GB877757A - Reactance amplifiers - Google Patents

Abstract

877,757. Parametric amplifiers. MICROWAVE ASSOCIATES Inc. Jan. 5, 1960 [Jan. 7, 1959], No. 397/60. Class 40 (9). A reactance amplifier comprises an elongated conductor 11 at least partially surrounded by an elongated conductor 10 the two conductors being coupled by a voltage-dependent reactance 12. The inner conductor is of such a length (e.g. #/4 that it may support a standing wave at signal frequency, the input and output circuits 28, 29 for the amplifier being positioned in the vicinity of the same voltage level of the standing wave. The pump frequency is connected via the coupler 14 to the voltagedependent reactance which may be a PN junction diode. The tuning capacitor C may be varied to adjust the resonance frequency of the cavity to that of the signal frequency. This capacitor may occupy the alternative position C<SP>1</SP>. In the embodiment shown the pump frequency is four times the signal frequency and the idler frequency (i.e. the difference frequency) is thus three times the signal frequency. With the presence of the inner conductor causing the propagation velocity to be the same for all these frequencies standing waves 35, 36, 37 are set up in the fundamental TEM mode for the signal, idler and pump frequency as shown in Fig. 2. The variable reactance 12 is situated at a point where the signal, idler and pump voltages are all appreciable, so that all these voltages may influence the reactor. In the absence of a pump frequency the energy is conveyed from input to output terminals without loss. In a modification, Fig. 3 (not shown), the inner conductor is telescopic and adjustable. One terminal of the variable reactor is then fixed to the moving part of the inner conductor and the other terminal is capacitatively coupled to the outer conductor. In a further modification, Fig. 4 (not shown) the outer cylinder is open ended and the inner conductor is doubled in length. Various other cross-sectional configurations for the conductors may be adopted, Figs. 5 . . . 8 (not shown). Although the apparatus may be dimensioned for idler and signal frequencies as mentioned above, the pump frequency may in fact be a multiple of the pump frequency mentioned.