Method and apparatus for calibrating phased array receiving antennas

• US 5,248,982 A
• Filed: 07/15/1992
• Issued: 09/28/1993
• Est. Priority Date: 08/29/1991
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (AT&T, Inc.)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Reinhardt, Victor S., Berman, Arnold L.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US07/914,187
• Time in Patent Office: 440 Days
• Field of Search: 342/174, 342/369, 342/375, 342/371, 342/372, 342/377
• US Class Current: 342/375
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices

Abstract

Disclosed is a method and apparatus for calibrating phased array receiving antennas that includes circuitry for generating a pair of calibration signals separable one from the other. The signals are injected into the delay elements of the antenna from opposite ends of a complementary calibration cable. The delay produced in the calibration signals is individually measured, and the delays summed and averaged to produce a delay measurement independent of delays produced by the calibration cable and accordingly delay measurement variations caused by environmental effects on the calibration cable.

Claims

1. A calibrator for calibrating phased array antennas which include a plurality of individual antenna receiving and delay elements, the calibrator comprising:

calibration signal generating means for generating first and second separable calibration signals;

calibration cable means including a calibration signal cable having opposite ends connected to respective outputs of the calibration signal generating means for receiving respective ones of the first and second calibration signals;

calibration signal injecting means connecting the calibration signal cable to inputs of each of the antenna receiving elements;

power summing means coupled to outputs of the antenna delay elements;

delay measurement means coupled to the calibration signal generating means and to the power summing means for measuring calibration signal delays or phase shifts of the first and second calibration signals at outputs of each of the antenna delay elements; and

computer means coupled between the delay measurement means and the antenna delay elements for summing and averaging the measured signal delays or phase shifts in the first and second calibration signals, and for adjusting the signal delays or phase shifts of selected antenna delay elements in response thereto.

2. The calibrator of claim 1 wherein the calibration cable is a complementary calibration cable.

3. The calibrator of claim 2 wherein the delay in the first and second calibration signals produced by propagation of the calibration signals over the length of the calibration cable is A, the delay caused by the calibration cable in the calibration signal propagating from the calibration signal generating means to an antenna element k is X_k, and the delay in the first and second calibration signals arriving at the antenna element is A-X_k.

4. The calibrator of claim 1 wherein the first and second calibration signals are sine wave signals of different closely spaced frequencies.

5. The calibrator of claim 1 wherein the first and second calibration signals are spread spectrum signals having orthogonal codes.

6. The calibrator of claim 5 wherein the computer means further comprises, means for applying a smoothing algorithm to the measured phase shifts of the first and second calibration signals for eliminating phase ambiguities therebetween.

7. The calibrator of claim 1 wherein the first and second calibration signals are two simultaneously occurring calibration signals of differing calibration signal frequencies transmitted in opposite directions to said plurality of antenna receiving elements.

8. The calibrator of claim 3 wherein the computer means is adapted to measure and compute the average delay of the first and second calibration signals caused by each antenna element in accordance with the relationship (x_k +x'"'"'_k)/2=(x_ek +x'"'"'_ek)/2+A/2, where X_ek is the delay in the first calibration signal produced by a delay element k and X'"'"'_ek is the delay in the second calibration signal produced by a delay element k.

9. The calibrator of claim 3 wherein the computer means is adapted to measure and compute the average phase shift between the first and second calibration signals caused by each antenna element in accordance with the relationship φ

_ek =(f_c '"'"'φ

_k +f_c φ

_k '"'"')/(f_c '"'"'+f_c)+constant, where φ

_ek is the phase shift for element k at f_c, f_c and f_c '"'"' are frequencies, and where φ

_k and φ

_k '"'"' are the measured phase shifts.

10. The calibrator of claim 1 wherein the delay elements are analog delay elements.

11. The calibrator of claim 1 wherein the delay elements are digital delay elements.

12. A method for calibrating a phased array receiving antenna which includes an array of individual antenna receiving elements and delay elements, comprising the steps of:

injecting first and second separable calibration signals into each of the delay elements of the antenna through opposite ends of a complementary calibration cable connected to the inputs thereof;

measuring the delay in the first calibration signal produced by a delay element k;

measuring the delay in the second calibration signal produced by a delay element k;

summing and averaging a delay in the first and second calibration signals to generate an average delay produced by the delay element independent of the delay produced therein by the calibration cable.

13. The method of claim 12 wherein the first and second calibration signals are sine wave signals of different closely spaced frequencies.

14. The method of claim 13 wherein the frequency of the calibration signals is at or near the operating frequency of the phased array antenna.

15. The method of claim 12 wherein the first and second calibration signals are orthogonally coded spread spectrum signals.

16. The calibrator of claim 15 wherein the carrier frequency of the spread spectrum signals are of different frequencies at or near the center operating frequency of the phased array antenna.

17. The method of claim 12 wherein the first and second calibration signals are two simultaneously occurring calibration signals having different frequencies in the operating frequency range of the phased array antenna and being transmitted in opposite directions to said array of individual antenna receiving elements.