Moving target radar

DETAILED DESCRIPTION The prior art as taught by the Kalmus articles includes a mechanically operating correlator which may be an eddy-current drag disc or relatively movable coils operating on a bimorph piezoelectric strip.
This invention arises from the realization that the microphonics are introduced by the mechanically operating components.
In accordance with this invention a moving target radar is provided which is fully electronic and has no moving parts.
The incoming signal reflected from an object in the protected region is converted into I and Q signals.
Each signal is transmitted through a variable bandpass filter whose pass band is controlled by the magnitude at the output of the filter.
As the output of the filter increases the pass band is reduced by increasing the cut-off frequency at the low-frequency end of the pass band.
This mode of controlling the pass band is based on the realization that the clutter, typically produced by growth moving in the wind, is of low doppler frequency while an intruder moving into the protected region moves at a substantially higher rate than the growth and produces a signal of substantially higher doppler frequency than the clutter.
Reduction of the pass band at the low-frequency end as the clutter increases thus achieves an increase in signal-plus-noise-to-noise ratio without appreciable loss in sensitivity to the presence of intruders.
The I and Q signals at the outputs of the filters are each converted into quadrature signals which may be designated as I3 and I4 and Q3 and Q4 respectively.
The cross products 13Q4 and 14Q3 are then derived.
The difference between 13Q4 and 14Q3 is derived and serves to indicate the presence of an intruder, if any.
This difference is passed through a low-pass filter and to the intruder indicators.
The effect of this is essentially to suppress the clutter because the growth moves backward and forward in the wind, and it appears in the processing in both products as equal magnitudes and is eliminated during subtraction steps