Coupled-Cavity Traveling-Wave Parametric Amplifiers: Part II-Experiments

The filter-circuit approach to broadband travelingwave parametric amplification at microwave frequencies is described from an experimental point of view. The experiment revolves around a series of inductively coupled microwave cavities, each loaded with one variable-capacitance semiconductor diode. Gain-bandwidth products of 2000 Mc with a 350-Mc bandwidth at S band have been obtained by using commercially available diodes. Noise temperatures of 130°K have been measured. Based on the analysis of the companion paper, a qualitative prediction of the gain-frequency behavior is given. The experimental arrangement is set forth in some detail. It consists of a series of these coupled cavities with separate pump power distribution at each diode. Through this flexibility in pump phase shift and amplitude, a variety of advantages is achieved. The effects of the many variables on the performance of the amplifier are described. Several methods of achieving short-circuit stability of this amplifier are outlined. These are: 1) nonuniform pump phase shift between sections, 2) nonreciprocal loss with ferrites, and 3) nonreciprocal loss with upper pass bands. The experimental behavior of each method is shown, and the noise performance to date is briefly discussed.