| CPC H01Q 3/34 (2013.01) [H01Q 5/28 (2015.01); H04B 1/0475 (2013.01); H04B 2001/0425 (2013.01)] | 20 Claims |

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1. A multiple-input multiple-output, MIMO, antenna system for a mobile cellular network, the antenna system comprising:
an array of dual-polarized antennas, each dual-polarized antenna having a first polarization feed-point and a second polarization feed-point;
a first polarization radio chain;
a second polarization radio chain;
a beamformer coupled to the first and second polarization radio chains, the beamformer having a plurality of first polarization beamformer channels and second polarization beamformer channels, each of the first polarization beamformer channels coupled to a first polarization feed-point of a respective dual-polarization antenna and each of the second polarization beamformer channels coupled to a second polarization feed-point of the respective dual-polarization antenna, wherein each beamformer channel comprises a transmit amplifier and a detector coupled to a transmit amplifier output; and wherein the MIMO antenna system further comprises:
a digital pre-distortion module coupled to the first and second polarization radio chains; and
a controller having a control output coupled to the beamformer; and wherein the controller is operable to control the beamformer in a first mode to:
configure the beamformer to transmit or receive an RF signal via the respective first and second polarization feed-points; and in a second mode to:
configure at least one first polarization beamformer channel to transmit an RF signal to a respective first polarization feed-point and to couple a detector output of the at least one first polarization beamformer channel to the second polarization radio chain;
transmit an RF signal via the first polarization radio chain;
detect a replica of the RF signal via the second polarization radio chain;
and wherein the digital pre-distortion module is configured to digitally pre-distort a signal for transmission dependent on the replica of the RF signal.
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