Communication unit and method of antenna array calibration

• US 10,090,940 B2
• Filed: 08/15/2014
• Issued: 10/02/2018
• Est. Priority Date: 08/16/2013
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Analog Devices Global Unlimited Company (Analog Devices, Inc.)
• Inventors: O'Keeffe, Conor, O'Brien, Michael, Sexton, Sean
• Primary Examiner(s): Maung, Nay A
• Assistant Examiner(s): Soltanzadeh, Maryam
• Application Number:
  US14/912,065
• Publication Number:
  US 20160191176A1
• Time in Patent Office: 1,509 Days
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices
• CPC Class Codes: H04B 17/00 Monitoring; Testing of line transmission systems H04B3/46; arrangements for monitoring or testing transmission systems employing electromagnetic waves other than radio waves H04B10/07
• CPC Class Codes: H04B 17/11 for calibration
• CPC Class Codes: H04B 7/0617 for beam forming

Abstract

A method for calibrating an antenna array coupled to a plurality of transmitters via a plurality of couplers and a plurality of antenna element feeds is described. The method comprises, at a communication unit: selecting and coupling at least one coupler to a calibration receiver in a feedback path in the communication unit; scaling at least one first signal by at least one first beamform weight; applying the scaled at least one first signal to a first transmitter of the plurality of transmitters and routing the scaled at least one first signal via the selected at least one coupler to the calibration receiver; generating a reference signal by selecting and scaling the at least one first signal by at least one second beamform weight substantially equal to the at least one first beamform weight; comparing the at least one first signal scaled with the at least one first beamform weight with the at least one first signal reference signal scaled by the at least one second beamform weight to determine at least one first parameter result; storing the at least one first parameter result of the comparison associated with the first transmitter; repeating for subsequent transmitters the steps of selecting and coupling a further coupler, scaling, applying at least one further signal to a further transmitter of the plurality of transmitters, generating a further reference signal, comparing and storing at least one further parameter result until the plurality of couplers have been selected; and determining at least one calibration correction coefficient from a plurality of parameter results for applying to at least one second signal input to at least one transmitter of the plurality of transmitters coupled to the antenna array to substantially equalize a transfer function of a plurality of transmit paths to antenna element feeds for the at least one second signal having beamform weights applied thereto.

Claims

1. A method for calibrating an antenna array configured to transmit signals associated with sectored beams, the antenna array coupled to a plurality of transmitters via a plurality of antenna element feeds, the method comprising

scaling at least one first signal by at least one first beamform weight to form a scaled first signal;

providing the scaled at least one first signal to a first transmitter of the plurality of transmitters,

outputting, from the first transmitter, a first transmitter output signal associated with at least a first sectored beam and a second sectored beam to an antenna element feed of the plurality of antenna element feeds;

sending a feedback signal to a calibration receiver, wherein the feedback signal is indicative of the first transmitter output signal such that the feedback signal is associated with at least the first sectored beam and the second sectored beam;

generating a reference signal by selecting and scaling the at least one first signal by at least one second beamform weight substantially equal to the at least one first beamform weight;

comparing a processed version of the feedback signal with a processed version of the reference signal to determine at least one first parameter result; and

storing the at least one first parameter result.

2. The method of claim 1 further comprising:

selecting and coupling at least one coupler to the calibration receiver; and

routing the feedback signal to the calibration receive via the at least one coupler.

3. The method of claim 2 further comprising:

repeating for subsequent transmitters of the plurality of transmitters, the operations of selecting and coupling a further coupler, scaling a further signal by a further beamforming weight to generate at least one further scaled signal, providing the at least one further scaled signal to a further transmitter of the plurality of transmitters, outputting a further transmitter output signal, sending a further reference signal, generating a further reference signal, comparing and storing at least one further parameter result until each of the plurality of couplers have been selected; and

determining at least one calibration correction coefficient from a plurality of parameter results for applying to at least one second signal input to at least one transmitter of the plurality of transmitters coupled to the antenna array to substantially equalize a transfer function of a plurality of transmit paths to antenna element feeds for the at least one second signal having beamform weights applied thereto.

4. The method of claim 1 wherein said comparing comprises at least one of a least mean squares error determination or a minimum mean squares error determination.

5. The method of claim 1 wherein determining at least one first parameter result comprises determining that a result of said comparing falls within a specific range of results, and wherein the method further comprises running a fault detection sequence in response to determining that the result of said comparing is outside of the specified range of results.

6. The method of claim 1 wherein the first sectored beam and the second sectored beams are sectorized in at least one of a vertical plane or a horizontal plane.

7. A method for calibrating an antenna array coupled to a plurality of transmitters via a plurality of couplers and a plurality of antenna element feeds, the method comprising:

scaling a first signal by a first beamform weight and scaling a second signal by a second beamform weight, wherein the first signal and the second signal are associated with different sectored beams;

transmitting, with a first transmitter of the plurality of transmitters, a first transmitter output signal associated with a combination of the scaled first signal and the scaled second signal such that the first transmitter output signal is associated with at least two sectored beams;

generating a reference signal by at least combining a first scaled calibration signal with a second scaled calibration signal, wherein the scaled first calibration signal corresponds to the first signal scaled by a first calibration beamform weight, and wherein the scaled second calibration signal corresponds to the second signal scaled by a second calibration beamform weight; and

computing a calibration correction coefficient associated with a selected transmitter of the plurality of transmitters based at least partly on a comparison of a processed version of the reference signal with a processed version of a feedback signal that is indicative of the first transmitter output.

8. The method of claim 7, wherein computing the calibration coefficient is further based on a comparison of a second feedback signal associated with a second transmitter of the plurality of transmitters with a second reference signal associated with the second transmitter.

9. The method of claim 7, further comprising normalizing the calibration coefficient associated with the selected transmitter relative to a calibration coefficient associated with a different transmitter of the plurality of transmitters.

10. The method of claim 7, further comprising applying the calibration coefficient such that a transmit path associated with the selected transmitter has a transfer function that is substantially equalized with transmit paths of other transmitters of the plurality of transmitters.

11. The method of claim 7, wherein the first calibration beamform weight is substantially equal to the first beamform weight, and the second calibration beamform weight is substantially equal to the second beamform weight.

12. A communication unit for transmitting signals associated with sectored beams, the communication unit comprising:

a plurality of transmitters each operatively coupleable to an antenna array, wherein a first transmitter of the plurality of transmitters comprises;

a beamformer configured to scale a first signal by a first weight and to scale a second signal by a second weight that is independent of the first weight, wherein the first signal and the second signal are associated with different sectored beams, and

wherein the first transmitter is configured to output a first transmit signal associated with a combination of the scaled first signal and the scaled second signal such that the first transmit signal is associated with the different sectored beams;

a calibration transceiver configured to receive the first signal, the second signal, and a feedback signal indicative of the first transmit signal, the calibration transceiver comprising;

a signal generator configured to generate a reference signal by at least scaling the first signal by a first calibration weight, scaling the second signal by a second calibration weight, and combining the scaled first signal with the scaled second signal; and

a compare circuit configured to compare a processed version of the reference signal with a processed version of the feedback signal; and

a memory operatively coupled to the compare circuit, the memory configured to store data representative of a result of the comparison of the compare circuit.

13. The communication unit of claim 12, wherein the compare circuit comprises an adaptive filter.

14. The communication unit of claim 12, further comprising:

a plurality of couplers operatively coupled between respective transmitters of the plurality of transmitters and the antenna array; and

a switch matrix configured to operatively couple a selected coupler of the plurality of couplers to the calibration transceiver to thereby provide the feedback signal to the calibration transceiver.

15. The communication unit of claim 12, further comprising a processor configured to determine a calibration coefficient associated with the first transmitter based on the data representative of the result of the comparison of the compare circuit stored in the memory.

16. The communication unit of claim 15, wherein the memory is configured to store second data representative of a second result of a second comparison performed by the compare circuit, wherein the second comparison involves a processed version of a second reference signal associated with a second transmitter of the plurality of transmitters and a processed version of a second feedback signal associated with the second transmitter, and wherein the processor is configured to determine the calibration coefficient based on the data and the second data.

17. The communication unit of claim 12, wherein the first sectored beam is supported by two logical channels associated with different antenna element polarizations.

18. The communication unit of claim 12, further comprising a single antenna element feed configured to receive the first transmit signal.

19. The communication unit of claim 12, wherein the first transmitter is configured to provide the first transmit signal to a single antenna element of the antenna array, and the single antenna element is configured to transmit the first transmit signal.

20. The communication unit of claim 12, wherein the first transmitter comprises summing logic configured to combine the scaled first signal and the scaled second signal.