Microwave amplification by means of intrinsic negative resistances

Intrinsic-negative-resistance amplifiers with matched input, known for some time at low frequencies, are easily transposed at microwave frequencies. With amplifiers based on the parallel coupling of load and negative conductance, a unidirectional line can ensure or improve separation between input and load. In another circuit a circulator is used. The two-way amplifier, consisting of a T-network, can be so realized that matching persists if the two negative conductances vary in common. The gain of any negative-resistance amplifier is practically limited by the diminution in amplitude stability, the increase in harmonic distortion and the reduction in bandwidth. In the best cases, the expressions defining the limiting quantities contain the gain to the power of one-half. The noise figure increases as a linear function of gain in the case of the previously matched circuit, but does not depend on the gain in the other circuits. Although the main importance of negative-resistance amplifiers is in connection with molecular and parametric devices, electronic valves, designed at the outset as oscillators, may be used. Their most promising application seems to be high-power amplification.