Method and apparatus to minimize antenna backside signal response and ambiguity

• US 20100066608A1
• Filed: 08/06/2009
• Published: 03/18/2010
• Est. Priority Date: 09/17/2008
• Status: Active Grant

• Current Assignee: United States Air Force (Government of the United States of America)
• Original Assignee: United States Air Force (Government of the United States of America)
• Inventors: Paschen, Dean, Pratt, Frank, McCarthy, Daniel, Eichel, Lary
• Granted Patent: US 8,013,792 B2
• Time in Patent Office: Days
• US Class Current: 342/378
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: G01S 7/2813 Means providing a modification of the radiation pattern for cancelling noise, clutter or interfering signals, e.g. side lobe suppression, side lobe blanking, null-steering arrays specially adapted to secondary radar systems G01S13/762; aerials or aerials systems H01Q21/29, H01Q25/00

Abstract

Method and apparatus for minimizing antenna backside signal response and ambiguity in low frequency applications, particularly low frequency synthetic aperture radar (SAR). Various time delay elements are selectably switched into the signal path so as to cause a null to be placed in the antenna response pattern in the direction of undesired radar returns. The means for selectably switching may be dithered so as to introduce modulation onto the undesired radar return to aid in the discrimination and removal of the undesired radar return from the SAR image during post processing.

Claims

1. In an antenna having at least two elements, an apparatus for minimizing antenna:

backside signal response and ambiguity, comprising;

a means for causing a phase difference having a plurality of outputs;

a signal path connecting each of said at least two elements to a corresponding output of said means for causing a phase difference;

a means for causing a variable time delay disposed in at least one said signal path;

a processor; and

a software program;

said software program comprising computer implementable instructions capable of being executed in said processor wherein, when executed, causes said processor to control said means for causing a variable time delay so as to

cause a null to be positioned in the antenna pattern of said antenna in the direction of an undesired received signal; and

dither the position of said null.

2. The apparatus of claim 1, wherein said means for causing a phase difference comprises at least one pair of outputs having a 180 degree relative phase difference.

3. The apparatus of claim 1, wherein said means for causing a variable time delay further comprises an individually selectable plurality of radio frequency transmission media of various electrical length, each of said plurality having a first end and a second end.

4. The apparatus of claim 3, wherein said means for causing a variable time delay further comprises a first switch placed at said first end of said plurality of radio frequency transmission media and a second switch placed at said second end of said plurality of radio frequency transmission media so as to cause said signal path to route through a selected said radio frequency transmission media.

5. The apparatus of claim 1, wherein said processor in cooperation with said software program further comprises means to

detect signal amplitude variations in said signal path;

quantize said signal amplitude variations;

correlate said quantized signal amplitude variations with dithering of the position of said null; and

discriminate signals in said signal path as being ambiguous or non-ambiguous on the basis of said correlation.

6. The apparatus of claim 4, wherein said processor cooperates with a means for detecting signal amplitude in said at least one signal path.

7. A method for minimizing antenna backside signal response and ambiguity, comprising the steps of:

introducing a relative phase difference between signal paths each supplying signals to at least two antenna elements of an antenna;

causing a variable time delay in at least one said signal path;

executing computer implementable software steps that control said variable time delay so as to

cause a null to be positioned in the antenna pattern of said antenna in the direction of an undesired received signal; and

dither the position of said null.

8. The method of claim 7, wherein said step of introducing a relative phase difference further comprises introducing a 180 degree phase difference.

9. The method of claim 7, wherein said step of causing a variable time delay further comprises the step of selecting a time delay from a plurality of discrete selectable time delay elements.

10. The method of claim 9, wherein said discrete selectable time delay elements are radio frequency transmission media of various electrical length, each having a first end and a second end.

11. The method of claim 10, wherein said step of selecting further comprises electrically switching said first end and said second end of any of said frequency transmission media into said at least one signal path.

12. The method of claim 7, wherein said step of executing computer implementable software steps further comprises executing software steps so as to

detect signal amplitude variations in said signal path;

quantize said signal amplitude variations;

correlate said quantized signal amplitude variations with dithering of the position of said null; and

discriminate signals in said signal path as being ambiguous or non-ambiguous on the basis of said correlation.