System and method for imaging objects

• US 20100265117A1
• Filed: 04/22/2010
• Published: 10/21/2010
• Est. Priority Date: 10/24/2007
• Status: Active Grant

• Current Assignee: ELTA Systems Limited (Government of Israel)
• Original Assignee: ELTA Systems Limited (Government of Israel)
• Inventors: WEISS, Nathan
• Granted Patent: US 8,319,678 B2
• Time in Patent Office: Days
• US Class Current: 342/22
• CPC Class Codes: G01S 13/003 Bistatic radar systems; Multistatic radar systems
• CPC Class Codes: G01S 13/887 for detection of concealed objects, e.g. contraband or weapons
• CPC Class Codes: G01S 13/9058 Bistatic or multistatic SAR
• CPC Class Codes: G01S 13/9088 Circular SAR [CSAR, C-SAR]

Abstract

An active imaging system for imaging a target is described. The system includes a transmitting unit, a receiving unit, an antenna arrangement coupled to the transmitting unit and/or the receiving unit via a front end unit, and an image processing unit coupled to the receiving unit. The system also includes a control system coupled to the transmitting unit, the receiving unit and/or the image processing unit for controlling operation thereof. The antenna arrangement includes at least one rotating antenna synthetically forming a circular antenna. The image processing unit is configured for creating an image of the object by employing a synthetic aperture radar imaging algorithm.

Claims

1. An active imaging system for imaging a target, the system comprising:

a transmitting unit configured to generate electromagnetic radiation signal in microwave wave frequency range for scanning the target;

a receiving unit configured to receive microwave radiation re-radiated from the target;

an antenna arrangement coupled to said transmitting unit and said receiving unit via a front end unit, and configured for transmitting and receiving electromagnetic radiation signal in the microwave wave frequency range, wherein said antenna arrangement includes a sparse array of unitary antennas operating for receiving and transmitting the electromagnetic radiation and including a plurality of antenna elements forming a synthetic antenna configured for rotating about an axis passing through a phase center of said synthetic antenna and orthogonal to a plane of the sparse array so as to fill in an aperture of said synthetic antenna;

an image processing unit coupled to the receiving unit and preprogrammed by a mathematical model configured for analyzing received electromagnetic radiation signal and creating an image of at least one object located within the target by employing an imaging algorithm which includes synthetic aperture processing; and

a control system coupled to at least one of the following units;

said transmitting unit, said receiving unit and said image processing unit; and

configured for controlling operation thereof.

2. The system of claim 1, wherein said electromagnetic radiation is selected from the frequency range of about 300 MHz to about 1 THz.

3. The system of claim 1, wherein a frequency of rotation of the synthetic antenna is in the range of 1 rev/sec to 30 rev/sec.

4. The system of claim 1, wherein a frequency of rotation of the axis passing through the phase center and orthogonal to the plane of the sparse array around said another axis is in the range of 0.5 rev/sec to 5 rev/sec.

5. The system of claim 1,

wherein the transmitting unit includes:

a variable frequency signal generator coupled to the control system, and configured for generating a reference microwave signal, and

a modulator coupled to the variable frequency generator and to the control system, and configured for modulating said reference microwave signal and producing a modulated signal;

wherein the receiving unit includes;

a detector configured for demodulating a signal reradiated from the target, and

a digital A/D converter coupled to the detector and configured for digitizing the signal produced by the detector;

wherein the front-end unit includes;

a power splitter coupled to the modulator and the antenna arrangement and configured to split the modulated signal into a first portion relayed to the antenna arrangement for transmitting and a second portion; and

a mixer coupled to the detector, to the power splitter, and to the antenna arrangement, and configured for mixing the second portion of the modulated signal with the microwave radiation re-radiated from the target and relaying the mixed signal to the detector.

6. The system of claim 5, wherein the front-end unit includes a power amplifier arranged between the splitter and the antenna arrangement;

and a low noise amplifier arranged between the mixer and the antenna arrangement.

7. The system of claim 1, wherein the mathematical model is capable of discriminating between different objects located within the target, and alerting an operator to potential threats.

8. The system of claim 1, wherein the antenna arrangement comprises a rotating arm including:

an electromagnetic circular waveguide connected to the front-end unit,

a quasi-optical transition element connected to the electromagnetic circular waveguide for providing quasi-optical to electromagnetic waveguide transition,

a quasi-optical waveguide rotary joint, and

a quasi-optical waveguide connected to the quasi-optical waveguide rotary joint at one end of the quasi-optical waveguide;

thereby forming a rotating antenna by allowing the electromagnetic wave to enter or to exit the quasi-optical waveguide directly through an outer end of the quasi-optical waveguide.

9. The system of claim 8, further comprising:

another quasi-optical transition element,

another circular waveguide downstream of said another quasi-optical transition element, and

an antenna element connected to said another circular waveguide.

10. The system of claim 8, wherein the antenna arrangement further comprises a stationary arm comprising:

a stationary antenna;

a quasi-optical waveguide for coupling the stationary antenna to the front end unit; and

an RF electromagnetic waveguide for coupling the stationary antenna to the front end unit.

11. The system of claim 10, wherein the stationary antenna is maintained in the vicinity of the rotating arm, while at a place which is arranged at a distance from the axis of rotation larger than the radius of a circle formed by the rotating antenna.

12. The system of claim 10, wherein the stationary antenna is located ahead of the rotating arm at a predetermined distance from the axis of rotation shorter than the radius of a circle formed by the rotating antenna.

13. The system of claim 1, further comprising a frequency multiplier downstream of the transmitting unit and upstream of the front end unit.

14. The system of claim 13, wherein said transmitting unit, said receiving unit, said control system, and said image processing unit are mounted in a stationary portion of the system, whereas frequency multiplier, the front end unit and the antenna arrangement are mounted in a rotating portion of the system.

15. The system of claim 1, wherein the antenna arrangement includes a plurality of rotating receiving antennas distributed on a disk, and at least one stationary transmitting antenna arranged in the vicinity to the receiving antennas at a distance from the center of rotation of the disk larger than the radius of the disk.

16. The system of claim 15, wherein said plurality of receiving antennas is arranged at different distances from the center of rotation.

17. The system of claim 1, wherein the antenna arrangement includes a plurality of rotating receiving antennas distributed on a disk, and at least one stationary transmitting antenna arranged ahead of the rotating disk at a distance from the axis of rotation shorter than the radius of the disk.

18. The system of claim 1, further comprising a video camera arranged outside the rotation radius of the rotating antenna.

19. A method for imaging a target, comprising:

generating and transmitting an electromagnetic radiation signal in microwave wave frequency range for scanning the target;

collecting microwave radiation re-radiated from the target by employing an antenna arrangement including a sparse array of unitary antennas operating for receiving and transmitting the electromagnetic radiation and including a plurality of antenna elements forming a synthetic antenna configured for rotating about an axis passing through a phase center of said synthetic antenna and orthogonal to a plane of the sparse array; and

creating an image of the target using collected microwave radiation re-radiated from the target by employing an imaging algorithm which includes synthetic aperture processing.

20. The method of claim 19, wherein the target includes at least one object selected from visible objects and objects concealed by a clothing material.