Filter subsystems for wireless communications

Thin-film oxide superconductor materials and advanced processing techniques have been used to fabricate high-performance filters for cellular communications base stations. Quasi-elliptic bandpass and band reject filters were designed and realized using microstrips to approximate lumped elements. These quasi-lumped resonators have achieved unloaded Q´s of more than 40,000. Precise system control allows for high operating temperature (77 K), using either Yttrium or Thallium high T/sub c/ compounds, compensating for temperature dependence. Such filters have been successfully integrated into a permanently evacuated dewar and cooled by a miniature Stirling cycle cooler. The cooler and dewar were integrated with control electronics which run off standard cellular base station +27 V power sources. The system consumes less than 100 W in operation, making it one of the most efficient HTSC subsystems demonstrated to date.