Selectable doppler filter for radar systems

Claim 2

A filter arrangement for radar systems, said filter arrangement comprising: first filtering means for providing a first predetermined frequency response; second filtering means for providing a second predetermined frequency response, said second response being different than said first response; first means for detecting when a plurality of radar echoes from a specific spatial location have a mean doppler shift substantially equal to zero; second means for detecting when the radar echoes have an amplitude greater than a first predetermined value; means for selecting said second filtering means only if said first detecting means determines that said radar echoes have a mean doppler shift substantially equal to zero and said second detecting means determines that said radar echoes have an amplitude greater than said first predetermined value; wherein the first and second filtering means each comprises a bank of filters having similar passbands and wherein the first detecting means includes means for sensing the outputs of said first or second filtering means; and wherein the means for sensing the filtering means outputs compares the echo signal from zero filters to the peak echo signal from non-zero filters, and provides an indication of detection when zero filter echo signal exceeds the non-zero filter peak echo signal by a second predetermined value.

Claim 3

The filter arrangement of claim 1 wherein the rejection bands of the first and second filtering means are different.

Claim 4

The filter arrangement of claim 2 wherein the rejection bands of the two filtering means are such that the first filtering means provides better rain clutter rejection than the second filtering means, and the second filtering means provides better ground clutter rejection than the first filtering means.

Claim 5

The filter arrangement of claim 1 further comprising means for changing said first and second predetermined value upon selection of the second filtering means to provide a hysteresis effect upon the selection of the first filter.

Claim 6

The filter arrangement of claim 1 including means for delaying the operation of the first detecting means for one coherent processing interval.

Claim 7

The filter arrangement of claim 5 including means for making the filter selection dependent upon data in two adjacent coherent processing intervals.

Claim 8

The filter arrangement of claim 1 wherein the selecting means includes means for selecting the second filter only after analyzing outputs from the first and second detecting means over a plurality of range samples.

Claim 9

The filter arrangement of claim 1 wherein the means for selecting the second filtering means includes UP-DOWN counting means for making it necessary to have more than one output from the first and second detecting means before the second filtering means is selected.

Claim 10

The filter arrangement of claim 1 wherein the means for selecting the second filtering means includes means for changing the filter weights used by a digital processor.

Claim 11

The filter arrangement of claim 1 wherein the first and second filtering means have pass bands suitable for use as the first set of non-zero doppler filters in a doppler radar system.

Claim 12

A filter arrangement for radar systems, said filter arrangement comprising: first filtering means for providing a first predetermined frequency response; second filtering means for providing a second predetermined frequency response, said second response being different than said first response; first means for detecting when a plurality of radar echoes from a specific spatial location have a mean doppler shift substantially equal to zero; second means for detecting when the radar echoes have an amplitude greater than a first predetermined value; means for selecting said second filtering means only if said first detecting means determines that said radar echoes have a means doppler shift substantially equal to zero and said second detecting means determines that said radar echoes have an amplitude greater than said first predetermined value; wherein the second detecting means includes means for using the data contained in a clutter map; and wherein the means for using the data in the clutter map includes means for combining the data from three adjacent coherent processing interval cells to provide a single output data value.

Claim 13

A filter arrangement for radar systems, said filter arrangement comprising: first filtering means for providing a first predetermined frequency response; second filtering means for providing a second predetermined frequency response, said second response being different than said first response; first means for detecting when a plurality of radar echoes from a specific spatial location have a mean doppler shift substantially equal to zero; second means for detecting when the radar echoes have an amplitude greater than a first predetermined value; means for selecting said second filtering means only if said first detecting means determines that said radar echoes have a means doppler shift substantially equal to zero and said second detecting means determines that said radar echoes have an amplitude greater than said first predetermined value; wherein the second detecting means includes means for using the data contained in a clutter map; and wherein the means for using the data in the clutter map includes means for combining the data from three adjacent coherent processing interval cells to provide a single output data value.

Claim 14

The filter arrangement of claim 11 wherein the combining means produces an output data value which is equal to the peak amplitude of the data from the three adjacent coherent processing interval cells.

Claim 15

A filter arrangement for radar systems having a plurality of zero and non-zero doppler filters, said filter arrangement comprising: an adjustable non-zero doppler filter defined by first and second weight sets, said first weight set defining a first filter response which has better rain clutter rejection than a second filter response defined by said second weight set, and said second weight set providing the second filter response with better ground clutter rejection than said first filter response defined by the first weight set; means for determining the peak amplitude of all non-zero doppler filter responses; means for detecting the peak amplitude of all zero doppler filter responses; means for providing a first output when the peak amplitude of the zero doppler filter responses exceeds the peak amplitude of the non-zero doppler filter responses by a first predetermined ratio value; means for providing a second output equal to said first output delayed for one coherent processing interval; means for combining at least three values of azimuth data from a clutter map, said combining means providing a third output when the combined azimuth data values exceed a second predetermined value; means for providing a fourth output when said second and third outputs are present; and means for changing from said first weight set to said second weight set when said fourth output is present.

Claim 16

A filter arrangement for radar systems having a plurality of zero and non-zero doppler filters, said filter arrangement comprising: an adjustable non-zero doppler filter defined by first and second weight sets, said first weight set defining a first filter response which has better rain clutter rejection than a second filter response defined by said second weight set, and said second weight set providing the second filter response with better ground clutter rejection than said first filter response defined by the first weight set; means for determining the peak amplitude of all non-zero doppler filter responses; means for detecting the peak amplitude of all zero doppler filter responses; means for providing a first output when the peak amplitude of the zero doppler filter responses exceeds the peak amplitude of the non-zero doppler filter responses by a first predetermined ratio value; means for providing a second output equal to said first output delayed for one coherent processing interval; means for combining at least three values of azimuth data from a clutter map, said combining means providing a third output when the combined azimuth data values exceed a second predetermined value; means for providing a fourth output when said second and third outputs are present; and means for changing from said first weight set to said second weight set when said fourth output is present.

Claim 17

The filter arrangement of claim 13 including means for changing the first predetermined ratio value when the second filter weight set is selected.

Claim 18

The filter arrangement of claim 13 including means for changing the second predetermined value when the second filter weight set is selected.

Claim 19

The filter arrangement of claim 13 wherein the combining means combines the three azimuth data values to yield a resultant value equal to the peak amplitude of the largest of the three separate azimuth data values.

Claim 20

The filter arrangement of claim 13 wherein the fourth output is provided only after the second and third outputs are present for a plurality of range samples.

Claim 23

The method of claim 18, wherein said selecting step is based on a combination of mean doppler shift and amplitude data from adjacent spatial locations.