Array antenna calibration

• US 20010011961A1
• Filed: 01/31/2001
• Published: 08/09/2001
• Est. Priority Date: 02/01/2000
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Rexberg, Leonard, Johansson, Bernt
• Granted Patent: US 6,462,704 B2
• Time in Patent Office: Days
• US Class Current: 342/368
• CPC Class Codes: G01S 7/4017 of HF systems
• CPC Class Codes: H01Q 3/267 Phased-array testing or checking devices

Abstract

A method and a system for an array antenna calibration are disclosed. The method and system provide a sensor system presenting a sensor device (3) at each antenna element (1), which sensor devices constitute simple digital receivers. Each digital receiver produces a complex base-band I/Q-signal. The outputs of the digital receivers are fed to a Digital Signal Processing device for adding them up to obtain a resulting signal which when converted to a DC signal presents a maximum if all individual signals have the same phase. The search for a maximum of this DC voltage is then used by the Digital Signal Processor for creating source signal phase control signals. By adjusting source signal phases for obtaining maximum added DC voltage derived from the sensor system the phases at the antenna elements will be calibrated. In this manner an adaptive array antenna is simply calibrated even during operation by compensating the base-band I/Q-signals for the intentional phase settings used for achieving a specific channel adaptive array antenna direction.

Claims

1. A method for an array antenna calibration comprising the steps of providing a sensor system presenting a sensor device at each antenna element, said sensor devices constituting simple digital receivers and each digital receiver producing a respective complex base-band I/Q-signal;

providing present beam pointing angle signal phase off-set information and converting base band I/Q-signals into new complex signals corresponding to a broad-side beam direction;

producing crosswise signal correlation values from acquired new complex signals by a digital processing device for filtering out time dependent portions of said complex signals;

normalizing and adding achieved signal correlation values to arrive at a summed DC voltage that will present a maximum when all sensed antenna element signals corresponding to a broad-side direction are in phase;

adjusting signal phase of each antenna element source signal by a device for controlling signal phase in order to obtain maximum summed DC voltage achieved from the sensor system base band signals.

2. The method according to

claim 1

, comprising the further step of localizing said sensor device to pick up antenna element signals at an antenna contact level.

3. The method according to

claim 1

, comprising the further step of using 8 bit A/D converters in said simple digital receivers forming said sensor system for acquiring digital base-band I/Q-signals.

4. The method according to

claim 1

, comprising the further step of transferring acquired complex signals for further processing to a processing device in the base station using a same feed cable as for RF transmission to an antenna element making extra cables unnecessary.

5. The method according to

claim 1

, comprising the further step of using a base station Digital Signal Processor cluster as processing device for calculating signal correlation values when forming said summed DC voltage to be maximized and as the device for controlling the phase of the array antenna source signals for maximizing obtained DC voltage.

6. The method according to

claim 1

, comprising the further step of applying a Newton-Raphson search algorithm for finding a maximum of the obtained DC voltage when adjusting signal phase of each antenna element source signal.

7. The method according to

claim 1

, comprising the further step of performing an initial adjustment of the antenna element source signals if having too large amplitude differences in antenna signal branches, by using only paired signals from the sensor system and adjusting the phase of one of the corresponding two source signals for a resulting maximum DC voltage derived from two base-band sensor signals to a value of twice the value of that for a single sensor and repeating this for all available pairs of signals until all of the signal branches has been calibrated in this way.

8. A system for an array antenna calibration comprising

a sensor system presenting a local sensor device at each antenna element, the sensor devices constituting simple digital receivers, each digital receiver producing a complex base-band I/Q-signals, achieved complex base-band I/Q-signals being converted into new complex signals corresponding to a broad-side beam direction by compensating for present beam pointing angle off-set;

a digital processing device for producing crosswise signal correlation values from acquired new complex signals for filtering out time dependent components of the acquired new complex signals, the obtained correlation values being normalized and summed to arrive at a summed DC voltage, which will present a maximum value when all sensed antenna element signals corresponding to a broad-side direction are properly phased, and

a control means for obtaining a maximum summed DC voltage by adjusting the phase of each antenna element source signal to thereby obtain a proper array antenna system signal phasing.

9. The system according to

claim 8

, wherein each sensor device for picking up antenna element signals is localized at an antenna contact level.

10. The system according to

claim 8

, wherein 8 bit A/D converters are utilized in the simple digital receivers forming the sensor system for acquiring digital base-band I/Q-signals.

11. The system according to

claim 8

, wherein acquired digital complex signals are transferred to a processing means in the base station using a corresponding feed cable as for RF transmission to an antenna element which makes extra cables unnecessary.

12. The system according to

claim 8

, wherein a base station Digital Signal Processor cluster is used as processing means for calculating signal correlation values and as a device for controlling the phase of the array antenna source signals.

13. The system according to

claim 8

, wherein a Newton-Raphson search algorithm is applied for finding a maximum value of the summed DC voltage when adjusting signal phases of each antenna element source signal.

14. The system according to

claim 8

, wherein an initial adjustment of antenna branches is performed, when having large signal differences in the antenna signal branches, by using only paired signals from the sensor system and adjusting the phase of one of the corresponding two source signals for a resulting maximum DC voltage derived from two base-band sensor signals to a value of twice the value of that for a single sensor, whereby this is repeated for all available pairs of signals until all of the signal branches has been calibrated in this way.