Narrowband Y-Ba-Cu-O filter with quasi-elliptic characteristic

The compact meander-shape configuration of planar resonators is suggested f or applications in narrowband filters with quasi-elliptic characteristic. T he quasi-elliptic frequency response with two transmission zeroes at the ed ges of the passband is provided by the specific symmetry of the coupled res onators and is controlled by an appropriate choice of the resonator dimensi ons and the couplings between the resonators. The 12-pole quasi-elliptic fi lter with 0.5% fractional bandwidth at 1.775 GHz has been designed using me ander-line microstrip resonators and manufactured on a double-sided YBCO fi lm on a LaAlO3 substrate. The filter exhibited the in-band insertion loss l ess than 0.5 dB at T=60 K, the return loss of 20 dB, the out-of-band reject ion better than 75 dB, and 40 dB/MHz slope of the characteristic.