A theory of a unilateral parametric amplifier using two diodes

This paper describes the theory of a unilateral parametric amplifier which contains two variable-capacitance diodes separated by a quarter wavelength at the signal frequency and a half wavelength at the idler frequency. It is shown that a broadband signal circuit is essential in order to obtain unilateral gain, and that matching conditions are obtainable even with a high gain. The optimum noise figure is slightly worse than that of a single-diode reflection-type amplifier; however, this amplifier has advantages if it is refrigerated at liquid helium temperature, because it does not require a circulator in front of its input port. The amplifier usually requires an isolator at its output port, since it does not have substantial loss in the reverse direction.