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US 4,394,658 AGranted
Adaptive MTI clutter tracker-canceller method and apparatus
AssigneeSperry Corporation
InventorRobert D. Short, III
Life of this patent
Estimating the term…
Abstract
An adaptive clutter canceller for adaptively cancelling clutter with non-zero mean Doppler frequencies. Received clutter signals averaged over a predetermined number of range cells and over an azimuth extent. The resulting averaged signal is used to shift the clutter spectrum to a zero mean Doppler and subsequently cancelled.
Claims11
An adaptive MTI clutter canceller comprising:
- mixer means having input means for receiving signals at first and second frequencies, said second frequency differing from said first frequency by a difference frequency, and output means for providing signals, at said output means, having frequencies representative of said difference frequency;
- delay means having input means coupled to said output means of said mixer means for time delaying said signals at said difference frequencies and for providing said time delayed signals at an output means thereof;
- phase comparator means having first input means coupled to said output means of said delay means and second input means coupled to said output means of said mixer means for providing signals at an output means that are representative of phase differences between signals coupled from said output means of said time delay means and said output means of said mixer means;
- first averaging means having input means coupled to said output means of said phase comparator means for providing signals representative of an average, over a first predetermined period, of signals coupled from said phase comparator means;
- second averaging means coupled to receive said average signal from said first averaging means for providing signals representative of an average, over a second predetermined period, of signals coupled from said averaging means;
- and
- means having output means coupled to said input means of said mixer means and input means coupled to receive said average signal from said second averaging means for providing signals having frequencies that are functions of said average signals coupled from said second averaging means.
4 more elements
A method for cancelling doppler shifted clutter comprising the steps of:
- mixing a signal representative of said doppler shifted clutter at a time t, said signal having a representative frequency, with a first signal having a first frequency from a VCO to obtain a signal having a frequency that is determined by differencing said representative frequency and said first frequency;
- delaying said difference frequency signal by a time T to obtain a time delayed signal, T being an elapsed time after said time delay;
- comparing said time delayed signal with a signal representative of said doppler shifted clutter at a time substantially T+t to obtain a signal representative of the phase difference between said time delayed signal and said representative signal at time T+t;
- averaging said phase difference over a first predetermined time interval to obtain a first average signal;
- averaging said first time average signal over a second predetermined time interval to obtain a second time average signal;
- and
- controlling said voltage controlled oscillator with said second time average signal.
4 more elements
Dependencies are inferred from the claim text.