Characteristics and limitations of superconducting distributed amplifiers

This dissertation deals with various factors which determine the gain-bandwidth performance of a superconducting distributed amplifier. These factors could be divided in to two major groups, one due to the device characteristics and the other due to the distributed amplifier configuration. Amongst several superconducting active devices which have promise for high speed applications the Josephson Vortex Flow Transistor (JVFT) and the Superconducting Current Injection Transistor (Super-CIT) are suitable for high frequency linear amplification and are currently reproducible in the laboratory.;Both JVFT and Super-CIT are based on controlling flux motion in a long Josephson junction (LJJ). The low impedance nature of these devices limits the realization of a practical amplifier. A distributed amplifier is one possible technique for achieving a practical wide band amplifier.;The analyses made on the distributed amplifiers utilizing these devices reveals several constraints on the device parameters as well as on the parameters of transmission lines and the number of devices to be used. A design guideline has been laid out for evaluating performance potential of superconducting distributed amplifiers.;Time domain analysis made on the JVFT resulted in a gain-frequency relationship which is dictated by the spatial averaging in the device. Another effect of the spatial averaging is shown as a slow rate limitation which leads to fabrication parameters that yield optimum performance of the junction. The gain factor of an individual device depends on the junction geometry, the choice of materials, and the fabrication parameters. A field analysis program was developed and used to calculate the low frequency gain factor of four different geometries. Gain limitations in narrow junctions due to fringing of magnetic fields was observed in all the geometries.;The results of the analyses made on the device and the configuration were used to evaluate the gain-bandwidth characteristics of a JVFT distributed amplifier. It has been shown that for a particular type of junction there exists an optimum bandwidth obtainable from a JVFT distributed amplifier which is much smaller than the device cut-off frequency.