Patent GB-635701-A (GB)
Title: Improvements in or relating to radio direction finding systems
IPC: G01S3/14
Filed: 1947-01-10
Abstract: 635,701. Radio direction-finders. STANDARD TELEPHONES & CABLES, Ltd., and CLEAVER, R. F. Jan. 10, 1947, No. 971. [Class 40 (vii)] A radio direction-finder comprises a plurality 4n (where n is an integer greater than unity) of non- directional aerials spaced uniformly around the circumference of a circle, alternate aerials forming one array and the remaining aerials forming a second interlaced array, the arrays being connected to respective inputs of a doubleinput direction - finding receiver, alternate aerials in each array being coupled to the receiver in opposite senses. Two interlaced radiation patterns in the form of sinusoidal functions of n# (# being the direction of reception), are obtained, and the signals applied to the receiver are compared by suitable indicating means to enable an indication (having at least a n-fold ambiguity) of the azimuth angle # to be obtained. With the present system the spacing between aerials can be made greater than that in a conventional Adcock system, thus resulting in a greater signal strength, without introducing an excessive spacing error. The spacing between adjacent aerials of an array is preferably of the order of a half-wavelength; this condition, however, is not critical as the system has a broad-band characteristic. By a suitable choice of the factor n and the spacing of the aerials, the system may be arranged to have its maximum reception characteristic at some selected angle of elevation. Fig. 1 illustrates a system, for which n is 2, comprising two arrays 1, 3, 5, 7 and 2, 4, 6, 8, having radiation patterns as shown in Fig. 4 by the full and dashed lines, respectively. The array 1, 3, 5, 7 is connected through lines of equal length to the terminal 9, the alternate aerials 3 and 7 being connected with reversed polarity as shown by the transpositions. The aerials of the other array are similarly connected to the terminal 10, the terminals 9 and 10 being connected to the stator coils 14 and 15 of a goniometer in a direction-finding receiver of known design. Rotation of the search-coil 19 through 360 degrees corresponds to a rotation of the null direction through 180 degrees, i.e. 360 degrees/n, n here being 2, so that four ambiguities exist, half of which correspond to the normal 180 degree ambiguities obtained with the usual Adcock direction-finders. A sense-aerial 20 may be coupled to the receiver to remove these " reciprocal ambiguities; in this case since n is even, the output from 20 is applied to the receiver over a path equivalent to those coupling the other aerials to the receiver. When n is odd, a 90 degree phase-shift must be introduced into the output from the sense aerial. Instead of a goniometer and nullindicator, a twin-channel receiver and cathoderay tube to which signals corresponding to those obtained from the two arrays as described in Specification 490,940 may be used. The ambiguities may be resolved by the additional use of a prior-art direction-finder, which may, for example, use selected ones of the aerials of the main direction-finder to form a system of the normal Adcock type. Alternatively, two direction-finders according to the invention may be used, the characteristic numbers n for the two systems differing by unity. The two aerial systems are conveniently concentrically arranged and may employ a common senseaerial. In Fig. 10, the signals from the two systems are fed to the goniometers of receivers 74 and 78 having a common output circuit 92. The rotors 85 and 86 of the goniometers are coupled through gearing 90 and 91 to a pointer 83 which may be rotated above a 360 degree scale. If the systems supplying receivers 74 and 78 are N-fold and (N+1)-fold systems respectively, the gearing 90 and 91 is constructed to cause the rotors 85 and 86 to rotate N and (N+1) times respectively, for each complete rotation of the pointer 83. In only one position of the needle 83 will the outputs of both receivers be simultaneously zero; at this position, a null, indicative of the true bearing, will be obtained upon the indicator 92. In a modification of this system, described in the Provisional Specification, the search coils of the two goniometers are connected in series and only one receiver used. According to the Provisional Specification, a single n-fold aerial array may be used in conjunction with a cathode-ray display on an automatic radio compass in a system employing a continuously rotating goniometer. The aerial arrays described are also applicable to systems wherein the signals received from two arrays are modulated and combined to give a signal having a phase dependent upon the direction of reception. Specification 498,417 also is referred to.