ISSTT Proceedings

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Theoretical and Practical Limits on the RF Bandwidth of SIS Mixers

Authors:
A.R. Kerr
Abstract:
Most millimeter-wave mixers have an RF equivalent circuit that falls into one of the following categories: (i) Parallel R-C (the junction) connected to a resistive source with no broadband matching circuit. (ii) Parallel R-C, and possibly series L, followed by a broadband matching circuit. (iii) Parallel R-C-L, and possibly series L, followed by a broadband matching circuit. This paper examines the maximum (RF) bandwidths achievable by SIS mixers in each of these categories. Fundamental limitations on the matching bandwidth between a resistive source and a capacitive load were derived by Bode in 1945. In 1950, Fano developed a more general theory which included capacitive devices with series inductance. To use the work of Bode and Fano to determine the useful bandwidth of a practical mixer, it is necessary first to know the range of (complex) source impedances within which acceptable performance is obtained. From SIS mixer theory it is found that acceptable performance results when the magnitude of the source reflection coefficient p, relative to the optimum source impedance, is less than some value. For Nb/A1-Al203/Nb SIS mixers in the 70-350 GHz range, |[rho]| [less than or equal to] 0.4 appears appropriate.
Categories:
SIS
Year:
1994
Session:
8
Full-text:
Download a PDF of this paper.
Page Number(s):
548-557