Apparatus and method for use with antenna array

1. An apparatus for feeding an antenna array comprising at least first and second antenna elements, the apparatus comprising:

a first transmitting element configured to receive a first base band signal and to feed a first feed signal to a first antenna element, the first transmitting element comprising a first power amplifier;

a second transmitting element configured to receive a second base band signal and to feed a second feed signal to a second antenna element; the second transmitting element comprising a second power amplifier; and

a tapering control unit adapted to provide a tapering function between the first feed signal to the first antenna element and the second feed signal to the second antenna element,

wherein the tapering control unit is adapted to provide first and second control signals for individually controlling bias settings of the first power amplifier and the second power amplifier, respectively, according to the tapering function provided between the first and second feed signals, and

wherein the controlling of bias setting comprises controlling a supply voltage provided to the first power amplifier and the second power amplifier to fit a power capability need created by the tapering function.

2. An apparatus as claimed in claim 1 , further comprising: a first biasing circuit for controlling the bias settings of the first power amplifier; a second biasing circuit for controlling the bias settings of the second power amplifier; wherein the first biasing circuit and the second biasing circuit are coupled to receive the first control signal and the second control signal from the tapering control unit, and wherein the first and second control signals are digital signals for controlling the respective biasing circuits.

3. An apparatus as claimed in claim 1 , wherein the tapering control unit is adapted to control the bias settings of the first and second power amplifiers to set a power output capability and/or power dissipation of the first and second power amplifiers according to the tapering function.

4. An apparatus as claimed in claim 1 , wherein the tapering control unit is configured to dynamically adapt one or more bias settings in response to changes in the characteristics of the tapering function.

5. An apparatus as claimed in claim 1 , further comprising: a first multiplier unit provided in the path of the first base band signal; a second multiplier unit provided in the path of the second base band signal; wherein the first multiplier unit and the second multiplier unit are controlled by the tapering control unit, and configured to adjust the amplitude and/or phase of the first base band signal and the second base band signal, respectively, to provide the tapering function between the first feed signal to the first antenna element and the second feed signal to the second antenna element.

6. An apparatus as claimed in claim 1 , wherein the tapering control unit is controlled by one or more signals received from an operations, administration and maintenance, OAM, system of a mobile communications system.

7. An apparatus as claimed in claim 1 , wherein each transmitting element further comprises a processing circuit for up-converting the first and second feed signals to respective radio frequency signals, for amplification by the respective power amplifier.

8. An apparatus as claimed in claim 1 , further comprising: a first adder circuit coupled to a signal flow of the first transmitting element; a second adder circuit coupled to a signal flow of the second transmitting element; wherein the tapering control unit is further adapted to provide first and second calibration signals via the first and second adder circuits to the first and second signal flows during a calibration mode of operation.

9. An apparatus as claimed in claim 8 , wherein the tapering control unit is coupled to receive:

a first feedback signal from the output of the first power amplifier;

a second feedback signal from the output of the second power amplifier;

wherein the control unit is further adapted to compare the first and second calibration signals with the first and second feedback signals, during a calibration mode of operation, and to regulate bias settings of the first and second power amplifiers based on the comparison of the first and second feedback signals with the first and second calibration signals.

10. An antenna array comprising a plurality of antenna elements, and an apparatus as claimed in claim 1 .

11. A method of providing a tapering function in an antenna array comprising at least first and second antenna elements, the method comprising the steps of:

amplifying a first base band signal using a first transmitting element comprising a first power amplifier, to provide a first feed signal for a first antenna element;

amplifying a second base band signal using a second transmitting element comprising a second power amplifier, to provide a second feed signal for a second antenna element;

providing a tapering function between the first feed signal to the first antenna element and the second feed signal to the second antenna element;

adding a first calibration signal to the first feed signal and a second calibration signal to the second feed signal during a calibration mode of operation;

receiving a first feedback signal from the output of the first power amplifier and a second feedback signal from the output of the second power amplifier during the calibration mode;

comparing the first and second calibration signals with the first and second feedback signals, during a calibration mode of operation; and

regulating the bias settings of the first and second power amplifiers based on the comparison of the first and second feedback signals with the first and second calibration signals.

12. A method as claimed in claim 11 , wherein the step of providing the tapering function further comprises the step of individually controlling bias settings of the first power amplifier and the second power amplifier according to the tapering function provided between the first antenna element and the second antenna element.

13. A method as claimed in claim 12 , wherein the bias settings of the first power amplifier and the second power amplifier are dynamically controlled during use of the antenna array.

14. A method as claimed in claim 13 , where in the bias settings are controlled according to information received from a mobile communications system.

15. A method as claimed in claim 11 , further comprising the steps of: adjusting the amplitude and/or phase of the first feed signal and the second feed signal to provide the tapering function between the first feed signal to the first antenna element and the second feed signal to the second antenna element.