S-c-S junctions as nonlinear elements of microwave receiving devices

2014 The analysis of possible phenomena in the superconductor-constriction-superconductor (S-c-S) junctions inserted into microwave circuits is carried out. The results of experiments in which properties of the junctions making them different in comparison with usual nonlinear microwave elements were studied are discussed. The characteristics of receiving devices such as amplifiers, detectors and converters operating on the basis of these phenomena are obtained. The limit characteristics of these devices in different regimes of operation are analysed and compared with experimentally achieved characteristics. It is shown that the noise properties of the receiving devices utilizing the S-c-S junctions close to ideal can be obtained for the frequencies lower than characteristic frequency of the junction. This frequency for known realizations of the S-c-S junctions (point contacts and thin film bridges of small dimensions) can reach of order of 500-1 000 GHz or in other words of the middle of the submillimeter waveband range. WIDE BAND DETECTION (II). 1. The introduction. 1.1 THE S-c-S JUNCTION AS AN « IDEAL » SUPERCONDUCTING ELEMENT OF THE RECEIVING DEVICES. The most of receiving devices utilizing Josephson effect realized for this moment are made on the basis of the S-c-S junctions. We define the S-c-S (superconductor-constriction-superconductor) junction [1] as a structure in which weak link of two superconducting electrodes is created in the form of short circuit section of the same superconductor as electrodes with effective dimension A less than coherence length 03BE. The point contacts (see the review [2]) and thin film bridges of small dimensions [3]-[8] are well-known realizations of the S-c-S junctions. It is not difficult to understand why the S-c-S junctions are wide-spread. The main requirements to nonlinear elements of superhighsensitive microwave receiver are the following. (i) The nonlinearity of high magnitude, for instance, maximum modulation coefficient for parametric elements (see, for instance [9]-[11]) or maximum curvature of i-v characteristic for detectors [12]. (ii) Low level of intrinsic noise. (iii) High cutoff frequency above which properties (i) and (ii) become get worse by some reason. The Josephson elements satisfy well the requirement (i). As it will be shown later the magnitude of nonlinearity of these elements is limited by fluctuations only. The intrinsic noise (requirement (ii)) is low for all known superconducting elements not taking into account flicker-effect at low frequencies in the point contacts [13] and granular superconductors [14]. Therefore the main parameter reasonable for comparison of different elements is the cutoff frequency. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/rphysap:019740090107900