Nearfield calibration method used for phased array antennas containing tunable phase shifters

• US 20030038747A1
• Filed: 08/19/2002
• Published: 02/27/2003
• Est. Priority Date: 08/23/2001
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Paratek Microwave Incorporated (Blackberry Limited)
• Inventors: Patel, Jaynesh, du Toit, Cornelis Frederik, Karasack, Vincent G.
• Granted Patent: US 6,771,216 B2
• Time in Patent Office: Days
• US Class Current: 342/368
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices

Abstract

A method for calibrating a phased array antenna and the calibrated phased array antenna are described herein. In the preferred embodiment of the present invention, the method for calibrating a phased array antenna containing a plurality of electronically tunable phase shifters each of which is coupled to a column of radiating elements includes the steps of: (a) characterizing each of the electronically tunable phase shifters; (b) calculating phase offsets for each column of radiating elements using a nearfield antenna range and the characterized data for each of the electronically tunable phase shifters; and (c) using the calculated phase offsets in a calibration table to adjust the tuning voltage of each of the electronically tunable phase shifters to cause the columns of radiating elements to yield a uniform beam.

Claims

1. A method for calibrating a phased array antenna containing a plurality of electronically tunable phase shifters each of which is coupled to a column of radiating elements, said method comprising the steps of:

characterizing each of the electronically tunable phase shifters;

calculating phase offsets for each column of radiating elements using a nearfield antenna range and the characterized data for each of the electronically tunable phase shifters; and

using the calculated phase offsets in a calibration table to adjust the tuning voltage of each of the electronically tunable phase shifters to cause the columns of radiating elements to yield a uniform beam.

2. The method of claim 1, wherein said characterizing step includes the steps of:

measuring S-parameters for each of the phase shifters while varying the tuning voltage applied to each of the phase shifters in discrete steps across a tuning range;

generating phase-voltage equations for each of the phase shifters based on the measured S-parameters; and

entering the phase-voltage equations into the controller.

3. The method of claim 2, wherein said step of generating phase-voltage equations for each of the phase shifters comprises the steps of:

plotting phase versus the applied tuning voltage; and

determining a best-fit line.

4. The method of claim 1, wherein said calculating step includes:

mounting said phased array antenna in the nearfield antenna range including a scanner probe positioned orthogonal to the phased array antenna in both azimuth and elevation directions.

5. The method of claim 4, wherein said scanner probe is positioned a distance in the range of 0.25λ

to 0.50λ

from an aperture of the phased array antenna, where λ

is a wavelength of a signal to be processed by the antenna.

6. The method of claim 1, further comprising the steps of:

performing a nearfield scan;

producing a azimuth phase hologram plot;

comparing the azimuth phase hologram plot with a desired azimuth phase hologram plot; and

adjusting the calibration table if the azimuth phase hologram plot differs from the desired azimuth phase hologram plot.

7. The method of claim 6, further comprising the steps of:

performing a farfield scan;

producing a farfield plot;

comparing the farfield plot with a desired farfield plot; and

repeating said characterizing step and said calculating step if the farfield plot differs from the desired farfield plot.

8. A method for calibrating a phased array antenna containing a plurality of electronically tunable phase shifters each of which is coupled to a column of radiating elements and a controller for supplying a tuning voltage to the electronically tunable phase shifters, said method comprising the steps of:

applying zero voltage to each of the phase shifters and measuring the phase of each of the plurality of columns of radiating elements in the phased array antenna;

using the measured phase to determine a phase target value for each of the plurality of columns of radiating elements in the phased array antenna;

adjusting a phase shift for each column of radiating elements in the phased array antenna to a value within a predetermined range of the phase target value to generate phase offset data; and

using the phase offset data to produce a calibration table for use in the controller to adjust the tuning voltage of each of the phase shifters to cause the columns of radiating elements to yield a uniform beam.

9. The method of claim 8, further comprising the steps of:

measuring S-parameters for each of the phase shifters while varying a tuning voltage applied to each of the phase shifter in discrete steps across a tuning range;

generating phase-voltage equations for each of the phase shifters based on the measured S-parameters; and

entering the phase-voltage equations into an antenna control algorithm.

10. The method of claim 9, wherein the step of generating phase-voltage equations for each of the phase shifters comprises the steps of:

plotting phase versus the applied tuning voltage; and

determining a best-fit line.

11. The method of claim 10, wherein the best fit line is a third order polynomial.

12. The method of claim 8, further comprising the step of:

positioning a scanner probe orthogonal to the phased array antenna in both azimuth and elevation directions.

13. The method of claim 12, wherein said scanner probe is positioned a distance in the range of 0.25λ

to 0.50λ

from an aperture of the phased array antenna, where λ

is a wavelength of a signal to be processed by the phased array antenna.

14. The method of claim 12, wherein said scanner probe is positioned directly above the center of the column of radiating elements to be tested.

15. The method of claim 8, wherein said step of adjusting the phase shift for each column of radiating elements comprises the step of:

measuring the phase offset of each of the phase shifters and adjusting the phase offset until a desired phase is measured.

16. The method of claim 15, wherein said step of measuring the phase offset of each of the phase shifters comprises the step of:

making a microwave holography measurement to fine-tune the phase values so that a flat phase front is realized in a nearfield antenna measurement.

17. The method of claim 15, wherein said step of measuring the phase offset of each of the phase shifters comprises the step of:

back transforming nearfield scan data to obtain phase values at the aperture of the antenna.

18. The method of claim 8, further comprising the steps of:

making a farfield antenna measurement and calculating a farfield plot; and

comparing the farfield plot to a desired farfield plot.

19. A phased array antenna containing a plurality of electronically tunable phase shifters each of which is coupled to a column of radiating elements and a controller for supplying a tuning voltage to the electronically tunable phase shifters, said phased array antenna is calibrated by a method including the steps of:

applying zero voltage to each of the phase shifters and measuring the phase of each of the plurality of columns of radiating elements in the phased array antenna;

using the measured phase to determine a phase target value for each of the plurality of columns of radiating elements in the phased array antenna;

adjusting a phase shift for each column of radiating elements in the phased array antenna to a value within a predetermined range of the phase target value to generate phase offset data; and

using the phase offset data to produce a calibration table for use in the controller to adjust the tuning voltage of each of the phase shifters to cause the columns of radiating elements to yield a uniform beam.

20. The phased array antenna of claim 19, wherein said calibration method further comprises the steps of:

measuring S-parameters for each of the phase shifters while varying a tuning voltage applied to each of the phase shifter in discrete steps across a tuning range;

generating phase-voltage equations for each of the phase shifters based on the measured S-parameters; and

entering the phase-voltage equations into an antenna control algorithm.

21. The phased array antenna of claim 20, wherein said step of generating phase-voltage equations for each of the phase shifters comprises the steps of:

plotting phase versus the applied tuning voltage; and

determining a best-fit line.

22. The phased array antenna of claim 21, wherein said best fit line is a third order polynomial.

23. The phased array antenna of claim 19, wherein said calibration method further comprises the step of:

positioning a scanner probe orthogonal to the phased array antenna in both azimuth and elevation directions.

24. The phased array antenna of claim 23, wherein said scanner probe is positioned a distance in the range of 0.25λ

to 0.50λ

from an aperture of the phased array antenna, where λ

is a wavelength of a signal to be processed by the phased array antenna.

25. The phased array antenna of claim 23, wherein said scanner probe is positioned directly above the center of the column of radiating elements to be tested.

26. The phased array antenna of claim 19, wherein said step of adjusting the phase shift for each column of radiating elements comprises the step of:

measuring the phase offset of each of the phase shifters and adjusting the phase offset until a desired phase is measured.

27. The phased array antenna of claim 26, wherein said step of measuring the phase offset of each of the phase shifters comprises the step of:

making a microwave holography measurement to fine-tune the phase values so that a flat phase front is realized in a nearfield antenna measurement.

28. The phased array antenna of claim 26, wherein said step of measuring the phase offset of each of the phase shifters comprises the step of:

back transforming nearfield scan data to obtain phase values at the aperture of the antenna.

29. The phased array antenna of claim 19, further comprising the steps of:

making a final farfield antenna measurement and calculating a farfield plot; and

comparing the farfield plot to a desired farfield plot.