Patent GB-1084969-A (GB)
Title: Improvements in radar-navigation systems
IPC: G01S13/937
Filed: 1965-06-03
Abstract: 1,084,969. Radar. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. June 3, 1965 [June 5, 1964], No. 23719/65. Heading H4D. A shipborne radar navigation system comprises a P.P.I. display, wherein a marker can be made to follow the response of a ship, assuming a constant velocity and bearing for the ship, and wherein predicted course lines can be projected from said marker assuming either said constant velocity and bearing, or any other velocity and bearing. Fig. 1 shows a radar antenna AT, transmitter/receiver RA, and a ship's heading up P.P.I. display tube BB, together with the scanning and marker circuits for the Y direction deflection coil DS. The circuits for the X direction deflection coil are substantially identical. A resolver AB, connected to the antenna produces signals Sin # and Cos # where # is the azimuth angle of the antenna. The Sin # signal is supplied to the X direction deflection coil circuits and the Cos # signal is fed via a switch C2, normally closed during the echo return period, to the input of an amplifier A 1 . During the echo return period a feedback capacitor C converts the amplifier A 1  into an integrator, such that it produces, at its output, for application to the deflection coil DS, a sawtooth signal with a slope proportional to Cos #. The X direction deflection coil is similarly provided with a sawtooth signal with a slope proportional to Sin #. A rotating, radial, P.P.I. scan is thus produced. The sawtooth signal is stopped at the end of the echo return period by the closure of switch C 4 . Switch C 4  is reopened at the start of the next echo period, and, together with switches C 1 /C 3  is under the control of pulse generator KL. To operate switches C 1 /C 3  generator KL generates a pulse at suitable intervals, starting just after the end of an echo period, and ending at the end of the next echo period. This pulse, for its duration, closes switch C 1 , opens switch C 2  and closes switch C 3 . The marker circuits comprise a plurality (one for each response) of object units DE comprising six potentiometers-only the three Y direction potentiometers P 1 , P 2  and P 3  being shown. The initial position Y 0  of the marker in the Y direction is determined by the setting of potentiometer P 1 , which produces a signal which is fed, via switch C 1 , after the echo period, to the deflection coil DS. A sinusoidal signal from generator G is superimposed on the signal, such that, in combination with a quadrature signal similarly superimposed on the X direction signal, a circle is described on the display tube in a position variable by potentiometer P 1  &c. A second potentiometer P 2  gives an output representing the velocity Vy of the selected ship in the Y direction, which output is fed to a third potentiometer P 3 . This has a wiper which moves from one end of its travel to the other at a uniform rate in half an hour. The output of potentiometer P 3  thus represents Vy.t and is accordingly fed to the deflection coils DS-the total deflection signal thus giving a Y direction position of (Y 0 +Vy.t). The wiper of potentiometer P 3  is thus returned to its t=0 position, and the circular marker is aligned on the response by varying potentiometer P 1 . After an interval, potentiometer P 2  is adjusted to bring the marker back on to the response, whereupon the marker will follow the response, if the' target ship retains its velocity and bearing. To produce the predicted course line a manual switch LW is closed such that the velocity signal from potentiometer P 2  is fed via switch C 3  to amplifier A 1 . The closure of switch C 3  extends over an echo period, during which period switch C 4  is open and the amplifier acts as an integrator. The velocity signal thus produces a sawtooth signal which is added to the signal from potentiometers P 1  and P 2  to produce a course line on the display. The course line is in a series of dots, due to periodic blanking of the display, the distance between two dots representing predicted distance travelled in a known time, such that time to closest approach &c. information may be determined from the display. To produce a predicted course line resulting from a change of own ship's speed from V to (V + #v) and a change of own ship's heading of a, a signal representing (- #V + 2 sin<SP>2</SP>α/2(V+ #V)) must be added to the velocity signal from potentiometer P 2 , and a signal representing ( - (V+#V) sin α) must be added to the corresponding signal' in the X directions circuit. To do this, manual switches MN 1  and MN 3  are closed. Velocities - 8V, + #V, +V and - V are set up by potentiometers P 4 , P 5 , P 6  and P 7  respectively. The - 8V signal is fed to switch MN 1  via resistor R 3  to give - 8V and the + #V and + V signals are fed via potentiometers R 4  and R 5  respectively, gauged and arranged to give an output of +2 (V+#V) sin<SP>2</SP>α/2. Potentiometers R 6 , R 7 ,   R 8  and R 9  are similarly gauged and arranged to give an output of [ - (V + 8V) sin a]. Since any manoeuvre of the ship will take time the course line prediction is suitably delayed by closing switch MN 2  so introducing a change in the initial starting point of the course line dependent on potentiometer P 8 . A similar arrangement for use with a North up P.P.I. display is shown in Fig. 4 (not shown), the means for investigating the result of a change of course and speed being modified, and potentiometer P 2  being arranged to represent the true speed of the response ship. The true speed of the own ship is also used.