GB887628A - Parametric amplifier - Google Patents

Abstract

887,628. Parametric amplifiers. HUGHES AIRCRAFT CO. June 20, 1960 [June 25, 1959], No. 21615/60. Class 40 (9). A parametric amplifier comprises a non-linear capacitance device fed by pump and signal energy respectively over two transmission means which are provided with filters for preventing the propagation of idler energy either to the signal output or the pump input, and for preventing pump energy from reaching the signal output. As shown schematically in Fig. 1, signal energy is supplied to and extracted from a circulator 14 via a tuning section 15 and a T-section 16 to a filter 17 and a phase-adjuster or " linestretcher " 18 to a further T-junction 21 whence the energy is supplied via a further phaseadjuster or line stretcher 38 to a crystal diode 37. Pump energy is also supplied to the crystal diode from a source 26 via an isolator 27, a timer 28, a filter 29 and phase shifter or line stretcher 31. In the case of signal, pump and idler frequencies of 2.5, 6 and 3.5 Gc/s. respectively, filter 17 is a low-pass filter of cut-off frequency 3 Gc/s. and the filter 29 is a high-pass filter of cut-off frequency 4 Gc/s. If the pump frequency is 3 Gc/s. with signal and idler frequencies 2.5 and 3.5 Gc/s., then filter 17 is still of the low-pass type and filter 29 is of band-pass type, the pass-band being centred on the pump frequency. The line stretcher 31 is adjusted so that signal energy reflected from the filter 29 reinforces that arriving directly at the T-junction 21. The line stretcher 18 is similarly adjusted in respect of reflections of the pump energy from the filter 17. Stretcher 38 is adjusted to ensure that the portion between the diode 37 and the filters resonates at the correct idler frequency. Bias for the diode is provided via a low-pass filter 42, so arranged to produce infinite impedance across the line 16 at signal frequency. A more detailed construction is given for the case where the transmission lines are coaxial lines, including a method of mounting the diode, Fig. 4. The central conductor 68 is tapered towards the diode 61, for impedance matching purposes. The cap 64 is similarly tapered internally and is provided with an end portion 71 for terminating the other end of the diode.