Patent GB-1317175-A (GB)
Title: Radar unit and oscillator circuitry suitable for use therein
IPC: G01V3/12
Filed: 1970-06-03
Abstract: 1317175 Intruder alarms PEAK TECHNOLOGIES Ltd 25 Aug 1971 [3 June 1970 28 July 1970] 26858/70 and 36521/70 Heading G4N [Also in Division H3] In an oscillator comprising a microwave first oscillator such as a Gunn diode 40, Fig. 3, 70 Fig. 5, supplying an oscillating first output signal to a first load, such as an aerial 2 Fig. 3, and a second oscillator 80 arranged to oscillate at a second frequency different to the first frequency and the oscillatory output signal of which can exist independently of that of the first oscillator, an element, such as resonant cavity 41 and Gunn diode 40, forming part of the first oscillator 40, 70 and also part of the second oscillator 80 is adapted to respond to impedance changes on the first load 2 whereby changes in impedance loading of the first oscillator are detected by monitoring the variations, such as amplitude and/or frequency, in the oscillatory signal of the second oscillator. As shown the Gunn diode 40 and cavity 41 feed a microwave output from 3 which is radiated by the aerial 2 which has an expanded polystyrene cover 18. Reflections from an object, such as an intruder, alter the standing wave patterns received by the aerial 2 and this alters the amplitude and/or frequency of the oscillations produced by an inductance 80 which is mounted on a circuit board 4 external to the Gunn oscillator and produces oscillations of lower frequency e.g. at 1 MHz. The variations obtained from the output of inductance 80 are detected by diode 62 and transistor 83, are amplified in transistor 88 and cause transistor 95 to turn ON and transistor 100 to turn OFF so as to turn off a lamp 303 which may be at the front of the oscillator aerial arrangement at 14. This change in illumination of the lamp 303 is detected from a photo sensitive resistance or cadmium sulphide cell 304. A capacitor 301 introduces a delay so that the lamp 303 is not turned off by transients. Voltage regulation is provided by a transistor 77 and a Zener diode 73. The detection obtained from the transistor 83 (67, Fig. 4, not shown) may be indicated on a meter (68). In modifications of Fig. 5 (Figs. 6 and 7, not shown) feedback is used to maintain the lower frequency oscillations obtained from the inductance at a low level for maximum sensitivity and compensates for changes in supply voltage and temperature. A portion of the low frequency oscillation is rectified (111, 211) and amplified (109, 209) so to increase the supply voltage supplied to the cavity. This reduces the level of the low frequency oscillations and a state of equilibrium is reached. Three oscillator and aerial units of Fig. 3, may be suspended from a ceiling beam (200, Fig. 9, not shown) on a post so as to cover a circular area or alternatively this arrangement may be mounted on the floor. The light sensitive device 304 and lamp 303 may be as described in Specification 1,317,176 in which a screen arrangement composed of green and red filters or polarized filters are used to prevent light, e.g. from a torch of an intruder, incident on the indicator aperture of the lamp 303 from illuminating the photoelectric element. When movement in front of the aerial is detected by the radar unit the lamp 303 is turned off and this trips an alarm. The oscillator may be used with a Doppler system in which a Gunn diode is used as an oscillator mixer detector, the current changes being monitored by the second oscillator.