Patent GB-585146-A (GB)
Title: Improvements in or relating to the determination of bearings and/or location of an object by electromagnetic waves
IPC: G01S1/24
Filed: 1942-04-21
Abstract: 585,146. Radiolocation systems. STANDARD TELEPHONES & CABLES, Ltd., and JACOBSEN, B. B. April 21, 1942, No. 5367. [Class 40 (v)] A radiolocation system comprises a number of transmitters arranged in a line and a number of receivers located at different observation points, each receiver comprising means for automatically graphically indicating as ordinates (or abscissµ) the difference in the lengths of the paths of signals received from each transmitter directly, and after reflection from an aircraft, against abscissµ (or ordinates) representing the distances of the corresponding transmitters from a reference point in the transmitter line. The form of the resultant curve, such as that shown in Fig. 2 or 4, is characteristic of the distance of the aircraft from the line of transmitters and changes as the aircraft moves, one particular form (illustrated in Fig. 4) serving to indicate approximately the vertical plane perpendicular to the line of transmitters in which the aircraft is at that time situated. An exact location of the aircraft may then -be effected at one or more of the most conveniently situated transmitters in conjunction with auxiliary receivers, or at the receiver at which the indication of the vertical plane is obtained in conjunction with an auxiliary transmitter. A large number of aircraft can be simultaneously dealt with. In the perspective diagram shown in Fig. 1, TT<1> represents the line of spaced transmitters, R the position of a receiving station, and A the position of an aircraft. RO is a perpendicular from R to the line TT<1>, AA<1> a perpendicular from A to the plane TOR, and AX<1> a perpendicular from A on to the line TT<1>. It is shown in the Specification that a curve, the abscissµ of which represent the differences XA+AR-XR between the paths of a reflected and direct signal from,a transmitter X to the receiver, the ordinates representing the corresponding values of the distance OX of the transmitter from the point O, will have one of the forms shown in Figs. 2, 3 and 4 according to whether the distance AX<1> of the aircraft from the line TT<1> is respectively less than, greater than, or equal to the distance OR of the receiving station from the line. In the first case the curve exhibits a maximum, in the second a minimum, and in the third neither. In all cases the curve asymptotes to two vertical lines, half the sum of the horizontal co-ordinates of which gives the length a of the line AR from the aircraft to the receiver, whilst the ratio of the difference /sum of these co-ordinates gives cos #, where # is the angle between this line and a line RS parallel to TT<1>. Further, as the curve passes through the form shown in Fig. 4, the vertical co-ordinate of the point of inflexion L gives half the value of the length OX<1>, so indicating the position of the vertical plane AX<1>A<1> perpendicular to the line TT<1> and containing the aircraft. The form of the curve therefore indicates whether the aircraft is at a distance from the line TT<1> greater or less than OR, and when it is that shown in Fig. 4, the pair of transmitters between which the plane AX<1>A<1> I is situated may be determined. Either or both of these transmitters, with auxiliary receivers or the receiver at the observation point together with an auxiliary transmitter, may then be used for exact location of the aircraft by known methods. In one form of the invention, pulse emitting transmitters spaced, preferably uniformly, along the line TT<1> are either switched on in succession or operate on different wavelengths and are received in succession by tuning the receiver. The directly-received pulse starts an oscillator which produces a horizontal time-base deflection of the beam of a cathode-ray indicator to which a vertical deflecting voltage corresponding to the position of the transmitter is also applied. The received reflected signal controls the beam intensity to produce a bright spot in known manner, the line of transmitters producing a succession of such spots lying on a curve similar to one of the forms illustrated. Alternatively, a frequency-scan method is used to measure the path difference, the frequency of the transmitters being continuously and cyclically varied, and the receiver producing an output voltage proportional to the frequencydifference of concurrently-received direct and reflected waves. In order that indications of a number of aircraft may be simultaneously given, the frequency output of the receiver may be scanned and the frequencies obtained applied to a frequency discriminator which produces an output voltage corresponding to each frequency. These voltages simultaneously deflect and control the intensity of the beam, thereby producing a spot for each of the aircraft.