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The surface resistance and surface reactance of high-quality YBa/sub 2/Cu/sub 3/O/sub 7/ superconducting films were determined from 10 GHz to 500 GHz using time-domain propagation measurements of picosecond electrical pulses on coplanar transmission lines. For the surface resistance, the authors find a square law dependence with frequency almost up to 500 GHz and a crossover of the losses of gold and YBa/sub 2/Cu/sub 3/O/sub 7/ films at 77 K at roughly 100 GHz. The pulse propagation is successfully modeled using the Mattis-Bardeen theory for the frequency-dependent conductivity of YBa/sub 2/Cu/sub 3/O/sub 7/. Good quantitative agreement of the surface resistance and surface reactance with this theory is obtained. The potential of YBa/sub 2/Cu/sub 3/O/sub 7/ superconducting films and equivalent gold and superconducting films for high-speed applications is studied theoretically.

The design and fabrication of high-T/sub c/ chirp-response tapped delay line filters are discussed. The key components in this development were long delay lines with more than 10 ns of delay, impedance transformers, and backward-wave couplers. All of the typical transmission line geometries were examined, including microstrip, coplanar and stripline. Designs were developed using microwave CAD routines and superconducting niobium delay line prototypes. Tapped delay line chirp filters with up to 12 ns of total delay have been successfully fabricated in YBaCuO.

Four-pole microstrip bandpass filters have been fabricated using both postannealed and in-situ-grown thin films of Y-Ba-Cu-O. The 4-GHz, 3% bandwidth filters exhibit, at 77 K, a passband insertion loss as low as 0.3 dB, compared with the 2.8-dB loss of similar gold metallic filters at the same temperature. These results demonstrate that complex passive microwave devices can be designed and implemented using high-temperature superconducting (HTS) material. More aggressive filter designs utilizing many more poles will result in much greater performance advantages for an HTS filter technology over a normal metal technology. Ultimately, ultrasharp-skirt filters can be produced, which would allow for more closely spaced communication channels and more efficient use of microwave communication bands than is currently possible with conventional filters.