Method and system for characterizing an array antenna using near-field measurements

• US 9,331,751 B2
• Filed: 08/05/2014
• Issued: 05/03/2016
• Est. Priority Date: 08/05/2014
• Status: Active Grant

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Sikina, Thomas V., Schuss, Jack J., Hilliard, Joseph E. Jr.
• Primary Examiner(s): Milord, Marceau
• Application Number:
  US14/451,466
• Publication Number:
  US 20160043778A1
• Time in Patent Office: 637 Days
• Field of Search: 455/41.1, 455/67.12, 455/67.11, 455/226.1, 455/115.1, 455/115.2
• US Class Current: 1/1
• CPC Class Codes: G01D 18/00 Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices
• CPC Class Codes: H04B 17/0085 using test signal generators
• CPC Class Codes: H04B 17/21 for calibration; for correcting measurements
• CPC Class Codes: H04B 5/73 for taking measurements, e.g. using sensing coils
• CPC Class Codes: H04B 7/0865 Independent weighting, i.e. weights based on own antenna reception parameters
• CPC Class Codes: H04W 52/383 power control in peer-to-peer links

Abstract

Described embodiments calibrate an array antenna using near-field antenna measurements individually for each antenna element in an antenna under test (AUT). A signal is received at a first AUT antenna element from an antenna probe assembly by transmitting from the antenna probe assembly at each of multiple known probe locations in a near-field of the AUT. A signal is received at each probe location by transmitting from the first antenna element of the AUT to the antenna probe assembly. The received signals are combined into a combined signal for the first antenna element that de-correlates multi-path in the combination result. The combined signal is processed to generate a calibration coefficient for the first AUT antenna element. Remote boundary condition (RBC) testing is performed to reduce temporal instability. The multiple known probe locations lie on one of the following: a planar surface, a cylindrical surface, and a spherical surface.

Claims

1. A method for calibrating an array antenna using near-field antenna measurements, the method comprising:

for a first antenna element in an antenna under test (AUT);

obtaining a received signal at the first AUT antenna element from an antenna probe assembly comprising multiple probe elements, by transmitting from the antenna probe assembly at each of multiple known probe locations in a near-field of the AUT;

obtaining a received signal at each the multiple known probe locations by transmitting from the first AUT antenna element to the antenna probe assembly at each of the multiple known probe locations;

combining the received signals to generate a combined signal for the first antenna element, wherein combining the received signals includes combining the signal in a manner that de-correlates multi-path in the combination result;

processing the combined signal to generate a calibration coefficient for the first AUT antenna element; and

performing remote boundary condition (RBC) testing to reduce or eliminate temporal instability in the calibration test equipment used during the array calibration to isolate temporal instability within the AUT, wherein performing RBC testing includes inserting first, second and third boundary conditions, one at a time, at a specific point in the calibration test equipment and performing corresponding measurements to establish a phase reference,

wherein the multiple known probe locations associated with the first AUT antenna element lie on one of the following;

a plane for planar near-field metrology, a cylindrical surface for cylindrical near-field metrology, and a spherical surface for spherical near-field metrology.

2. The method of claim 1, wherein:

obtaining a received signal for each of multiple known probe locations in a near-field of the AUT includes obtaining a measurement of a received signal; and

combining the received signals to generate a combined signal for the first antenna element includes combining measurements of received signals in a virtual manner to generate a combined measurement.

3. The method of claim 1, further comprising:

repeating obtaining, combining, and processing for other AUT antenna elements to generate calibration coefficients for the other AUT antenna elements.

4. The method of claim 1, wherein:

obtaining, combining, and processing are performed for a first calibration frequency within an operational bandwidth of the AUT; and

the method further comprises repeating obtaining, combining, and processing for the first AUT antenna element for other calibration frequencies across an operational bandwidth of the AUT.

5. The method of claim 1, wherein:

obtaining, combining, and processing are performed for a first polarization state associated with the first AUT antenna element; and

the method further comprises repeating obtaining, combining, and processing for at least one other polarization state associated with the first AUT antenna element.

6. The method of claim 1, wherein:

obtaining a received signal for each of multiple known probe locations in a near-field of the AUT includes transmitting test signals toward the AUT from the multiple known probe locations at different times and receiving a signal at the first AUT antenna element for each of the transmitted test signals.

7. The method of claim 6, wherein:

transmitting test signals toward the AUT from multiple known probe locations includes transmitting test signals from a single probe element that is moved between the multiple known probe locations to form a virtual probe array.

8. The method of claim 6, wherein:

transmitting test signals toward the AUT from multiple known probe locations includes transmitting test signals from multiple probe elements within a probe array in the near-field of the AUT, each of the multiple probe elements being positioned at a corresponding one of the multiple known probe locations, wherein the test signals are transmitted from the multiple probe elements within the probe array one probe element at a time.

9. The method of claim 6, wherein:

transmitting test signals toward the AUT from multiple known probe locations includes transmitting the test signals from one or more probe elements associated with an antenna probe assembly in the near-field, wherein the antenna probe assembly is capable of movement within the near-field of the AUT.

10. The method of claim 9, wherein:

the antenna probe assembly includes multiple probe elements arranged in fixed relation to one another; and

the method further comprises moving the multiple probe elements of the antenna probe assembly as a group to a new location in the near-field of the AUT before transmitting test signals to each new antenna element of the AUT that is tested.

11. The method of claim 9, wherein:

the antenna probe assembly includes a single probe element; and

the method further comprises moving the single probe element of the antenna probe assembly to multiple different locations to generate a virtual probe array for each antenna element of the AUT that is tested.

12. The method of claim 1, wherein:

combining the received signals to generate a combined received signal for the first antenna element includes applying complex weights to the received signals so that the signals align substantially in-phase at the first AUT antenna element.

13. The method of claim 1, wherein:

the multiple known probe locations associated with the first AUT antenna element are arranged in a probe array with any of multiple possible separation distances and lattices as needed in order to produce virtual scanned near-field beams at the AUT elements.

14. The method of claim 1, wherein:

the multiple known probe locations associated with the first AUT antenna element are achieved using an antenna probe assembly having a single or multiple probe elements that can be displaced to specific locations in three-dimensional cardinal space.

15. The method of claim 1, wherein:

combining the received signals to generate a combined received signal includes combining the received signals in a fixed hardware beamformer.

16. A system for characterizing an array antenna using near-field measurements, comprising:

a mount to hold an antenna under test (AUT) during testing;

an antenna probe assembly proximate to the mount, the antenna probe assembly being configured to hold one or more probe elements in known locations within a near-field of an AUT in the mount, wherein the antenna probe assembly is capable of controlled movement within the near-field of the AUT;

at least one radio frequency (RF) signal source to provide test signals for transmission between the antenna probe assembly and the AUT during testing; and

a controller coupled to the AUT, the antenna probe assembly, and the at least one RF signal source to perform near-field metrology for the AUT, wherein the controller is configured to;

cause one or more test signals to be transmitted between a first AUT antenna element and multiple known probe locations associated with the probe assembly;

acquire measurements for the first AUT antenna element resulting from the one or more test signals, the measurements including one measurement for each of the multiple known probe locations;

combine the measurements to generate a combined measurement for the first AUT antenna element, wherein the measurements are combined in a manner that decorrelates multipath signals in the combination result;

use the combined measurement to achieve a near-field metrology result for the AUT; and

perform remote boundary condition (RC) testing to reduce or eliminate temporal instability in the calibration test equipment used during the array calibration to isolate temporal instability within the AUT, wherein performing RBC testing includes inserting, first, second and third boundary conditions, one at a time, at a specific point in the calibration test equipment and performing corresponding measurements to establish a phase reference,

wherein the multiple known probe locations associated with the first AUT antenna element lie on one of the following;

a plane for planar near-field metrology, a cylindrical surface for cylindrical near-field metrology, and a spherical surface for spherical near-field metrology.

17. The system of claim 16, wherein:

the controller is configured to cause test signals to be transmitted from the multiple known probe locations to the first AUT antenna element one at a time; and

the controller is configured to acquire measurements of resulting received signals at the first AUT antenna element.

18. The system of claim 16, wherein:

the controller is configured to cause the one or more test signals to be transmitted from the first AUT antenna element to the multiple known probe locations; and

the controller is configured to acquire measurements of resulting received signals at the multiple known probe locations.

19. The system of claim 16, wherein:

the controller is configured to cause one or more test signals to be transmitted, acquire measurements, and combine the measurements for some or all of the AUT antenna elements, wherein a different set of probe locations is used for each AUT antenna element tested.

20. The system of claim 19, wherein:

the antenna probe assembly includes a probe array including multiple probe elements held in fixed relation to one another; and

the controller is configured to move the multiple probe elements of the antenna probe assembly as a group to different positions for use with different AUT antenna elements.

21. The system of claim 19, wherein:

the antenna probe assembly includes a single probe element; and

the controller is configured to move the single probe element between different locations for each AUT antenna element tested.

22. The system of claim 16, wherein:

the antenna probe assembly is configured to provide movement of the one or more probe elements within one of the following;

a plane in the near-field of the AUT, a cylinder in the near-field of the AUT, and a sphere in the near-field of the AUT.

23. The system of claim 16, wherein:

the controller is configured to combine measurements associated with the first AUT antenna element by applying complex weights to the measurements so that the measurements align substantially in-phase at the first AUT antenna element and summing the weighted measurements.

24. The system of claim 23, wherein:

the controller is configured to dynamically adjust the number of probe locations and the complex weighting factors used to combine the measurements in a manner that minimizes the total scattered error vector magnitude for the multiple AUT antenna elements.

25. The system of claim 16, wherein:

the controller is configured to perform far field pattern calculation for the AUT using near-field metrology.

26. The system of claim 16, wherein:

the controller is configured to calibrate the AUT using near-field metrology.

27. The system of claim 16, wherein:

the AUT includes multiple parallel receive channels and the controller is configured to command some or all of the receive channels to receive in parallel to increase a number of receive AUT elements that can be processed from each probe position and reduce overall data acquisition time.

28. The system of claim 16, wherein:

the probe assembly has multiple parallel receive channels and the controller is configured to command some or all of the receive channels to receive in parallel to reduce overall data acquisition time at each probe position.

29. A method for performing near-field antenna metrology, the method comprising:

for a first antenna element in an antenna under test (AUT);

obtaining a measurement for each of multiple known probe locations in a near-field of the AUT;

combining the measurements to generate a combined measurement for the first antenna element, wherein combining the measurements includes combining the measurements in a manner that de-correlates multi-path signals in the combination result;

performing remote boundary condition (RBC) testing to reduce or eliminate temporal instability in the calibration test equipment used during the array calibration to isolate temporal instability within the AUT, wherein performing RBC testing includes inserting first, second and third boundary conditions, one at a time, at a specific point in the calibration test equipment and performing corresponding measurements to establish a phase reference; and

using the combined measurement to achieve a near-field metrology result for the AUT,

wherein the multiple known probe locations associated with the first AUT antenna element lie on one of the following;

a plane for planar near-field metrology, a cylindrical surface for cylindrical near-field metrology and a spherical surface for spherical near-field metrology.