with quasi-elliptic filter function was also recorded.