Adaptive clutter filtering to improve high sub-clutter visibility radar detection performance
AssigneeBAE Systems Information and Electronic Systems Integration Inc.
InventorsGregory S. Laste, Garret E. Murdza
Life of this patent
Estimating the term…
Abstract
In an aircraft-mounted Doppler radar clutter rejection system, a flexible, sharp band pass filter uses Taylor weighting, an FFT and a module for selecting which of the Doppler cells are to be activated, thus to control the band pass characteristic and set the clutter line to the speed of the aircraft.
Claims18
In an aircraft-mounted active radar for detecting incoming threats, a method for adaptively setting the clutter line of a filter used to reject clutter to correspond to the Doppler shift associated with sensed aircraft ground speed, comprising the steps of:
- analog-to-digitally converting radar pulses received at the aircraft from a surveilled area;
- range gating the returned pulses;
- multiplying a predetermined number of pulses from a range gate with weights;
- applying the pulse weights to a fast Fourier transform to generate side-by-side Doppler cells;
- and,
- selecting those Doppler cells for activation having Doppler shift frequencies above a clutter line Doppler shift frequency associated with the sensed aircraft ground speed, thereby to reject clutter having Doppler shifts below the aircraft ground speed and for passing returns having Doppler shift frequencies above the aircraft ground speed, whereby the clutter rejection line is set in accordance with the sensed aircraft ground speed.
A method for eliminating the use of fixed analog filters to filter out ground clutter in an active radar system mounted on a moving platform to detect the presence of incoming threats closing in on the platform in which the clutter line for the filter is determined by the maximum speed of the platform, comprising:
- converting radar returns at the moving platform from analog to digital form;
- weighting the converted returns with weights that when processed with a fast Fourier transform establish a large main lobe region and uniform monotonic side lobes below a predetermined rejection level;
- coupling the weighted returns to the fast Fourier transform for creating side-by-side Doppler cells;
- and,
- selecting for target detection only those Doppler cells having Doppler shift frequencies above the clutter line which are above the Doppler shift associated with the ground speed of the moving platform, whereby the resulting clutter filter Doppler clutter line frequency is the same as the Doppler frequency associated with the sensed speed of the platform.
Apparatus for the rejection of ground clutter in an active radar system mounted aboard a moving platform that projects pulses towards the ground and that is designed to detect an incoming threat, comprising:
- an antenna for receiving pulsed radar returns at said platform;
- a heterodyning unit for heterodyning the pulses received at said antenna for the down-conversion thereof;
- a low pass filter coupled to the output of said heterodyning unit;
- an analog-to-digital converter coupled to the output of said low pass filter;
- a weight generator for multiplying the analog-to-digital-converted signals with weights;
- a fast Fourier transform module coupled to said weight generator for forming Doppler cells;
- and,
- a Doppler cell selector for selecting Doppler cells corresponding to clutter line Doppler shifts above the Doppler shift associated with the ground speed of said platform, whereby the output of said fast Fourier transform module is filtered by a band pass filter characteristic having a lower edge adaptively movable to correspond to the Doppler shift associated with the ground speed of said platform through said selection of Doppler cells.
In an active Doppler radar system carried aboard a moving platform, a band pass filter for filtering out ground clutter having a band pass characteristic with variable edges, comprising:
- a weight generator for weighting Doppler returns at said platform;
- a fast Fourier transform module coupled to the output of said weight generator for generating contiguous Doppler cells;
- and,
- a Doppler cell selector module for selecting contiguous Doppler cells to form the pass band of said band pass filter, with the selection of Doppler cells defining the band pass edges of said band pass filter, one of said band pass filter edges being a clutter line defined by the Doppler associated with the speed of the moving platform.
Dependencies are inferred from the claim text.