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

• US 6,686,873 B2
• Filed: 08/19/2002
• Issued: 02/03/2004
• Est. Priority Date: 08/23/2001
• Status: Expired due to Term

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Paratek Microwave Incorporated (Blackberry Limited)
• Inventors: du Toit, Cornelis Frederick, Karasack, Vincent G., Patel, Jaynesh
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US10/223,576
• Publication Number:
  US 20030038746A1
• Time in Patent Office: 533 Days
• Field of Search: 455/67.1, 455/67.4, 342/165-175, 342/195, 342/359, 342/360-384
• US Class Current: 342/174
• 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, without having any prior phase shift versus tuning voltage data, each of the electronically tunable phase shifters; (b) calculating phase offsets for each column of radiating elements using a farfield 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, without having any prior phase shift versus tuning voltage data, each of the electronically tunable phase shifters, wherein said characterizing step includes the steps of;

(a) setting each of the electronically tunable phase shifters to a random phase;

(b) successively applying a plurality of tuning voltages to a first one of the phase shifters coupled to a first column of radiating elements;

(c) measuring, at a receiver, phase and amplitude of a signal transmitted from the first column of radiating elements for each tuning voltage applied to the first phase shifter;

(d) determining phase shift versus tuning voltage data for the first column of radiating elements; and

repeating steps (b), (c) and (d) for each column of radiating elements after resetting each of the electronically tunable phase shifters to the random phase;

calculating phase offsets for each column of radiating elements using a farfield 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 calculating step includes:

mounting said phased array antenna in the farfield antenna range including a scanner probe positioned far enough away from the phased array antenna such that the scanner probe receives energy emitted form the phased array antenna.

3. The method of claim 1, wherein said using step includes:

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 a phase shifter value in the calibration table if the azimuth phase hologram plot differs from the desired azimuth phase hologram plot.

4. The method of claim 3, 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.

5. A method for calibrating a phased array antenna containing a plurality of electronically tunable phase shifters, said method comprising the steps of:

(a) positioning a receiver away from the phased array antenna such that the receiver receives energy emitted from the phased array antenna;

(b) setting each of the electronically tunable phase shifters in the phased array antenna to a random phase;

(c) successively applying a plurality of tuning voltages to a first one of the electronically tunable phase shifters coupled to a first column of radiating elements in the phased array antenna to control the phase shift provided for the first column of radiating elements;

(d) measuring phase and amplitude of a signal transmitted from the first column of radiating elements in the phased array antenna to the receiver for each tuning voltage applied to the first electronically tunable phase shifter;

(e) determining phase shift versus tuning voltage data for the first column of radiating elements;

(f) repeating steps (c), (d) and (e) for each column of radiating elements after resetting each of the electronically tunable phase shifters to the random phase; and

(g) using the determined phase shift versus tuning voltage data to adjust the phase shift for each of the electronically tunable phase shifters to yield a uniform phase front at an aperture of the phased array antenna.

6. The method of claim 5, wherein the tuning voltages are applied in discrete increments.

7. The method of claim 5, wherein the step of measuring phase and amplitude of a signal transmitted from the first column of radiating elements in the phased array antenna to the receiver for each tuning voltage applied to the first phase shifter comprises the steps of:

converting the measured phase and amplitude to complex numbers;

plotting the complex numbers on a real-imaginary graph.

8. The method of claim 5, wherein the step of determining phase shift versus tuning voltage data for the first column of radiating elements comprises the steps of:

generating voltage-phase equations; and

using the generated equations to construct an antenna boresight calibration table.

9. The method of claim 5, wherein the step of using the determined phase shift versus tuning voltage data to adjust the phase shift for each of the electronically tunable phase shifters to yield a uniform phase front at the aperture of the phased array antenna comprises the steps of:

performing a nearfield scan of the phased array antenna;

producing a azimuth phase hologram plot;

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

adjusting a phase shifter value in a calibration table if the azimuth phase hologram plot differs from the desired azimuth phase hologram plot.

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

performing a farfield scan of the phased array antenna;

producing a farfield plot;

comparing the farfield plot with a desired farfield plot; and

repeating steps (b), (c), (d), (e), (f) and (g) if the farfield plot differs from the desired farfield plot.

11. A phased array antenna containing a plurality of electronically tunable phase shifters each of which is coupled to a column of radiating elements, said phased array antenna is calibrated by performing the following steps:

(a) positioning a receiver away from the phased array antenna such that the receiver receives energy emitted from the phased array antenna;

(b) setting each of the electronically tunable phase shifters in the phased array antenna to a random phase;

(c) successively applying a plurality of tuning voltages to a first one of the electronically tunable phase shifters coupled to a first column of radiating elements in the phased array antenna to control the phase shift provided for the first column of radiating elements;

(d) measuring phase and amplitude of a signal transmitted from the first column of radiating elements in the phased array antenna to the receiver for each tuning voltage applied to the first electronically tunable phase shifter;

(e) determining phase shift versus tuning voltage data for the first column of radiating elements;

(f) repeating steps (c), (d) and (e) for each column of radiating elements after resetting each of the electronically tunable phase shifters to the random phase; and

(g) using the determined phase shift versus tuning voltage data to adjust the phase shift for each of the electronically tunable phase shifters to yield a uniform phase front at an aperture of the phased array antenna.

12. The phased array antenna of claim 11, wherein the tuning voltages are applied in discrete increments.

13. The phased array antenna of claim 11, wherein the step of measuring phase and amplitude of a signal transmitted from the first column of radiating elements in the phased array antenna to the receiver for each tuning voltage applied to the first phase shifter comprises the steps of:

converting the measured phase and amplitude to complex numbers;

plotting the complex numbers on a real-imaginary graph.

14. The phased array antenna of claim 11, wherein the step of determining phase shift versus tuning voltage data for the first column of radiating elements comprises the steps of:

generating voltage-phase equations; and

using the generated equations to construct an antenna boresight calibration table.

15. The phased array antenna of claim 11, wherein the step of using the determined phase shift versus tuning voltage data to adjust the phase shift for each of the electronically tunable phase shifters to yield a uniform phase front at the aperture of the phased array antenna comprises the steps of:

performing a nearfield scan of the phased array antenna;

producing a azimuth phase hologram plot;

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

adjusting a phase shifter value in a calibration table if the azimuth phase hologram plot differs from the desired azimuth phase hologram plot.

16. The phased array antenna of claim 15, further comprising the steps of:

performing a farfield scan of the phased array antenna;

producing a farfield plot;

comparing the farfield plot with a desired farfield plot; and

repeating steps (b), (c), (d), (e), (f) and (g) if the farfield plot differs from the desired farfield plot.

17. The phased array antenna of claim 11, wherein said calibrated phased array antenna is used in a satellite communication system.

18. The phased array antenna of claim 11, wherein said calibrated phased array antenna is used in a microwave terrestrial communication system.

19. The phased array antenna of claim 11, wherein said electronically tunable phase shifters are located in a different plane than the radiating elements.

20. The phased array antenna of claim 11, wherein two adjacent columns of radiating elements are separated from one another by 0.5 to 1 λ

of the signal transmitted by the calibrated phased array antenna.