Coupled-Cavity Traveling-Wave Parametric Amplifiers: Part I-Analysis

A general class of traveling-wave parametric amplifiers based on coupled-cavity filter circuits is described. This type of amplifier is particularly suited to microwave frequencies and incorporates new features that overcome some severe difficulties associated with other circuit structures. Traveling-wave diode-type amplifiers having relatively wide bandwidths and great simplicity at S band have already resulted from this approach (details of experiments will be described in Part II). An analysis is presented which provides detailed information on operating characteristics, including the effects of terminal impedances, reflected waves, circuit loss, etc., and also leads to a simple physical picture of the cumulative interaction mechanism in terms of coupled-mode concepts. This physical picture is emphasized throughout this paper. Gain bandwidth considerations are discussed in terms of a fundamental "interaction-impedance" parameter. Representative calculated curves show that unilateral gains of 12 to 15 db over relatively wide bandwidths are attainable with as few as 4 to 6 diodes. Methods of increasing the gain through use of ferrites and special circuit techniques are proposed.