The large capacity handled by the IMT 2000 requires that a high-frequency band of 2 GHz be used. However, raising the frequency results in the occurrence of various problems related to the large volume of data handled, such as increased signal loss, lower signal quality and interference in adjacent frequency bands. It is hoped that substituting a high-temperature superconductor in a place of the existing dielectric filter will reduce insertion loss, noise and high Q values. The authors have applied current technologies for film, microwave and cryocooler to develop a high-temperature superconducting (HTS) filter subsystem for the base stations of mobile telecommunication systems. The new filter has a fractional bandwidth below 1.02% at 1.955 GHz and has a minimum insertion loss at 0.2 dB. A small, highly efficient and long-life pulse-tube cryocooler a with cooling capacity of 0.65 W at 70 K and 60 W compressor input power is used 60 W. The components have been integrated into a subsystem, the external dimensions of which have a total volume of 10.1 L.
