System and method for microwave imaging with suppressed sidelobes using a sparse antenna array

• US 7,280,068 B2
• Filed: 07/14/2005
• Issued: 10/09/2007
• Est. Priority Date: 07/14/2005
• Status: Active Grant

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Baharav, Izhak, Taber, Robert C., Lee, Gregory Steven
• Primary Examiner(s): Sotomayor; John B
• Application Number:
  US11/181,111
• Publication Number:
  US 20070013575A1
• Time in Patent Office: 817 Days
• Field of Search: 342/22, 342/27, 342/52, 342/54, 342/179, 342/180
• US Class Current: 342/22
• CPC Class Codes: G01S 13/89 for mapping or imaging
• 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

A microwave imaging system suppresses sidelobes in a microwave image captured using a sparse antenna array using an illumination system that operates in two different illumination modes. The antenna array including subarrays of antenna elements arranged in a sparse geometry to form complementary subarray patterns. The illumination system operates in a first mode to transmit microwave illumination to both of the complementary subarray patterns of the antenna array and receive reflected microwave illumination from both of the complementary subarray patterns of the antenna array to produce a first receive signal. The illumination system further operates in a second mode to transmit microwave illumination to a first one of the complementary subarray patterns of the antenna array and receive reflected microwave illumination from a second one of the complementary subarray patterns of the antenna array to produce a second receive signal. Sidelobes are suppressed using a linear combination of the first and second receive signals.

Claims

1. An illumination system within a microwave imaging system for illuminating an antenna array including antenna elements for directing microwave illumination to and from a target to capture a microwave image of said target, said antenna array including subarrays of said antenna elements arranged in a sparse geometry to form complementary subarray patterns of said antenna array, said illumination system comprising:

a transmitter operable to transmit microwave illumination towards said antenna array;

a receiver operable to receive from said antenna array reflected microwave illumination reflected from said target; and

an illumination network operable in a first mode to transmit said microwave illumination from said transmitter to both of said complementary patterns of said antenna array and provide said reflected microwave illumination from both of said complementary subarray patterns of said antenna array to said receiver, wherein said illumination network is further operable in a second mode to transmit said microwave illumination from said transmitter to a first one of said complementary subarray patterns of said antenna array and provide said reflected microwave illumination from a second one of said complementary subarray patterns of said antenna array to said receiver.

2. The illumination system of claim 1, wherein said illumination network includes at least two microwave horns for illuminating said complementary subarray patterns of said antenna array.

3. The illumination system of claim 2, wherein said illumination network further includes a respective phase plate for each of said at least two microwave horns, and wherein said respective phase plates are operable to generate complementary illumination patterns to illuminate said complementary patterns of said antenna array.

4. The illumination system of claim 3, wherein said illumination network includes a first microwave horn operably connected to a first phase plate to generate a first illumination pattern for illuminating said first complementary subarray pattern of said antenna array, a second microwave horn operably connected to a second phase plate to generate a second illumination pattern for illuminating said second complementary subarray pattern of said antenna array and a third microwave horn operably connected to a third phase plate to generate a third illumination pattern for illuminating both said complementary subarray patterns of said antenna array.

5. The illumination system of claim 4, wherein said illumination network further includes a circulator connected to said third horn, a first switch connected to said receiver and arranged to selectively connect to said circulator in said first mode and said first horn in said second mode and a second switch connected to said transmitter and arranged to selectively connect to said circulator in said first mode and said second horn in said second mode.

6. The illumination system of claim 3, wherein said illumination network includes a first microwave horn operably connected to a fixed phase plate to generate a first illumination pattern for illuminating said first complementary subarray pattern of said antenna array and a second microwave horn operably connected to a variable phase plate to generate a second illumination pattern for illuminating said second complementary subarray pattern of said antenna array and a third illumination pattern for illuminating both said complementary subarray patterns of said antenna array.

7. The illumination system of claim 6, wherein said illumination network further includes a circulator connected between said receiver and said second horn and switch connected to said transmitter and arranged to selectively connect to said circulator in said first mode and said second horn in said second mode.

8. The illumination system of claim 3, wherein said illumination network includes a first microwave horn operably connected to a first phase plate to generate a first illumination pattern for illuminating said first complementary subarray pattern of said antenna array and a second microwave horn operably connected to a second phase plate to generate a second illumination pattern for illuminating said second complementary subarray pattern of said antenna array.

9. The illumination system of claim 8, wherein said illumination network further includes a power splitter connected to a circulator, a first switch connected to said receiver and arranged to selectively connect to said circulator in said first mode and said first horn in said second mode, a second switch connected to said transmitter and arranged to selectively connect to said circulator in said first mode and said second horn in said second mode, a third switch connected to said first horn and arranged to selectively connect to said power splitter in said first mode and said receiver in said second mode and a fourth switch connected to said second horn and arranged to selectively connect to said power splitter in said first mode and said transmitter in said second mode.

10. The illumination system of claim 8, wherein said illumination network further includes a 90-degree hybrid coupler, a first switch connected to said receiver and arranged to selectively connect to said 90-degree hybrid coupler in said first mode and said first horn in said second mode, a second switch connected to said transmitter and arranged to selectively connect to said 90-degree hybrid coupler in said first mode and said second horn in said second mode, a third switch connected to said first horn and arranged to selectively connect to said 90-degree hybrid coupler in said first mode and said receiver in said second mode and a fourth switch connected to said second horn and arranged to selectively connect to said 90-degree hybrid coupler in said first mode and said transmitter in said second mode.

11. The illumination system of claim 8, wherein said illumination network further includes a first circulator connected to said first horn, a second circulator connected to said second horn, a power splitter connected to said first circulator, said second circulator and a third circulator, a first switch connected to said receiver and arranged to selectively connect to said third circulator in said first mode and said first circulator in said second mode and a second switch connected to said transmitter and arranged to selectively connect to said third circulator in said first mode and said second circulator in said second mode.

12. The illumination system of claim 8, wherein said illumination network further includes a first circulator connected to said first horn, a second circulator connected to said second horn, a 90-degree hybrid coupler connected to said first circulator and said second circulator, a first switch connected to said receiver and arranged to selectively connect to said 90-degree hybrid coupler in said first mode and said first circulator in said second mode and a second switch connected to said transmitter and arranged to selectively connect to said 90-degree hybrid coupler in said first mode and said second circulator in said second mode.

13. The illumination system of claim 8, wherein said receiver includes a first receiver and a second receiver, and wherein said illumination network further includes a first circulator connected to said first horn and said first receiver, a second circulator connected to said second horn and said second receiver, a power splitter connected to said first circulator, a first switch connected to said transmitter and arranged to selectively connect to said power splitter in said first mode and said second circulator in said second mode and a second switch connected to said second circulator and arranged to selectively connect to said power splitter in said first mode and said transmitter in said second mode.

14. The illumination system of claim 8, wherein said receiver includes a first receiver and a second receiver, wherein said transmitter includes a first transmitter and a second transmitter phase-locked with respect to one another, and wherein said illumination network further includes a first circulator connected to said first horn, said first receiver and said first transmitter and a second circulator connected to said second horn, said second receiver and said second transmitter.

15. The illumination system of claim 8, wherein said illumination network further includes a circulator connected to said transmitter, a variable gain amplifier connected to said circulator, a summation node connected to said variable gain amplifier and said receiver and a 90-degree hybrid coupler connected to said first horn, said second horn, said summation node and said circulator.

16. The illumination system of claim 1, wherein said illumination network includes first illumination optics and second illumination optics, and wherein said transmitter and said receiver form a first transceiver operably connected to said first illumination optics, and further comprising:

a second transceiver operably connected to said second illumination optics.

17. A microwave imaging system, comprising:

an antenna array including a plurality of antenna elements, each of said antenna elements being capable of being programmed with a respective direction coefficient to direct microwave illumination to and from a target associated with an object, said antenna array including subarrays of said antenna elements arranged in a sparse geometry to form complementary subarray patterns of said antenna array;

an illumination system operable to provide microwave illumination to illuminate said complementary patterns of said antenna array and receive reflected microwave illumination reflected by said target from said complementary subarray patterns of said antenna array to produce a first receive signal in a first mode and a second receive signal in a second mode; and

a processor operable to determine a value associated with the target in a microwave image of the object as a linear combination of said first receive signal and said second receive signal.

18. The system of claim 17, wherein said illumination system is operable to illuminate both said complementary subarray patterns of said antenna array and receive reflected microwave illumination reflected by said target from both said complementary subarray patterns of said antenna array to produce said first receive signal, and wherein said illumination system is further operable to provide said microwave illumination to illuminate a first one of said complementary subarray patterns of said antenna array and receive said reflected microwave illumination from a second one of said complementary subarray patterns of said antenna array to produce said second receive signal.

19. The system of claim 17, wherein each of said antenna elements in said complementary subarray patterns is programmed with a respective first direction coefficient to direct microwave illumination from said target toward said illumination system in said first mode and each of said antenna elements in one of said complementary subarray patterns is programmed with a respective second direction coefficient inverted with respect to said respective first direction coefficient in said second mode.

20. The system of claim 17, wherein said complementary subarray patterns form one of a cross-shaped subarray pattern or a picture frame subarray pattern.

21. The system of claim 17, wherein said processor is further operable to switch between said first mode and said second mode.

22. The system of claim 17, wherein said processor is further operable to substantially simultaneously receive said first receive signal and said second receive signal.

23. The system of claim 22, wherein said illumination system includes a first receiver connected to receive said reflected microwave illumination to produce said second receive signal in said second mode and to produce a first portion of said first receive signal in said first mode, wherein said illumination system further includes a second receiver connected to receive said reflected microwave illumination to produce a second portion of said first receive signal in said first mode, and wherein said processor is further operable to perform digital multiplication and addition of said first portion of said first receive signal, said second portion of said first receive signal and said second receive signal to determine said value.

24. The system of claim 17, wherein said first receive signal and said second receive signal are complex signals describing a main scanning lobe and one or more sidelobes and said processor is further operable to add the product of said first receive signal and a first complex multiplier with the product of said second receive signal and a second complex multiplier to constructively enhance said main scanning lobe and destructively cancel said one or more sidelobes, and wherein said first complex multiplier and said second complex multiplier are selected as a function of said sparse geometry.

25. The system of claim 17, further comprising:

a display for displaying the microwave image of the object.

26. A method for capturing a microwave image of an object, comprising:

providing an antenna array including a plurality of antenna elements for directing microwave illumination to and from a target associated with said object, said antenna array including subarrays of said antenna elements arranged in a sparse geometry to form complementary subarray patterns of said antenna array;

illuminating both said complementary subarray patterns of said antenna array to direct a first transmit beam of said microwave illumination towards said target;

receiving a first reflect beam of reflected microwave illumination reflected by said target from both said complementary subarray patterns of said antenna array to produce a first receive signal in a first mode;

illuminating a first one of said complementary subarray patterns of said antenna array to direct a second transmit beam of said microwave illumination towards said target;

receiving a second reflect bean of said reflected microwave illumination from a second one of said complementary subarray patterns of said antenna array to produce a second receive signal in a second mode; and

determining an intensity of said reflected microwave illumination reflected from said target as a linear combination of said first receive signal and said second receive signal.

27. The method of claim 26, wherein said receiving said first receive signal and said receiving said second receive signal are performed substantially simultaneously.

28. The method of claim 26, wherein said first receive signal and said second receive signal are complex signals describing a main scanning lobe and one or more sidelobes, and wherein said measuring further comprises:

adding the product of said first receive signal and a first complex multiplier with the product of said second receive signal and a second complex multiplier to constructively enhance said main scanning lobe and destructively cancel said one or more sidelobes.