Patent GB-1262591-A (GB)
Title: Microwave apparatus employing a capacitively coupled solid-state negative-resistance device
IPC: H03B9/14
Filed: 1969-01-27
Abstract: 1,262,591. Negative resistance oscillator circuits. D. A. PEARS. 27 Jan., 1969, No. 4516/69. Heading H3T. A microwave oscillator has a solid state negative resistance device 12 mounted in a resonant cavity 3 so as to extend from a wall of the cavity, one of the terminals of the device has no direct electrical contact with the cavity and the device is, during operation, only capacitively and inductively coupled to the cavity at the operating frequency and a bias circuit 16 is connected to the one terminal through a conductor 14 which is coupled to the walls of the cavity by a by-pass capacitor 15 and presents an electrical length which is an odd number of quarter wavelengths at the operating frequency between the device and the by-pass capacitor. The device 12 may be an avalanche or Gunn effect or L.S.A. mode diode. In Fig. 1 the device 12 may be of mesa construction mounted in a metal ceramic package with the surface of the mesa bonded to the end of a stub 13 which is used for a heat sink and is connected to an upper wall 8 of a rectangular cavity resonator 2. The body 2 of the resonator may be copper, aluminium or " Invar" (Registered Trade Mark). The device 12 is reverse biased by a potential applied via terminal 16 and a helical inductance 14 which presents a high impedance to r.f. currents. The energy is taken off via coupling slot 24 via a wave-guide connected to flange 4. The oscillator and resonator may be tuned by varying the position of post 6 by adjustment to screw 21. A capacitance gap 11 is formed between the end of port 6 and a wall 8 of the cavity 3. In a modified arrangement (Fig. 4, not shown), the device 12 is mounted transversely to the post 6 which is in the form of a conductive post (29) which slides axially through a segmented sleeve (31). In a further modification having a cylindrical cavity (33, Fig. 6, not shown), the output oscillations are taken off by a coaxial line 37. In another embodiment (Fig. 10) the bias is applied via the central conductor 62 of a r.f. coaxial line 61 which is tuned by an axially slidable copper or brass annular tuning slug 64 mounted on a pair of insulating sleeves 65 and 66. The capacitive tuning slug 64 is adjusted so that the coupling at the microwave frequencies between terminal 16 and the cavity 3 is less than 25%. In a further embodiment (Fig. 11) the bias circuit is coupled from the terminal 16 via a conductor 68 metallized or bonded on to a dielectric printed circuit board 67, of glass or "Teflon" (Registered Trade Mark) to the device 12. The conductor 68 has an annular ring portion (72, Fig. 12, not shown) connected to the device 12 and may be formed by conventional printed circuit techniques. The oscillator may be used as the local oscillator for a balanced mixer of an a.m. f.m. radio receiver and results in reduced noise. The microwave oscillator enables a portion of the circulating current around the device 12 to be by-passed, so as to decrease the coupling between the device 12 and the cavity, 3 by a divider network around the device 12 consisting of series and shunt impedances (Z1, Z2 and Z3, Fig. 13, not shown). Specifications 1,216,880 and 1,070,261 are referred to.