Phased array calibration using sparse arbitrarily spaced rotating electric vectors and a scalar measurement system

• US 6,720,919 B1
• Filed: 09/20/2002
• Issued: 04/13/2004
• Est. Priority Date: 09/20/2002
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Taylor, Don, Sizer, Theodore, Sinsky, Jeffrey H.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US10/247,733
• Publication Number:
  US 20040056799A1
• Time in Patent Office: 571 Days
• Field of Search: 342/368, 342/174, 342/372, 342/377
• US Class Current: 342/368
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices

Abstract

A method, controller, system, and computer program for generating data points by measuring the power of the transmitted/received signal while each antenna element is rotated through a series of phase angles. Thereafter, a pairwise comparison of these data points is performed in order to determine the phase and amplitude corrections needed for each antenna element. This pairwise analysis uses as few as three signal measurements for each antenna element, made at sparse, arbitrarily spaced phase angles. Further, the method includes smart data selection to ignore bad data points resulting from anomalies or noise bursts.

Claims

1. A method of calibrating an antenna element, arbitrarily selected from a plurality of such antenna elements, said antenna elements making up a transmit phased array antenna, said method comprising the steps of:

applying a respective one of a plurality of transmit signals, which each initially has the same defined amplitude and phase, to each of the plurality of antenna elements;

maintaining the phase and amplitude of the one of said transmit signals that is applied to the arbitrarily selected antenna element as it is initially, while rotating the phase of the respective transmit signals applied to each of the plurality of antenna elements other than the transmit signal supplied to the arbitrarily selected antenna element, through a sequence of prescribed phase steps;

at each prescribed phase step of said sequence, combining each of the respective transmit signals from each of said plurality of antenna elements with the transmit signal from the arbitrarily selected antenna element in pairwise fashion to produce a plurality of combined signals; and

determining a phase error and amplitude error for each of the plurality of antenna elements other than the arbitrarily selected antenna element based on the plurality of combined signals.

2. The method of claim 1, wherein the phase of the transmit signal applied to each of the plurality of antenna elements is rotated using a direct digital synthesizer (DDS) corresponding to each of the plurality of antenna elements.

3. The method of claim 2, wherein said determined phase error and amplitude error is used to adjust the phase and amplitude of said DDS corresponding to each of the plurality of antenna elements.

4. The method of claim 1, wherein said combining of transmit signals includes directing a portion the transmit signal from each of the plurality of antenna elements to a passive power summing unit, as a remainder of the transmit signal from each of the plurality of antenna elements is transmitted.

5. The method of claim 1, further comprising the step of measuring the plurality of combined signals.

6. The method of claim 5, wherein said step of measuring the plurality of combined signals further comprises the step of:

filtering measurements due to anomalies or noise bursts.

7. The method of claim 5, wherein said measuring the plurality of combined signals includes passing each of the plurality of combined signals through a square law power detector and a low-pass filter, to measure the power of each of the plurality of combined signals.

8. The method of claim 7, wherein said pairwise combining includes determining a least squares fit solution for the arbitrary variables c₁ s₁ and ξ

in the matrix expression;

$\left(\begin{array}{c}{m}_1\\ m_2\\ \mathrm{⋮<br><br>}\\ m_N\end{array}\right)=\left(\begin{array}{ccc}\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_1& 1& \sin <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_1\\ \cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_2& 1& \sin <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_2\\ \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}\\ \cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_N& 1& \sin <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_N\end{array}\right)·<br><br>\left(\begin{array}{c}{c}_1\\ \mathrm{\xi <br><br>}\\ s_1\end{array}\right).$

where

Δ

<sub>1′

. . . N</sub>=sequence of prescribed phase values, and

m_{1 . . . N}=combined signal measurements, and determining the phase error e of said antenna element being calibrated as

e=arctan (−

s₁ c₁).

9. The method of claim 8, wherein said pairwise combining further includes determining a least squares fit solution for the arbitrary variables k₁ and k₂ in the matrix expression:

$\left(\begin{array}{c}{m}_1\\ m_2\\ \mathrm{⋮<br><br>}\\ m_N\end{array}\right)=\left(\begin{array}{cc}1& \cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\left({\mathrm{\Delta <br><br>}}_1+\hat{e}\right)\\ 1& \cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\left({\mathrm{\Delta <br><br>}}_2+\hat{e}\right)\\ \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}\\ 1& \cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\left({\mathrm{\Delta <br><br>}}_N+\hat{e}\right)\end{array}\right)·<br><br>\left(\begin{array}{c}{k}_1\\ k_2\end{array}\right)$

and solving the equation;

$a_{1,2}=\frac{k_1}{k_2}\pm <br><br>\sqrt{{\left(\frac{k_1}{k_2}\right)}^2-1}$

wherein

ê

is an estimate of e and

either the value of a₁ or a₂ is determined to be the ratio of the signal amplitude of the one of the plurality of antenna elements to the signal amplitude of the arbitrarily selected reference element, based on whether the transmit power of the one of the plurality of antenna elements is greater than or less than the transmit power of the arbitrarily selected reference element.

10. The method of claim 9, wherein when said transmit power of the one of the plurality of antenna elements is less than said transmit power of the arbitrarily selected reference element, said ratio is determined to be the value of a₁ or a₂ which is less than one and when said transmit power of the one of the plurality of antenna elements is greater than said transmit power of the arbitrarily selected reference element, said ratio is determined to be the value of a₁ or a₂ which is greater than one.

11. A method of calibrating an antenna element, arbitrarily selected from a plurality of such antenna elements, said antenna elements making up a receive phased array antenna, said method comprising the steps of:

applying a respective one of a plurality of receive signals, which each initially has the same defined amplitude and phase, to each of the plurality of antenna elements;

maintaining the phase and amplitude of the one of said receive signals that is applied to the arbitrarily selected antenna element as it is initially, while rotating the phase of the respective receive signals applied to each of the plurality of antenna elements, other than the receive signal supplied to the arbitrarily selected antenna element, through a sequence of prescribed phase steps;

at each prescribed phase step of said sequence, combining each of the receive signals from each of said plurality of antenna elements with the receive signal from the arbitrarily selected reference element in pairwise fashion to produce a plurality of combined signals; and

determining a phase error and amplitude error for each of the plurality of antenna elements based on the plurality of combined signals.

12. The method of claim 11, wherein said phase of the receive signal applied to each of said antenna elements is rotated using a direct digital synthesizer (DDS) corresponding to each of the plurality of antenna elements.

13. The method of claim 11, wherein the phase of the receive signal applied to each of the plurality of antenna elements is rotated using a direct digital synthesizer (DDS) corresponding to each of the plurality of antenna elements.

14. The method of claim 11, further comprising the step of measuring the plurality of combined signals.

15. The method of claim 14, wherein said step of measuring the plurality of combined signals further comprises the step of:

filtering measurements due to anomalies or noise bursts.

16. The method of claim 14, wherein said measuring the plurality of combined signals includes passing each of the plurality of combined signals through a square law power detector and a low-pass filter, to measure the power of each of the plurality of combined signals.

17. The method of claim 16, wherein said pairwise combining includes determining a least squares fit solution for the arbitrary variables c₁, s₁, and ξ

in the matrix expression;

$\left(\begin{array}{c}{m}_1\\ m_2\\ \mathrm{⋮<br><br>}\\ m_N\end{array}\right)=\left(\begin{array}{ccc}\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_1& 1& \sin <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_1\\ \cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_2& 1& \sin <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_2\\ \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}\\ \cos <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_N& 1& \sin <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\Delta <br><br>}}_N\end{array}\right)·<br><br>\left(\begin{array}{c}{c}_1\\ \mathrm{\xi <br><br>}\\ s_1\end{array}\right)$

where

Δ

_{1 . . . N}=sequence of prescribed phase values, and

m_{1 . . . N}=combined signal measurements, and determining the phase error e of said antenna element being calibrated as

e=arctan (−

s₁ c₁).

18. The method of claim 17, wherein said pairwise combining further includes determining a least squares fit solution for the arbitrary variables k₁ and k₂ in the matrix expression:

$\left(\begin{array}{c}{m}_1\\ m_2\\ \mathrm{⋮<br><br>}\\ m_N\end{array}\right)=\left(\begin{array}{cc}1& \cos <br><br>\left({\mathrm{\Delta <br><br>}}_1+\hat{e}\right)\\ 1& \cos <br><br>\left({\mathrm{\Delta <br><br>}}_2+\hat{e}\right)\\ \mathrm{⋮<br><br>}& \mathrm{⋮<br><br>}\\ 1& \cos <br><br>\left({\mathrm{\Delta <br><br>}}_N+\hat{e}\right)\end{array}\right)·<br><br>\left(\begin{array}{c}{k}_1\\ k_2\end{array}\right)$

and solving the equation;

$a_{1,2}=\frac{k_1}{k_2}\pm <br><br>\sqrt{{\left(\frac{k_1}{k_2}\right)}^2-1}$

wherein

ê

is an estimate of e and

either the value of a₁ or a₂ is determined to be the ratio of the signal amplitude of the one of the plurality of antenna elements to the signal amplitude of the arbitrarily selected reference element, based on whether the transmit power of the one of the plurality of antenna elements is greater than or less than the transmit power of the arbitrarily selected reference element.

19. The method of claim 18, wherein when said receive power of the one of the plurality of antenna elements is less than said receive power of the arbitrarily selected reference element, said ratio is determined to be the value of a₁ or a₂ which is less than one and when said receive power of the one of the plurality of antenna elements is greater than said receive power of the arbitrarily selected reference element, said ratio is determined to be the value of a₁ or a₂ which is greater than one.

20. A controller for calibrating an antenna element, arbitrarily selected from a plurality of such antenna elements, said antenna elements making up a transmit phased array antenna, said controller comprising:

a phase and amplitude controller that maintains a phase and amplitude of a transmit signal that is applied to the arbitrarily selected antenna element as it is initially, while rotating a phase of transmit signals applied to each of the plurality of antenna elements, other than the transmit signal supplied to the arbitrarily selected antenna element, through a sequence of prescribed phase steps;

a combiner that combines each of the transmit signals from each of said plurality of antenna elements with the transmit signal from arbitrarily selected antenna element, at each prescribed phase step of said sequence, in pairwise fashion, thereby producing a plurality of combined signals; and

a calibration unit that determines a phase error and amplitude error for each of the plurality of antenna elements other than the arbitrarily selected antenna element based on the plurality of combined signals.

21. A transmit system including the controller of claim 20.

22. A controller for calibrating an antenna element, arbitrarily selected from a plurality of such antenna elements, said antenna elements making up a receive phased array antenna, said controller comprising:

a phase and amplitude controller for maintaining a phase and amplitude of a receive signal that is applied to the arbitrarily selected antenna element as it is initially, while rotating a phase of receive signals applied to each of the plurality of antenna elements other than the receive signal supplied to the arbitrarily selected antenna element through a sequence of prescribed phase steps;

a combiner for combining each of the receive signals from each of said plurality of antenna elements with the receive signal from arbitrarily selected antenna element, at each prescribed phase step of said sequence, in pairwise fashion to produce a plurality of combined signals; and

a calibration unit for determining a phase error and amplitude error for each of the plurality of antenna elements other than the arbitrarily selected antenna element based on the plurality of combined signals.

23. A receive system including the controller of claim 22.

24. A controller for calibrating an antenna element, arbitrarily selected from a plurality of such antenna elements, said antenna elements making up a transmit phased array antenna, said controller comprising:

phase and amplitude control means for maintaining the phase and amplitude of a transmit signal that is applied to the arbitrarily selected antenna element as it is initially, while rotating a phase of transmit signals applied to each of the plurality of antenna elements, other than the transmit signal supplied to the arbitrarily selected antenna element, through a sequence of prescribed phase steps;

combining means for combining each of the transmit signals from each of said plurality of antenna elements with the transmit signal from the arbitrarily selected antenna element, at each prescribed phase step of said sequence, in pairwise fashion to produce a plurality of combined signals; and

calibration means for determining a phase error and amplitude error for each of the plurality of antenna elements other than the arbitrarily selected antenna element based on the plurality of combined signals.

25. A transmit system including the controller of claim 24.

26. A controller for calibrating an antenna element, arbitrarily selected from a plurality of such antenna elements, said antenna elements making up a receive phased array antenna, said controller comprising:

phase and amplitude control means for maintaining a phase and amplitude of a receive signal that is applied to the arbitrarily selected antenna element as it is initially, while rotating a phase of receive signals applied to each of the plurality of antenna elements, other than the receive signal supplied to the arbitrarily selected antenna element, through a sequence of prescribed phase steps;

combining means for combining each of the receive signals from each of said plurality of antenna elements with the receive signal from the arbitrarily selected antenna element, at each prescribed phase step of said sequence, in pairwise fashion to produce a plurality of combined signals; and

calibration means for determining a phase error and amplitude error for each of the plurality of antenna elements other than the arbitrarily selected antenna element based on the plurality of combined signals.

27. A receive system including the controller of claim 26.

28. A computer program embodiment on a medium, said computer program causing a processor to calibrate an antenna element arbitrarily selected from a plurality of such antenna elements, said antenna elements making up a phased array antenna, said computer program comprising:

a phase rotating segment means for maintaining a phase and amplitude of a signal that is applied to the arbitrarily selected antenna element as it is initially, while rotating a phase of signals applied to each of the plurality of antenna elements, other than the signal supplied to the arbitrarily selected antenna element, through a sequence of prescribed phase steps;

a combining code segment means for combining, at each prescribed phase step of said sequence, each of the signals from each of said plurality of antenna elements with the signal from the arbitrarily selected antenna element in pairwise fashion to produce a plurality of combined signals; and

a determining code segment means for determining a phase error and amplitude error for each of the plurality of antenna elements other than the arbitrarily selected antenna element based on the plurality of combined signals.

29. The computer program of claim 28, wherein the signals are one of transmit and receive signals.