Patent GB-1455929-A (GB)
IPC: G01S3/48
Filed: 1974-11-19
Abstract: 1455929 Radio direction-finders INTERNATIONAL STANDARD ELECTRIC CORP 19 Nov 1974 [24 Nov 1973] 50093/74 Heading H4D  The Specification describes a method of radio direction finding using a plurality of antenna elements in which at least one group of two element pairs is provided, the elements of each pair being spaced the same distance apart, the pairs being arranged so that they either lie on the same straight line or on respective straight lines which are mutually parallel, the amplitudes (m1, m2, m3, m4) of the r.f. voltage picked up by each element being measured separately from the measurement of the phase differences (α1, α2) between the voltages picked up by the elements of each of said pairs whereby phase difference (#) of the wanted signal as received by each element of a pair with respect to the other element of the pair is determined from the equation In a first embodiment, three like, equally spaced aerial elements E2, E1, E3, Fig. 1, are located in a straight line. Wanted waves Wn are incident from a direction which is at an angle # to a perpendicular to the said straight line. If # is the phase difference between the signals received by the aerial elements E2, E1 or El, E3 then, = arc sin ##/2#a (# = wavelength, a= spacing between elements). If, in addition to the wanted waves, unwanted waves Ws occur, i.e., owing to reflection of waves radiated from the distant transmitter by an obstacle, the two waves add vectorially at each element as shown in Fig. 3. Here m2, ml, m3 are the resultant voltage vectors at the elements E2, El, E3, each constituted by a wanted signal n and an unwanted signal s, of smaller magnitude. The vectors n2, n3 relating to the elements E2, E3 are displaced in phase by # from the vector n1 relating to the element E1. The vectors s2, s3 relating to the elements E2, E3 are displaced in phase by γ from the vector s1, relating to the element E1. The amplitudes of the vectors m2, m1, m3 are measured, as are the phase angles α1, α2 between the vectors m2, m3 and the vector ml. The measurements may be made either simultaneously or sequentially. In the above embodiment, the element El is common to both pairs of elements, but in other embodiments four elements are used, providing two pairs E1, E2 and E3, E4. The equation for evaluating # then becomes, In another embodiment 2n aerial elements E1 to E2n, Fig. 8, are equally spaced around a circle and are associated with respective receivers R1 to R2n. Connected to the receivers is an amplitude and phase meter AP, which delivers the measured values, separately for each element, to a computer C. Said computer determines the angle # for two individual pairs of elements on the circumference, the elements of one group being diagonally opposite the elements of the other, and averages the results, in order to counter the effects of unwanted waves which may arrive from several directions which differ from the direction of the distant transmitter. Alternatively, a central element ME may be used in combination with every pair of diametrically opposed elements to form a plurality of threeelement groups for evaluation purposes. A test signal generator PS may be connected to the central element ME for sending calibration pulses to all the receivers R1 to R2n, when required.