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 (308a, 308b), the beamformer having a plurality of first polarization beamformer channels (348a, 500) and second polarization beamformer channels (348b, 500), 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 (308a, 308b); 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 (372, 734); and in a second mode to: configure at least one first polarization beamformer channel (348a, 348b, 500) 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. 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 (308a, 308b), the beamformer having a plurality of first polarization beamformer channels (348a, 500) and second polarization beamformer channels (348b, 500), 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 (308a, 308b); 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 (372, 734); and in a second mode to: configure at least one first polarization beamformer channel (348a, 348b, 500) 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. a digital pre-distortion module coupled to the first and second polarization radio chains (308a, 308b); 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 (372, 734); and in a second mode to: configure at least one first polarization beamformer channel (348a, 348b, 500) 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. configure at least one first polarization beamformer channel (348a, 348b, 500) 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.