Patent GB-653484-A (GB)
Title: Two-coordinate radar system
IPC: G01S1/02
Filed: 1948-09-22
Abstract: 653,484. Radiolocation. DEHN, S. G. (Gilfillan Bros., Inc.). Sept. 22, 1948, No. 24828. [Class 40 (vii)] In a radar system, such as a ground controlled aircraft landing system, in which two antennas severally scan in two co-ordinates and are each adjustable in the scanning co-ordinate of the other, electronic means are provided for indicating on the cathode-ray tube display the condition of adjustment of the other antenna. In Fig. 2 the cathode-ray tube indicating the range and elevation angle of an aircraft S<SP>1</SP> observed by a first antenna scanning in elevation displays in addition two dotted lines V1<SP>1</SP>, V21 representing the limits of the angular field in elevation covered by the beam of a second antenna scanning in azimuth. In a similar manner the azimuth display, Fig. 1 (not shown), indicates the limits of the angular field in azimuth covered by the elevation antenna. As an alternative, a single line may be employed to indicate the axis of an antenna beam. Fig. 3 shows the circuit associated with the elevation display, a similar circuit being provided for the azimuth display. An angle coupling voltage generator 27 is linked with the scanning mechanism of the elevation antenna 9c and produces a D.C. potential varying in accordance with the scanning angle. This potential is applied to sweep amplifier 8 and modifies the amplitude of the deflection currents applied to coils 10d so that successive sweeps of the cathode-ray beam, from the origin O<SP>1</SP> are in accordance with the scan angle of the antenna. To produce the dashed lines V1<SP>1</SP>, V2<SP>1</SP> two potentials which vary in accordance with the angular adjustment of the azimuth antenna in elevation are derived by a pair of potentiometers 11, 12 having their arms carried by a shaft 17 positioned by the elevation adjustment control 18 of the azimuth antenna 9a. A constant difference between the two potentials is produced by setting the arms at different angles or by adjustment of potentiometers 13, 14, 15 and 16, the potential difference determining the angle of separation of the lines V1<SP>1</SP> and V2<SP>1</SP>. The two potentials are applied through cathode followers V1 (A) and V1 (B) to the cathodes of tubes V2 and V4 when they are compared with the angle coupling voltage which is applied to the grids of both tubes. As the angle coupling voltage varies from a high to a low value in one direction of scan, the anode-cathode potentials of tubes V2 and V4 increase and at a first critical voltage dependent on the potential from potentiometer 11, a gas tube V3 connected across tube V2 strikes, causing a negative pulse to be applied through condenser 28 to multivibrator V6. The multivibrator triggers from a stable to an unstable state and produces a positive pulse on lead 35. This positive pulse triggers a normally cut-off oscillator V7 (A), the oscillations arising in the circuit 40, 41 being applied in turn to a cathode-follower V7 (B) which selects only the positive peaks, a tube V8 where the peaks are superposed on the sweep intensifying pulse and grid 10g of the cathode-ray tube. The timeconstant of the multivibrator is made just greater than the time of one sweep of the cathode-ray beam so there appears on the screen a single series of dashes forming the first of the lines V1<SP>1</SP>, V2<SP>1</SP>. In a similar manner, at a second critical voltage, dependent on the potential from potentiometer 12, gas tube V5 across tube V4 strikes and triggers multivibrator stage V6 to produce the second of the dashed lines. During the reverse scan of the antenna when the angle coupling voltage varies from a low to a high value, the potentials across tubes V2 and V4 progressively decrease, resulting in the extinction of gas tubes V3 and V5, and the transmission of positive pulses to multivibrator stage V6. The pulses are however ineffective since the multivibrator has reverted to its stable state. The lines V1<SP>1</SP> and V2' are formed accordingly only when the antenna scans in one direction.