System for processing the signal received by a sideways looking airborne radar system

• US 3,927,405 A
• Filed: 05/17/1973
• Issued: 12/16/1975
• Est. Priority Date: 05/19/1972
• Status: Expired due to Term

• Current Assignee: Henri Poinsard, Jean Lemoing
• Original Assignee: Henri Poinsard, Jean Lemoing
• Inventors: Poinsard, Henri, Lemoing, Jean
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Montone, G. E.
• Application Number:
  US05/361,443
• Time in Patent Office: 943 Days
• Field of Search: 343/5CM,5DP,9,7A,17.2R,17.5
• US Class Current: 342/194
• CPC Class Codes: G01S 13/9011 with frequency domain processing of the SAR signals in azimuth G01S13/9005 takes precedence

Abstract

The present invention relates to a system for processing the signal received by a sideways looking airborne radar system. The received signals are compared with a sawtooth frequency modulated reference signal, the slope and the repetition period of which is a function of the velocity of the aircraft. The compared signals are passed through a digital integrator, the integration time of which is equal to the repetition period of the sawtooth. Control means, receiving the velocity of the aircraft controls the slope and the repetition period of the sawtooth and the integration time.

Claims

1. A system for processing the signals received by a sideways looking airborne pulse radar system, used in combination with a device for measuring the velocity of the aircraft comprising:

first generating means for providing a reference signal;

second generating means for providing a plurality of sawtooth signals each sawtooth signal having a repetition period and a slope dependent on both the velocity of the aircraft and the distance of a determined target region;

a plurality of modulating means for modulating said reference signal respectively with said sawtooth signals, thereby providing sawtooth frequency modulated signals;

distance gating means for successively selecting portions of said sawtooth frequency modulated signals at predetermined instants of each repetition period of the radar pulses;

comparing means for comparing said received signals with the output signal of said distance gating means, providing output signals in response to said comparison;

range-gated integrating filtering means for integrating each output signal of the comparing means during a period equal to the repetition period of the corresponding sawtooth signal used for providing said output signal and control means, fed by said velocity measuring device and coupled to said second generating means, for controlling the periods and slopes of said sawtooth signals and to said integrating means for controlling their integration time.

2. The combination of claim 1, wherein said integrating filtering means comprise a digital integrator having a plurality of distance channels and a data transfer device for delivering integrated signal at the end of each integration period, said integrating filtering means having a plurality of integration times equal to the recurrence period of said sawtooth signals.

3. Integrating filtering means as claimed in claim 2, wherein said digital integrator comprise a shift register.

4. The combination of claim 2, wherein said control means comprise:

computing means receiving the output signal of said velocity measuring device, for computing and controlling said slope and repetition period of said sawtooth signals, clock means supplying pulses at a determined repetition rate, and counting circuits connected to said computing means and said clock means for supplying control signals to said distance gating means and said integrating filtering means.

5. The combination of claim 4, wherein said counting circuits also provide synchro pulses for said radar system.

6. The combination of claim 1, wherein each modulating means comprise:

an input for receiving said reference signal;

an output for delivering a sawtooth frequency modulated signal;

a first and a second mixers, each followed by a filter, and connected in series between said input and said output, a third and a fourth mixers, each followed by a filter, coupled respectively to said first and second mixers;

a first local oscillator connected both to said third and fourth mixers;

a second and a third local oscillators connected respectively to said third and fourth mixers, said oscillators being identical with one another and have their frequencies linearly controllable, being arranged in one and the same statically controlled enclosure and one of them operating at a fixed frequency whilst the other is supplied at its input control with a sawtooth signal.

7. A system for processing the signals received by a sideways looking airborne pulse radar system, used in combination with a device for measuring the velocity of the aircraft comprising:

first generating means for providing a reference signal;

second generating means for providing a plurality of sawtooth signals, each sawtooth signal having a repetition period and a slope depending on both the velocity of the aircraft and the distance of a determined target region;

distance gating means for successively selecting portions of said sawtooth signals at determined instants of each repetition period of the radar pulses;

modulating means for modulating said reference signal with the output signal of said distance gating means thereby providing a sawtooth frequency modulated signal;

comparing means for comparing said received signals with said sawtooth frequency modulated signal, providing output signals in response to said comparison;

range-gated integrating filtering means for integrating each output signal of the comparing means during a period equal to the repetition period of the corresponding sawtooth signal used for providing said output signaL; and

control means fed by said velocity measuring device and coupled to said second generating means for controlling the periods and slopes of said sawtooth signals and to said integrating means for controlling their integration time.