Patent GB-1509426-A (GB)
Title: Radioelectric system for determination of the orientation of a moving body
IPC: G01S13/76
Filed: 1975-05-21
Abstract: 1509426 Transponder beacon system INTERNATIONAL STANDARD ELECTRIC CORP 21 May 1975 [21 May 1974] 21910/75 Heading H4D In a secondary radar type system, the coded response signal, from a multi-element transponder mounted on a station having an orientation axis, e.g. a ship's heading direction, received at the interrogating land-based radar station, e.g. in a harbour at point P in Fig. 1, contains information which is extracted to give the value of the angle subtended by the orientation axis and a line intersecting both stations from which may be calculated, e.g. the magnetic bearing of the interrogated ship's heading direction. This value may then be communicated to the ship. As described the transponder comprises an arrangement of eight microwave horn systems Al to A8, Fig. 4, covering 360 degrees. Each hom system, e.g. Al, Fig. 3, comprises a reflecting short circuit Cl, and a phase shifting circuit controlled by a signal generator G I of frequency f1. A received interrogating radar signal at frequency F is phase modulated and retransmitted from the horn system at frequency F' +f1 where F' is the Doppler shifted radar interrogation signal frequency due to the motion of the ship. The angle between the boresights of all adjacent horn systems, e.g. A1 and A8, is 2α, which is known. Horn systems A1 to A8 respectively retransmit the interrogating signal modulated by known frequencies f 1  to f 8  whereby the retransmitted signals received at the radar station having the two largest amplitudes are used to identify an adjacent horn system pair, e.g. Al and A8 and the relative values of these two largest amplitude signals is used, in the case of systems A1 and A8 the bisector of the electrical axes of which corresponds to the ship's heading line MU to determine the angle #, Fig. 1. In the case where another horn pair, e.g. A5 and A6 retransmitting signals at frequencies F' + f5 and F<SP>1</SP>+f6 respectively, produce the largest amplitude received signals at the radar station, their relative amplitudes define a line (XX', Fig. 5, not shown) bisecting their respective electrical axes, but at a known angular relationship (i.e. 135 degrees, see Fig. 5, not shown) with the ship's heading direction MU which direction may be thereby calculated, at the harbour radar station, which comprises a rotating antenna 5, Fig. 3, a Doppler radar transmitter 3, a receiver 4, a frequency selection and amplitude detection circuit 6 which furnishes the amplitude of the received signals at frequencies F<SP>1</SP>+f1 and F<SP>1</SP>+f8, and a computer 7 which may comprise an amplitude discriminator (9, Fig. 6, not shown) which selects the two highest amplitude frequency components, e.g. F' +f5 and F' +f6. A decoding circuit (10) generated the angular difference between, e.g. line XX' and the heading direction MU, whereby the angle #, Fig. 1, may be calculated, and from which the ship's magnetic heading angle γ may be calculated. In other embodiments, each horn system amplitude modulates the retransmitted interrogation signal, and the transponder may be mounted ashore.