Active antenna array and method for calibration of receive paths in said array

1. An active antenna array for a mobile communications system comprising:

a plurality of receive paths, for carrying a plurality of analogue receive signals, an individual one of the receive paths being connected between an individual one of a plurality of antenna elements and an individual one of a plurality of analogue to digital converters;

a sounding signal generator for generating a digital sounding signal;

wherein an analogue sounding signal, based on the digital sounding signal, is injected to at least two of the plurality of receive paths; and

wherein, for each receive path of said at least two of the plurality of receive paths, the individual one of the plurality of analogue to digital converters is configured to digitize the analogue receive signal and the analogue sounding signal to form a digitized receive signal;

a receive signal subtraction device for subtracting a processed digitized receive signal from the digitized receive signal to generate a processed digitized sounding signal; and a sounding signal subtraction device for subtracting the digital sounding signal from the digitized receive signal to form the processed digitized receive signal.

2. The active antenna array of claim 1 , wherein a digital to analogue converter is connected between the sounding signal generator and the at least two of the plurality of receive paths.

3. The active antenna array of claim 1 , wherein the sounding signal generator is adapted to produce at least one of a plurality of inter-band digital sounding signals or broad-brand digital sounding signals.

4. The active antenna array of claim 1 , wherein one of the receive paths is a reference receive path without the injected digital sounding signal and therefor used only for carrying the processed digitized receive signal.

5. The active antenna array of claim 1 , wherein the analogue to digital converters are delta-sigma analogue to digital converters.

6. The active antenna array of claim 1 , wherein the individual one of the receive paths further comprises a duplex filter between the individual one of the plurality of analogue to digital converters and the individual one of the plurality antenna elements, the duplex filter being adapted to enable transmit signals to be transmitted on the individual one of the plurality of antenna elements.

7. The active antenna array of claim 6 , wherein the individual one of the plurality of analogue to digital converters is connected to the receive path between the duplex filter and the individual one of the plurality of antenna elements.

8. The active antenna array of claim 1 , further comprising, on each receive path of the plurality of receive paths, an individual one of the plurality of filter elements to filter unwanted signals from the digitized receive signals.

9. The active antenna array of claim 1 , further comprising:

a receive signal correlator and control system for adjusting one of the phase, amplitude or vector of the digitized receive signal.

10. The active antenna array of claim 1 , further comprising:

a sounding signal correlator and control system for adjusting one of the phase, amplitude or vector of the digital sounding signal.

11. The active antenna array of claim 1 , wherein a digital signal processor generates an I/Q baseband output signal, for each receive path of the plurality of receive paths, based on the processed digitized receive signal for each receive path of the plurality of receive paths.

12. A method for calibration of a plurality of receive paths carrying analogue receive signals comprising:

generating a digital sounding signal;

converting the digital sounding signal to form an analogue sounding signal;

injecting the analogue sounding signal into at least two of the plurality of receive paths;

digitizing, for each receive path of said at least two of the plurality of receive paths, the analogue receive signal and the analogue sounding signal to form a digitized receive signal;

subtracting, for each receive path of said at least two of the plurality of receive paths, a processed digitized receive signal from the digitized receive signal to form a processed digitized sounding signal; and

subtracting the digital sounding signal from the digitized receive signal to form the processed digitized receive signal.

13. The method of claim 12 , further comprising generating parameters for processing the processed digitized receive signal, wherein the parameters are generated by comparing the processed digitized sounding signal and the digital sounding signal.

14. The method of claim 12 , wherein one of the receive paths is a preferential receive path without the infected digital sounding signal and therefor used only for carrying the processed digitized receive signal and the parameters are generated by reference to the preferential receive path.

15. The method of claim 12 further comprising:

adjusting one of phase, amplitude or vector of the digitized receive signals.

16. The method of claim 12 further comprising:

adjusting one of phase amplitude or vector of the digital sounding signal.

17. The method of claim 12 , further comprising:

generating an I/Q baseband output signal, for each receive path of the plurality of receive paths, based on the processed digitized receive signal for each receive path of the plurality of receive paths.

18. A computer program product comprising a non-transitory computer-usable medium having control logic stored therein for causing a computer to manufacture an active antenna array for a mobile communications network comprising:

a plurality of receive paths, for carrying a plurality of analogue receive signals, the individual one of the receive paths being connected between an individual one of a plurality of antenna elements and an individual one of the plurality of analogue to digital converters, the individual one of the plurality of analogue to digital converters digitizing an analogue receive signal;

a sounding signal generator for generating a digital sounding signal;

wherein an analogue sounding signal, based on the digital sounding signal, is injected to the at least two of the plurality of receive paths; and

for each receive path of said at least two of the plurality of receive paths, the individual one of the plurality of analogue to digital converters is configured to digitize the analogue receive signal and the analogue sounding signal to form a digitized receive signal;

a receive signal subtraction device for subtracting a processed digitized receive signal from the digitized receive signal to generate a processed digitized sounding signal; and a sounding signal subtraction device for subtracting the digital sounding signal from the digitized receive signal to form the processed digitized receive signal.

19. A computer program product comprising a non-transitory computer-usable medium having control logic stored therein for causing an active antenna to execute a method for receiving analogue receive signals comprising:

generating a digital sounding signal;

converting the digital sounding signal to form an analogue sounding signal;

injecting the analogue sounding signal into at least two of the plurality of receive paths

digitizing, for each receive path of said at least two of the plurality of receive paths, the analogue receive signal and the analogue sounding signal to form a digitized receive signal; and

subtracting a processed digitized receive signal from the digitized receive signal to generate a processed digitized sounding signal; and

subtracting the digital sounding signal from the digitized receive signal to form the processed digitized receive signal.