Adaptive digital automatic gain control for mti radar systems

Claim 2

In a radar system having a moving target filter and a data processing system apparatus for reducing the input dynamic range requirements of said filter and said data processing system by maintaining received signal clutter at a predetermined low voltage level comprising: a receiver in said system adapted to receive electromagnetic energy and produce in response thereto a video signal with a gain factor controlled by an automatic gain control signal; and means responsive to said video signal and said moving target filter output signal for generating said automatic gain control signal as a function of clutter level in said video signal and residual clutter level in said moving target filter output signal; means for generating an autoMatic gain control signal as a function of noise level in said video signal; and means for summing said automatic gain control signals.

Claim 3

In a radar system having a moving target indicator filter with a given filter formation period, apparatus for reducing the input dynamic range requirements thereof by maintaining clutter in the input video signal and output moving target indicator signal of said filter substantially constant at a predetermined level comprising: a receiver in said system adapted to receive electromagnetic energy and produce in response thereto a video signal with a gain factor controlled by an automatic gain control signal; means for dividing said video signal of each range sweep of said radar system into range elements; first comparing means for continually comparing said video input signal with a first reference voltage level to obtain a binary-1 signal when said video input signal exceeds said first reference voltage, and a binary-0 signal when said video input signal does not exceed said first reference voltage; second comparing means for periodically comparing said moving target indicator output signal with a second reference voltage level to obtain a binary-1 signal if said moving target indicator output signal exceeds said second reference voltage level, and a binary-0 signal if said moving target indicator output signal does not exceed said second reference voltage; integrating means for producing said automatic gain control signal for each successive range element of a given sweep by incrementing a stored value for a given range element during a range sweep if either said first or second comparing means produces a binary-1 signal and decrementing said stored value for said given range element if neither said first or second comparing means produces a binary-1 signal; means for cyclically reading out said automatic gain control signal during each successive range sweep with range element values thereof synchronized with corresponding range elements; and coupling means for applying said automatic gain control signal read out to said receiver.

Claim 4

In a radar system having a moving target indicator filter with a given filter formation period, apparatus for reducing the input dynamic range requirements thereof by maintaining clutter in the input video signal and output moving target indicator signal of said filter substantially constant at a predetermined level comprising: a receiver in said system adapted to receive electromagnetic energy and produce in response thereto a video signal with a gain factor controlled by an automatic gain control signal; means for dividing said video signal of each range sweep of said radar system into range elements; first comparing means for continually comparing said video input signal with a first reference voltage level to obtain a binary-1 signal when said video input signal exceeds said first reference voltage, and a binary-0 signal when said video input signal does not exceed said first reference voltage; second comparing means for periodically comparing said moving target indicator output signal with a second reference voltage level to obtain a binary-1 signal if said moving target indicator output signal exceeds said second reference voltage level, and a binary-0 signal if said moving target indicator output signal does not exceed said second reference voltage; integrating means for producing said automatic gain control signal for each successive range element of a given sweep by incrementing a stored value for a given range element during a range sweep if either said first or second comparing means produces a binary-1 signal and decrementing said stored value for said given range element if neither said first or second comparing means produces a binary-1 signal; means for cyclically reading out said automatic gain control signal during each successive range sweep with range element values thereof synchronized with corresponding range elements; and coupling means for applying said automatic gain control signal read out to said receiver.

Claim 5

Apparatus as defined in claim 8 wherein said coupling means includes a low-pass filter means for smoothing out changes in said automatic gain control signal between range elements.

Claim 6

Apparatus as defined in claim 3 wherein said filter has a time constant approximately equal to several range element periods.

Claim 7

Apparatus as defined in claim 4 including: third sampling means or sampling the voltage level of said video input signal after the last range sweep for every radar azimuth scan to obtain a signal noise sample; third comparing means for comparing each signal noise sample with a third reference voltage level to obtain a binary-1 output signal if said signal noise sample exceeds said third reference voltage, and a binary-0 output signal if said signal noise sample does not exceed said third reference voltage; integrating means for developing a noise level control signal by incrementing or decrementing a stored value according to whether said output signal is a binary 1 or a binary 0 once during each azimuth scan; and means for adding said noise level control signal to the output of said filter, whereby said automatic gain control signal is provided with a noise component about which a clutter component varies.

Claim 8

In a radar system having a data processing system, apparatus for reducing the input dynamic range requirements of said data processing system by maintaining received video signal clutter at a predetermined voltage level comprising: a receiver in said system adapted to receive electromagnetic energy and produce in response thereto a video signal with a gain factor controlled by an automatic gain control signal; means for dividing said video signal of each range sweep of said radar system into range elements; means coupling said automatic gain control signal to said receiver for smoothing out changes iN said automatic gain control signal between range elements including means for computing a running average of said automatic gain control signal over a predetermined number of range elements; means for sampling the voltage level of said video signal for each range element; means for comparing each sample with a predetermined voltage level to obtain a difference value; means for continuously accumulating said difference values; means for producing said automatic gain control signal for each successive range element of a given sweep proportional to the arithmetic sum of all integrated difference values of corresponding range elements of previous range sweeps; a shift register for delaying difference values a number of range element periods equal to said predetermined number of range elements; means for continuously subtracting delayed difference values at the output of said shift register from values in said accumulating means; and means for dividing the output of said accumulating means by said predetermined number to produce said automatic gain control signal for control of said gain factor of said receiver.

Claim 9

In a radar system having a data processing system, apparatus for reducing the input dynamic range requirements of said data processing system by maintaining received video signal clutter at a predetermined voltage level comprising: a receiver in said system adapted to receive electromagnetic energy and produce in response thereto a video signal with a gain factor controlled by an automatic gain control signal; means for dividing said video signal of each range sweep of said radar system into range elements; means coupling said automatic gain control signal to said receiver for smoothing out changes iN said automatic gain control signal between range elements including means for computing a running average of said automatic gain control signal over a predetermined number of range elements; means for sampling the voltage level of said video signal for each range element; means for comparing each sample with a predetermined voltage level to obtain a difference value; means for continuously accumulating said difference values; means for producing said automatic gain control signal for each successive range element of a given sweep proportional to the arithmetic sum of all integrated difference values of corresponding range elements of previous range sweeps; a shift register for delaying difference values a number of range element periods equal to said predetermined number of range elements; means for continuously subtracting delayed difference values at the output of said shift register from values in said accumulating means; and means for dividing the output of said accumulating means by said predetermined number to produce said automatic gain control signal for control of said gain factor of said receiver.

Claim 10

In a radar system, apparatus for reducing the input dynamic range requirements thereof by maintaining received signal clutter at a predetermined voltage level comprising: a receiver in said system adapted to receive electromagnetic energy and produce in response thereto a video signal with a gain actor controlled by an automatic gain control signal; means for generating said automatic gain control signal as a function of deviation of the clutter level in said video signal from said predetermined voltage level; means for dividing said video signal of each range sweep of said radar system into range elements; comparing means for comparing the video signal amplitude of each range element with a predetermined voltage level to obtain a digital difference signal, and including an analog-to-digital converter wherein each difference signal comprises a binary number greater than 1; means for continuously adding said difference signals from corresponding range elements of following range sweeps; integrating means including an adder and shift registers adapted to recirculate sums from said adder for addition of subsequent difference signals; means for producing said automatic gain control signal for each successive range element of a given sweep proportional to the sum of digital difference signals of corresponding range element of previous range sweeps, comprising a digital-to-analog converter; and an analog filter coupling said automatic gain control signal to said receiver and having a time constant approximately equal to several range element periods.

Claim 11

In a radar system, apparatus for reducing the input dynamic range requirements thereof by maintaining received signal clutter at a predetermined voltage level comprising: a receiver in said system adapted to receive electromagnetic energy and produce in response thereto a video signal with a gain actor controlled by an automatic gain control signal; means for generating said automatic gain control signal as a function of deviation of the clutter level in said video signal from said predetermined voltage level; means for dividing said video signal of each range sweep of said radar system into range elements; comparing means for comparing the video signal amplitude of each range element with a predetermined voltage level to obtain a digital difference signal, and including an analog-to-digital converter wherein each difference signal comprises a binary number greater than 1; means for continuously adding said difference signals from corresponding range elements of following range sweeps; integrating means including an adder and shift registers adapted to recirculate sums from said adder for addition of subsequent difference signals; means for producing said automatic gain control signal for each successive range element of a given sweep proportional to the sum of digital difference signals of corresponding range element of previous range sweeps, comprising a digital-to-analog converter; and an analog filter coupling said automatic gain control signal to said receiver and having a time constant approximately equal to several range element periods.

Claim 12

In a radar system having a data processing system, apparatus for reducing the input dynamic range requirements of said data processing system by maintaining received video signal clutter at a predetermined voltage level comprising: a receiver in said system adapted to receive electromagnetic energy and produce in response thereto a video signal with a gain factor controlled by an automatic gain control signal; means for dividing said video signal of each range sweep of said radar system into range elements; means for sampling the voltage level of said video signal for each range element; means for comparing each sample with a predetermined voltage level to obtain a difference value, including an analog-to-digital converter wherein said difference value of each sample greater than said predetermined voltage level is positive, and said difference value of each sample less than said predetermined voltage level is negative; means for continuously adding said difference values from corresponding range elements of following range sweeps; integrating means including an adder and shift registers adapted to recirculate sums from said adder back through said adder for addition of subsequent difference values; means for Producing said automatic gain control signal for each successive range element of a given sweep comprising a digital-to-analog converter, said automatic gain control signal being proportional to the arithmetic sum of all integrated difference values of corresponding range elements of previous range sweeps; and means coupling said automatic gain control signal to said receiver for smoothing out changes in said automatic gain control signal between range elements comprising means for computing a running average of said automatic gain control signal over a predetermined number of range elements.

Claim 13

In a radar system having a data processing system, apparatus for reducing the input dynamic range requirements of said data processing system by maintaining received video signal clutter at a predetermined voltage level comprising: a receiver in said system adapted to receive electromagnetic energy and produce in response thereto a video signal with a gain factor controlled by an automatic gain control signal; means for dividing said video signal of each range sweep of said radar system into range elements; means for sampling the voltage level of said video signal for each range element; means for comparing each sample with a predetermined voltage level to obtain a difference value, including an analog-to-digital converter wherein said difference value of each sample greater than said predetermined voltage level is positive, and said difference value of each sample less than said predetermined voltage level is negative; means for continuously adding said difference values from corresponding range elements of following range sweeps; integrating means including an adder and shift registers adapted to recirculate sums from said adder back through said adder for addition of subsequent difference values; means for Producing said automatic gain control signal for each successive range element of a given sweep comprising a digital-to-analog converter, said automatic gain control signal being proportional to the arithmetic sum of all integrated difference values of corresponding range elements of previous range sweeps; and means coupling said automatic gain control signal to said receiver for smoothing out changes in said automatic gain control signal between range elements comprising means for computing a running average of said automatic gain control signal over a predetermined number of range elements.