High-Q tunable YBCO disk resonator filters for transmitter combiners in radio base stations

Results on the development of a tunable HTS resonator structure for transmitter combiners of radio base stations are reported. Design goal was the minimization of the dissipative insertion loss of a one-pole filter with a 3-dB bandwidth of 630 kHz under the impediment of a required tunability of the center frequency between 1.93 and 1.99 GHz and a power handling capability for 10 W transmitted power. At 70 K the quality factor of the utilized disk resonator structure turned out to be limited to 10(5) due to dielectric losses in LaAlO3 substrate, but in a lower temperature range where dielectric losses are no more dominating, Q(0) = 290,000 was obtained for the tunable version.