Patent GB-1076808-A (GB)
Title: Improvements in or relating to parametric amplifiers
Inventor: SEIDEL HAROLD
IPC: H03F7/04
Filed: 1964-11-18
Abstract: 1,076,808. Parametric amplifiers. WESTERN ELECTRIC CO. Inc. Nov. 18, 1964 [Nov. 22, 1963], No. 46906/64. Heading H3B. A non-reciprocal parametric amplifier comprises two interconnected 3 db hybrids 10, 11, Fig. 1, having conjugate pairs of branches a-b, c-d and a<SP>1</SP>-b<SP>1</SP>, c<SP>1</SP>-d<SP>1</SP> respectively, the input signal frequency being applied to branch a of hybrid 10 and the output taken from branch b, while the corresponding branches a<SP>1</SP>, b<SP>1</SP> of hybrid 11 are connected to respective resistive and reactive terminations for the sideband frequencies of the amplifier. Variable reactances 12, 13 connected to a pump frequency source 14 are included in the circuits interconnecting the branches c, c<SP>1</SP> and d, d<SP>1</SP> of the two hybrids. The 3 db hybrids have the property of dividing equally between the two branches of a conjugate pair the incident power applied to any one branch of the other pair, and in Fig. 1 the hybrids are additionally of the quadrature type so that a 90 degrees phase shift is obtained between input signals and reciprocal output signals passed by hybrid 10 into branches c and d. The combination of these signals with the pump frequency at the variable reactances produces upper and lower sidebands fu=fp+fs and fl=fp-fs, where fp is the pump frequency and fs the signal frequency. Further phase changes occur when these sidebands in branches c<SP>1</SP>, d<SP>1</SP> are combined in hybrid 11, the upper and lower sidebands fu, fl due to the input signal being applied through filters 15 and 18 to a reactive termination and a resistive termination respectively, while the upper and lower sidebands due to the reciprocal output signal are applied through filters 17 and 16 to a resistive termination and a reactive termination respectively. Parametric amplification is obtained only under the conditions when the upper sideband circuit is reactively terminated and the lower sideband circuit is resistively terminated, and since these conditions only apply for the input signal frequency in branch a this signal is amplified and the reciprocal output signal in branch b absorbed. A strip line amplifier is described, Fig. 2 (not shown), in which the variable reactances are varactor diodes (40), (41) respectively associated with strip lines in different planes, the diodes being connected to two parallel ground planes 21, 22 between which the strip lines are located. The hybrids (20), (30) are formed by overlapping regions of the two strip lines and the resistive and reactive terminations comprise adjustable shorting members (54)-(57). Bandpass filters (44), (45) and (50)-(53) are each formed by a section of insulated conductor, and rejection filters (46), (47) consist of one-quarter wavelength openended stubs. Figs. 3 and 4 (not shown) use 180 degrees hybrids, the circuit in Fig. 3 using two 180 degrees hybrids in combination with 90 degrees delay networks (62), (23) in each of the branches c, c<SP>1</SP>, and the Fig. 4 arrangement using a 90 degrees hybrid 10 and a 180 degrees hybrid (61) in association with a 90 degrees delay network (70) between the pump source (70) and one of the variable reactances (71). The reactances may alternatively be variable reactors.