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A High Selective HTS Filter with Group Delay Self-Equalization for 3G Mobile Telecommunication Systems

A recent development of a twelve-pole high-temperature-superconducting (HTS) bandpass filter with group delay self-equalization for 3G wireless applications is reported. The filter is designed to have a 5.425 MHz pass-band at a centre frequency of 2121.5 MHz. The filter exhibits a quasi-elliptic function response implemented with a cascaded quadruplet (CQ) coupling structure. Two pair of complex frequency transmission zeros have been introduced to implement linear phase for group delay self-equalization. The filter was fabricated on a 0.5 mm-thick MgO wafer with double-sided YBCO films. The filter displayed a minimum insertion loss of 0.2 dB in the passband and a return loss better than 14 dB over the pass-band. Out-of-band rejection at both sides is higher than 57 dB with the skirt-slope as high as 100 MHz. The filter shows a 60 ns fluctuation of group delay within 78% pass-band which matches the requirement of TD-SCDMA standard of 3G mobile telecommunication.