This paper proposes a method of improving the accuracy of the attenuation constant estimate obtained by using the cross-spectral technique. In the cross-spectral technique, the envelope of the estimated impulse response is deformed due to the use of a time window. As a result, the estimated impulse response decays more rapidly than the real impulse response does, and the attenuation constant obtained by the estimated impulse response becomes larger than the real value. This paper first describes how the attenuation constant changes in the process of impulse response estimation. Next, we propose a method of improving the accuracy of the estimation. The effect of the proposed method is confirmed by computer simulation.

This paper describes on the transmission properties of the superconducting coplanar waveguide on LiNbO3 (LN) substrates, fabricated by YBa2Cu3Oy (YBCO) superconducting films. The films have been prepared by the reactive co-evaporation method and patterned by a wet etching process. The surface resistance of the obtained film was 0.04 Ω at 18 GHz and 77 K. It was confirmed from X-ray diffraction (XRD) that these films were highly oriented to the direction of c-axis without a secondary phase. The microwave transmission properties of these YBCO coplanar waveguides were investigated at frequencies up to 20 GHz and compared with that of the aluminum coplanar waveguide. The characteristic impedances of both coplanar waveguides were designed to be 50 Ω. It was found that the attenuation constants of these samples at 77 K were less than that of the aluminum coplanar waveguide for frequencies below 18 GHz.