Patent GB-1264145-A (GB)
Inventor: DICKEY FRANK R JR
IPC: G01S13/44
Filed: 1969-02-17
Abstract: 1,264,145. Radar. GENERAL ELECTRIC CO. 17 Feb., 1969, No. 8553/69. Heading H4D. In a simultaneous lobing aerial radar system, sum and difference signals are derived from the echoes received by the component aerials. The relative amplitudes and phases of said signals are adjusted, after which they are algebraically combined by means providing a composite signal having a varied phase centre aerial characteristic. In this way, motion of the radar system may be compensated. As described, a radar system is mounted in an aircraft, which is moving at a velocity V, Fig. 1, and comprises a scanning aerial system, which as shown has reached an angular position # with respect to the aircraft's line of flight. The component velocities parallel to and perpendicular to the aerial system axis are Vcos# and Vsin# respectively. The aerial system comprises two radiators 5, 6, Fig. 2, with respective reflectors 7 connected to a magic-tee junction 4, the system being rotated by a motor 8. A transmitter 1 controlled by a keyer 2 feeds the "sum" port of the junction 4 with pulses at time intervals of T. Echo replies are received at the "sum" and "difference" ports of the junction 4 and are converted to an intermediate frequency by means of mixers 14, 15 and a local oscillator 16. The difference signal (#) is adjusted to an amplitude VT.# by a potentiometer 20, forming part of a resolver circuit 17, and is applied to a rotor winding 18, directly coupled to the motor 8, and revolving in synchronism with the aerial system. A signal (K#) proportional to VTsin# is induced in a rotor winding 19 and is added to the sum signal (#), in phase in an adder 29, and in antiphase in an adder 24. The output (#-K#) from the adder 24 is delayed for time T by a delay line 26 and after amplitude detection is applied to one input of a subtractor 32. The output (#+K#) from the adder 29 is applied after amplitude detection to the other terminal of the subtractor 32. Output from the subtractor 32 is applied through a rectifier 33 to an indicator 34 to display MTI information. In a second embodiment (Fig. 5, not shown), the aerial system comprises a four-horn feed with a common reflector and an elevation drive motor (67) as well as an azimuth drive motor (8). The feed waveguides are connected to a network of magic-tee junctions having a sum output (#), an elevation difference output (j# EL ), and an azimuth difference output (j# AZ ). Two resolvers, coupled to the motor (8), are provided which modulate the amplitudes of the difference signals j# EL , j# AZ  by the factors VTcos#, VTsin#, respectively. The elevation difference signal is further processed in a time varied gain controlled amplifier (83), after which it is added to the azimuth difference signal from the VTsin# resolver, and the resultant signal is combined with the sum signal for eventual display on an indicator (34) as in the first embodiment. The gain of the amplifier (83) is controlled by a voltage derived from an adder having one input from a sine potentiometer (91) and another input from a cosine potentiometer (89), the arms of both potentiometers being coupled to the elevation drive motor (67). The potentiometer (91) has a constant voltage input, and the potentiometer (89) has input from a periodic hyperbolic waveform generator (86), which is controlled by an altitude motor (87) and the radar transmitter keyer (2). An output from the generator (86) controls the ground range sweep circuits of the cathode-ray tube indicator (34). In a third embodiment, a-transmitter keyer 2, Fig. 4, also controls a flip-flop circuit 37 to develop a positive and negative going square wave at half the radar P.R.F. This wave is applied to a balanced modulator 36 which is in circuit with the difference signal (#) derived from the aerial system. The output from the modulator 36 (#) is thus alternately in phase or in antiphase in succeeding pulse repetition periods (T). The signals are applied to another balanced modulator 38 where they are amplitude modulated by the signal VTsin# developed by a sine potentiometer 39, driven from the azimuth scanning motor 8, and a linear potentiometer 40. A relative phase shift of 90 degrees is introduced in the output signals (K#) from the modulator 38 by a circuit 44 and they are combined with the sum (#) signals in an adder 45. The signals are then taken both directly, and through a delay line 51 to inputs of a subtractor 53, which provides output for an indicator 56. Unwanted signals are blanked out by an output from the flip-flop circuit 37, connected by a lead 57. An input from a balanced modulator 59 may also be connected to-the adder 45, by means of a switch 58, said modulator 59 being then fed with the difference signals (#) and with a modulating signal proportional to the angular velocity of the aerial system, which is derived from a direct current generator coupled to the motor 8.