Patent GB-977236-A (GB)
Title: Microwave amplifier
IPC: H03F3/12
Filed: 1963-04-08
Abstract: 977,236. Tunnel diode amplifying circuits. BENDIX CORPORATION. April 8, 1963 [April 18, 1962], No. 13912/63. Heading H3T. [Also in Division H1] A wide-band microwave amplifier for a radio receiver comprises a tunnel diode 18, Fig. 1, one terminal of which is coupled to one port 16 of a ferrite circulator 1, to the other ports 12, 24 of which are respectively connected the receiving aerial 10 and mixer stage 26. The other diode terminal is earthed for high frequencies by capacitor 38, 38<SP>1</SP> and for low by capacitor 40, both of which are located as close as possible to the diode, the lead being series resonated by means of an adjustable stub line 20 and the whole parallel resonated by means of adjustable stub line 22. The diode is provided with an adjustable D.C. bias from a source connected to terminal 28, the voltage being reduced by means of a first potentiometer comprising resistors 30, 32 and smoothing capacitor 34 and a second adjustable potentiometer comprising variable resistor 36 and fixed resistor 42. According to the invention the length of the lead connecting the tunnel diode 36 to the circulator 14 is kept to a minimum, being less than a quarter wavelength long at the operating frequencies. In one embodiment the components of the amplifier are mounted on a housing block 43, Figs. 2, 3, the bias voltage being applied to jack 44 between which and a terminal 47 is connected resistor 30. Resistor 32 and capacitor 34 are connected between terminal 47 and earth terminal 48, and variable resistor 36 is attached to a side wall of the housing, being connected between terminal 47 and capacitor plate 38. The high-frequency by-pass capacitor 38 comprises mica dielectric 38<SP>11</SP> and earth plate 38<SP>1</SP>. The series tuning stub 20 includes a screwdriver-adjusted threaded member 50 movable axially along conductor 51, while the parallel connected stub 22 comprises a printed circuit board 52 having a dead end arcuate conductor pattern contacting conductor 54 which supports the tunnel diode 58. The effective length of the arcuate conductor is varied by means of a lever 56 pivotable on a collar forming part of earth plate 38<SP>1</SP> and including a spring conductor member 58 riding on the arcuate conductor. Lever 56 is moved by means of a threaded handle 60 whereby it may be locked in final position. In the ferrite circular 14 (see Division H1) which comprises a housing 61, Fig. 3, connected to the amplifier housing 43, connecting pin 62 projects into bushing 64 and so makes contact with arm 66 of Y-shaped conductor 68. In a modification (Fig. 5, not shown) the components of the amplifier are housed in a recess in the wall of the circulator and include a button type H.F. by-pass capacitor. The parallel tuning stub is, however, mounted inside the circulator housing and comprises a rod attached to the arm of the Y-shaped member, over which slides a tubular member bearing a set of spring fingers making contact with the rod; this member passes through a further tubular member set in the housing wall and can be locked in position by means of a set-screw.