Improved performance of unidirectional 4-frequency parametric amplifier

The noise figure of the 4-frequency parametric amplifier investigated can be lowered substantially by deviating from power matching, as is shown by experiments performed on a low-frequency-amplifier version. This adjustment has the additional advantages of providing a larger gain-bandwidth product, an improved gain stability and a higher gain saturation. The theoretical optimums in minimum noise figure, maximum bandwidth and the associated gain stability are calculated for the case when power mismatching is permissible, and the results are compared with the experimental values and with the theoretical performance of the reflection-type amplifier employing a circulator.