GB593017A - Improvements in or relating to wireless systems - Google Patents

Abstract

593,017. Radiolocation. WATT, R. A. W. Sept. 17, 1935, No. 25770. [Class 40 (v)] Aircraft, marine craft, or other objects are located by radiating intermittent carrier wave pulses and receiving in an indicating receiver the pulses reflected or re-radiated from the object. The primary radiation may be broadcast through large solid angles, and the receiving aerials may be designed to accept waves from corresponding angles, to avoid the necessity for searching for the object. The solid angles may be restricted to minimize interference from unwanted signals and atmospherics. The receiver and transmitter may either be adjacent or separated in space; and observation is taken of the time delay between a pulse received directly from the transmitter and a pulse received after reflection. If the pulse duration is longer than this time delay, the two received pulses are superposed, and the delay is measured from the beginning of the direct pulse to the change in amplitude caused by the superposition of the reflected pulse. The azimuth and elevation angles are determined by direction finding on the reflected waves. The vertical and horizontal dimensions of the object may be approximately determined by using waves of corresponding polarization, and by variation of the emitted wavelength until maximum response is obtained. If the object is a friendly craft, or a meteorological balloon, it may be provided with resonant radiators to increase the re-radiated energy, which may be keyed or modulated for identification or other purposes. Fig. 6 shows a suitable transmitter aerial array for giving radiation of low elevation and with a cardioid polar diagram in the horizontal plane. It comprises a stack of horizontal half-wave dipoles A ... F spaced half a wavelength apart in the vertical direction, and backed by a corresponding stack A<1> ... F<1> a quarter-wavelength behind. The receiving array may be similar, and it may comprise also a second array at right angles to the first, the two arrays being used as crossed pick-up systems of an aural or visual direction finder. Two receiving systems of this kind may be set up at a suitable distance apart as shown in plan in Fig. 8, and the angle of elevation of incoming waves determined by known means by comparison of the electromotive forces induced in the arrays. The stacks in the forward and rear arrays may be coupled to radiogoniometers, the search coils of which are mechanically linked, and are coupled together through phase-changing devices to a crossedcoil transformer serving as a phase-comparator. The single receiver thus fed from the two arrays is arranged to produce vertical deflection on a C.R. tube in which horizontal deflection is provided by a time base operating at pulse frequency, thus giving a range indication. By rotating the search coils, the echo pulse may be made to disappear at an angular setting which gives the azimuth of the reflecting object. These search coils are then re-set close to the angle of maximum response, and the third search coil rotated until the echo pulse disappears, its reading then being a measure of the angular elevation of the object. By employing two range-finding systems, the position of an object may be fixed by triangulation. If the range of an object is already known, the system may be used to measure the velocity of radio waves. Specification 252,263, [Class 40 (v)], is referred to.