Patent GB-1266329-A (GB)
IPC: G01S3/66
Filed: 1968-10-08
Abstract: 1,266,329. Radio direction finding; aerials. DEFENCE SECRETARY OF STATE FOR. 8 Oct., 1969 [8 Oct., 1968], No. 47654/68. Headings H4A and H4D. A direction finder has means for deriving and combining relatively adjustable portions of two beam-difference signals, having a double-lobed sensitivity pattern with a central null axis, Fig. 4. The signal from each of 24 identical aerial elements (A1-A24), Fig. 1, not shown, arranged on the circumference of a circle is split into eight paths by a series of hybrid elements (H1-H7), Fig. 2, not shown. One path from each of eight consecutive elements is fed to one of twenty four beam forming units (C1-C24), which combine the eight signals to produce sum signals (S1-S24) and difference signals (B1-B24), having sensitivity characteristics P 1 , P 2 , respectively. The twenty four difference beam signals B1-B24 which have null axes spaced equidistant around the azimuth plane are connected through gates G1- G24, Fig. 5, to two amplifiers 1, 2 one each for the even and odd gates. The gates are controlled by a timing unit T1 which opens one even and one adjacent odd gate at a time and is synchronized with a second timing unit T2. Between the outputs of the two amplifiers 1, 2 is connected a chain of resistors R1-R15 which has gates G25-G40, connected to successive junctions, feeding the output buffer amplifier which drives the vertical deflection plates of a cathode-ray tube display. The gates G25-G40 are controlled by timing unit T2. Initially gates G1 and G2 are opened thereby combining the signals B1 and B2 having null axes (r 0 ) and (r 1 ), Fig. 1, not shown, across the resistor chain. The timing unit T2 then opens gates G25-G40 successively, combining varying amounts of B1 and B2, effectively rotating the null axis from (r 0 ) to (r 1 ) in 1 degree steps. When the gate G40 is open, timing unit T1 closes gate G1, opens gate G3 and the gates G40-G25 are successively opened. The process is repeated for all twenty four beam difference signals producing a 360 degrees scan in 1 degree steps. The network of gates G25-G40 may be replaced by a mechanical spinning capacitative goniometer. The apparatus of Fig. 7 is a complete system for operating in three modes. In the continuous mode the selector 100 produces pulses on the STEP 1 line which drive the counters 102-104 corresponding to timing units T1, T2 in Fig. 5. The selector has an output for selecting clockwise or anticlockwise scanning and a reset which starts the scan from the reference axis r 0 , which is set by the shaft position encoder 109 and the position is shown on a digital display 112. Two ten bit digital numbers representing the position of the shaft encoder and the position of the scan as shown by the angle counter 101 are fed to a digital comparator 106 which sends a signal along the A = B line to restart the cycle, when the two positions are. equal. This signal may also be used to trigger the time base of a CRT display, or to produce a mark on the display. In the reciprocating mode, the apparatus scans across a thirty or sixty degree sector from the reference axis r 0 . After the required angle scan the CW/ACW line changes state and reverses the direction of scan. In the manual mode, the digital comparator 106 detects the difference between the positions of the reference axis r 0  and the position of scan. The resulting signal from the comparator 106 determines the direction of rotation until the two positions coincide when the rotation is stopped. In this mode the receivers 119, 120 would be connected to aural indicator means. The apparatus also has an assembly of gates and resistor networks to produce a separate scan from the twenty four sum signals S1-S24. In this case the two outputs from the receivers 119, 120 would be displayed on a double beam CRT.