MTI system and method

An airborne moving target indicator comprising:

• an airborne radar platform;
• a radar system carried by said platform including a transmitter, receiver, transmit-receiver switch, digital automatic gain control circuit, and an indicator;
• means for modifying the doppler frequencies of the output signal of said radar receiver in response to movement of said radar platform;
• means for tracking relative to the side lobes the main beam detected targets having sufficient reflective power to overcome side lobe attenuation;
• means responsive to said tracking means for calculating the doppler of targets detected in the side lobes after said modification of the doppler frequencies;
• a plurality of doppler filters interconnected between said receiver and said indicator;
• means responsive to said calculating means for inhibiting less than all of the doppler filters.

A method of separating the return signals from moving targets from the return signals from stationary target in a doppler radar system comprising the steps of:

• a. transmitting a succession of radar pulses separated by an interpulse period;
• b. detecting the return signal from each of the transmitted radar pulses;
• c. dividing the interpulse period into a plurality of discrete range bins;
• d. sampling the amplitude of the return signal from each of the succession of transmitted radar pulses in each of the discrete range bins;
• e. varying the amplification of the return signal in each of the plurality of discrete range bins from each of the transmitted radar pulses in response to the sampled amplitude in the corresponding one of the plurality of discrete range bins of the return signal from a preceding one of the transmitted radar pulses, the variation in amplification of the return signal in each of the plurality of discrete range bins being independent of the amplification in the others of the plurality of discrete range bins of the same return signal to thereby reduce the amplitude variations in the radar return signal;
• f. detecting discrete targets in the main beam of the radar system having sufficient reflective power to generate false alarms through entry into the radar system through a side lobe;
• g. tracking the discrete targets relative to a side lobe;
• h. calculating the doppler frequency of the discrete targets when in the side lobes;
• i. processing the amplified return signals on the basis of the phase shift between successive return signals from the same target to separate moving targets from stationary targets;
• and,
• j. inhibiting less than all of the doppler filters responsively to the doppler frequency calculation at the range of the side lobe target when the detected discrete target is in the side lobe of the radar system to thereby reduce false alarms.

A radar system comprising:

• means for transmitting a succession of radar pulses separated by an interpulse period;
• means including an amplifier for receiving a return signal from each of said transmitted radar pulses;
• means for sampling the amplitude of the return signal from each of the transmitted radar pulses in a plurality of range bins during the interpulse period;
• and,
• means for varying the gain of said amplifier for the return signal from one of said transmitted radar pulses in each of said plurality of range bins in response to the sampled amplitude in the corresponding range bin of the return signal from a prior one of said transmitted radar pulses.

A radar system comprising:

• means for transmitting a succession of radar pulses separated by an interpulse period;
• means for receiving and amplifying a return signal from each of said transmitted radar pulses;
• means for sampling the amplitude of the amplified return signal from each of said transmitted radar pulses during a plurality of range bins in the interpulse period;
• and,
• means for varying the degree of amplification of the return signal in each of said plurality of range bins in response to the sampled amplitude of the return signal from a prior one of said transmitted radar pulses in the corresponding range bin, the degree of amplification of the return signal from each of said transmitted radar pulses in each of said plurality of range bins being independent of the amplification of the return signal in any other of said plurality of range bins.

A doppler radar system comprising:

• means for transmitting a succession of radar pulses separated by substantially equal interpulse periods;
• means for amplifying the return signal from each of said transmitted radar pulses;
• a return signal processor for processing the amplified return signal from each of said transmitted radar pulses;
• means for establishing a signal level related to the amplitude of the return signal from each of said transmitted radar pulses in a plurality of range bins during the interpulse periods;
• and
• means responsive to said established signal levels for adjusting the gain of said amplifying means for each of said plurality of range bins independently of the gain of said amplifying means for the others of said plurality of range bins.

A system for automatically controlling the amplitude of the return signals applied to the return signal processor of a doppler radar system comprising:

• a source of the return signal from each of a succession of radar pulses;
• a processor for return signals;
• and
• circuit means for applying said return signals from said source to said processor, said circuit means including:
• an amplifier,
• means for detecting the amplitude of the radar return signal in each of a plurality of discrete range bins, and
• means connected to said return signal amplitude detecting means for generating a digital control signal for each of said discrete range bins in response to the detected amplitude of the return signals in the corresponding range bins from a plurality of preceding radar pulses.
• the gain of said amplifier for each of said plurality of discrete range bins being responsive to said digital control signals independently of the gain of said amplifier for each of the other of said plurality of discrete range bins to thereby provide independent control of the amplification of the return signal from each radar pulse in each of said plurality of discrete range bins.

A method of separating the return signals from moving targets from the return signals from stationary target in a doppler radar system comprising the steps of:

• a. transmitting a succession of radar pulses separated by an interpulse period;
• b. detecting the return signal from each of the transmitted radar pulses;
• c. dividing the interpulse period into a plurality of discrete range bins;
• d. sampling the amplitude of the return signal from each of the succession of transmitted radar pulses in each of the discrete range bins;
• e. varying the amplification of the return signals in each of the plurality of discrete range bins from each of the transmitted radar pulses in response to the sampled amplitude in the corresponding one of the plurality of discrete range bins of the return signal from a preceding one of the transmitted radar pulses, the variation in amplification of the return signal in each of the plurality of discrete range bins being independent of the amplification in the others of the plurality of discrete range bins of the same return signal to thereby reduce the amplitude variations in the radar return signal;
• and,
• f. processing the amplified return signals on the basis of the phase shift between successive return signals from the same target to separate moving targets from stationary targets.

A method of varying the amplification of the return signal from a radar pulse comprising the steps of:

• a. transmitting a first radar pulse;
• b. detecting the return signal from the first radar pulse;
• c. periodically sampling the amplitude of the detected return signal from the first radar pulse;
• d. converting said sampled amplitude signal into a digital gain control signal;
• e. storing the digital gain control signal;
• f. transmitting a second radar pulse;
• g. detecting the return signal from the second radar pulse;
• and,
• h. selectively varying the amplification of the detected return signal from the second radar pulse responsively to each of the stored gain control signals derived from the return signal from the first radar pulse.

A method of varying the amplification of the return signal from a succession of radar pulses comprising the steps of:

• a. dividing the time interval between successive radar pulses into a plurality of range bins;
• b. sampling the amplitude of the return signal from each radar pulse in each of the range bins;
• and,
• c. varying the amplification in each range bin of the return signal from one radar pulse independently of the amplification of the return signal in the other range bins in response to the sampled amplitude of the corresponding range bin of the return signal from a preceding radar pulse.

Apparatus comprising:

• means for transmitting a succession of radar pulses separated by an interpulse period;
• means including an amplifier for receiving a return signal from each of said transmitted radar pulses;
• means for sampling the amplitude of the return signal from each of the transmitted radar pulses in a plurality of range bins during the interpulse period;
• means for varying the gain of said amplifier for the return signal from one of said transmitted radar pulses in each of said plurality of range bins in response to the sampled amplitude in the corresponding range bin of the return signal from a prior one of said transmitted radar pulses;
• and,
• means for storing the up-dated gain control signal for controlling the gain of said amplifier for the next radar return signal.

A method of separating the return signals from moving targets from the return signals from stationary target in a doppler radar system comprising the steps of:

• a. transmitting a succession of radar pulses separated by an interpulse period;
• b. detecting the return signal from each of the transmitted radar pulses;
• c. dividing the interpulse period into a plurality of discrete range bins;
• d. sampling the amplitude of the return signal from each of the succession of transmitted radar pulses in each of the discrete range bins;
• e. varying the amplification of the return signal in each of the plurality of discrete range bins from each of the transmitted radar pulses in response to the sampled amplitude in the corresponding one of the plurality of discrete range bins of the return signal from a preceding one of the transmitted radar pulses, the variation in amplification of the return signal in each of the plurality of discrete range bins being independent of the amplification in the others of the plurality of discrete range bins of the same return signal to thereby reduce the amplitude variations in the radar return signal;
• f. processing the amplified return signals on the basis of the phase shift between successive return signals from the same target to separate moving targets from stationary targets;
• and,
• g. recording to stationary targets.

In an AEW MTI having a radar system, means for removing the effects of radar platform movement from the main beam targets, a bank of doppler filters and an indicator, the improvement comprising:

• means for tracking targets detected in the main beam and having sufficient reflective power to override side lobe attenuation;
• means for calculating the residual doppler frequency of said targets resulting from side lobe rather than main beam detection;
• and
• means responsive to said calculating means for inhibiting selected ones of the doppler filters corresponding to the calculated doppler frequency for the range of said targets.

A method of reducing overland false alarms in an AEW system having a radar system, an array of doppler filters and an indicator comprising the steps of:

• a. detecting discrete targets in the main beam of the radar system having sufficient reflective power to generate false alarms through entry into the radar system through a side lobe;
• b. tracking the discrete targets relative to the side lobe;
• c. modifying the doppler frequencies of the discrete targets responsively to radar system platform movement;
• d. calculating the residual doppler frequency of the targets when in the side lobes;
• and
• e. inhibiting less than all of the doppler filters responsively to the calculation at the range of the side lobe target to thereby reduce false alarms.

A method reducing the interference of ground clutter in a doppler radar system comprising the steps of:

• a. detecting the main lobe radar signal and the ground clutter entering the system through a side lobe of the antenna;
• b. splitting the detected ground clutter into a plurality of doppler channels;
• c. computing the ground doppler;
• and,
• d. tuning the clutter rejection circuits responsively to the computed ground doppler so that target echoes do not have to compete with side lobe clutter.

Apparatus for reducing the interference of ground clutter in a doppler radar system comprising:

• means for detecting the main lobe radar signal and the ground clutter entering the system through a side lobe of the antenna;
• means for splitting the detected ground clutter into a plurality of doppler channels;
• means for computing the ground doppler;
• and,
• means for tuning the clutter rejection circuits responsively to the computed ground doppler so that target echoes do not have to compete with side lobe clutter.

A system for automatically controlling the amplitude of signals applied to a radar signal processor comprising:

• a source of successive radar return signals;
• a radar signal processor;
• amplifier means connected between said source and said processor for amplifying said radar signals and for applying said amplified radar signals to said processor;
• detector means for detecting the amplitude of said radar signals;
• and
• gain control means responsive to said detector means for selectively adjusting the gain of said amplifier means, said gain adjusting means being independently adjustable for each of a plurality of discrete time intervals related to each of said radar signals whereby the gain of said amplifier means is independently adjustable for each time interval of one of said radar signals responsively to the detected amplitude of a related time interval of the preceding one of said radar signals.

A moving target indicator comprising:

• a radar platform;
• a radar system carried by said platform including a transmitter, receiver, transmit-receive switch, and an indicator;
• means for modifying the doppler frequencies of the output signal of said radar receiver in response to movement of said radar platform;
• means for tracking relative to the side lobes the main beam detected targets having sufficient reflective power to overcome side lobe attenuation;
• means responsive to said tracking means for calculating the doppler of targets detected in the side lobes after said modification of the doppler frequencies;
• a plurality of doppler filters interconnected between said receiver and said indicator;
• and
• means responsive to said calculating means for inhibiting less than all of the doppler filters.