Patent GB-1458402-A (GB)
Title: Navigation or guidance and piloting aid system
IPC: G01S13/76
Filed: 1974-01-22
Abstract: 1458402 Radio navigation INTERNATIONAL STANDARD ELECTRIC CORP 22 Jan 1974 [22 Jan 1973] 02888/74 Heading H4D In a radio navigation system the position of a moving object, such as a ship, is determined by a fixed transmitter-receiver station, and the angular bearing (α) of said fixed station with respect to the axis of the moving object is determined by a transponder thereupon having a directional receiving aerial. The fixed station also comprises a directional receiving aerial and at that station the radial velocity of the transponder is determined as well as its angular position (#) and distance (#). The transmitterreceiver and the transponder each include modulating and demodulating means, whereby data can be exchanged between the fixed station and the moving object by the same radio link as that used for the said determinations. At the fixed station a data processing unit computes the position and direction of the moving object and its future position from measurements supplied by the transmitter receiver and from measurements sent by the transponder. The modulating means of the transmitterreceiver provide for transmission of said computed results of the transponder. The system may be applied to the piloting of ships along a channel leading to a port. In one embodiment a shore station has separate transmitting and receiving aerials 1<SP>1</SP>, 1<SP>11</SP>, Fig. 3, the former being fixed and providing a broad beam covering the area of interest, and the latter being rotatable and providing a narrow beam, whereby the bearing 0 of the transponder on a ship may be determined. A CW or pulse microwave radar transmitter 2 feeds the aerial 1<SP>1</SP>. It has a modulation input from a data processing unit 4, and supplies synchronizing and reference signals to a receiver 3. Said receiver is fed from the aerial 1<SP>11</SP> and provides inputs to the unit 4 representative of #, d#/dt, #, α, # being the distance to the transponder and d#/dt being its radial velocity. The unit 4 determines the ship's present position and direction and its future position by means of a pre-established mathematical model, taking into consideration the ship's characteristics, wind, currents, &c. The resulting data are used to modulate the transmitter 2, for communication to the ship. Transponder circuits 6 at the ship are associated with a directional aerial 5 and extraction circuits 8 whereby a modulating signal representative of the angle α is applied to the transmitting part of the circuits 6. In addition the circuits 6 demodulate data received from the shore station for utilization in a unit 7, which may be a display device. Finally, the circuits 6 provide a predetermined time delay between modulation reception and modulation retransmission. The extraction circuits may be included in the receiver of the transponder (Fig. 4, not shown) and a single aerial may be used at the shore station (Fig. 2, not shown). In another embodiment, the shore station comprises a pulse radar transmitter 2, Fig. 5, which operates on a frequency F1, and the ship station comprises a transponder which re-transmits on a different frequency F2. Separate aerials 1<SP>1</SP>, 1<SP>11</SP> are used at the shore station as in the embodiment of Fig. 3, the directional aerial 1<SP>11</SP> receiving the re-transmitted signals of frequency F2 from the transponder, and echo signals of frequency F1 from the ship's hull. Said signals of frequencies F2, F1 are separated by respective filters 11, 12 and are demodulated in respective receivers 13, 14. The receiver 13 also has a synchronizing signal input from the transmitter 2. It provides signals representative of α, #, # to a data processing unit 4, and a range pulse I#, corresponding to an echo at the range #, to the receiver 14. Said receiver also receives synchronizing and phase reference inputs from the transmitter 2. A signal obtained by phase detection and gated for the range # by the pulse I# is supplied to the unit 4. This signal is representative of the radial velocity d#/dt of the ship. Data are transmitted between the shore station and the ship in digital form, using pulse width modulation.