A calibration method for characterising a beamforming network of a satellite payload, comprising: receiving (Sio) a reference signal and an encoded signal from the satellite payload, wherein the reference signal corresponds to a calibration signal, and the encoded signal comprises a sequence of signals defined by the application of an orthogonal, bipolar, invertible matrix to the calibration signal, wherein the matrix is arranged to sequentially toggle each of a first plurality of settings of the beamforming network; and performing a calibration procedure by determining the relative gain and phase difference between the reference signal and the encoded signal for each of the sequence of signals in the encoded signal to derive a composite vector of measurements, and applying the inverse matrix to the composite vector of measurements to provide a first decoded signal representing the effect of toggling of each of the first plurality of settings of the beamforming network on the complex gain differences; characterised by further comprising: applying an offset to one or more of the first plurality of settings of the beamforming network to derive a second plurality of settings of the beamforming network; applying the orthogonal, bipolar, invertible matrix to the calibration signal, wherein the matrix is arranged to sequentially toggle each of the second plurality of settings of the beamforming network and repeating the calibration procedure to output a second decoded signal representing the effect of toggling of each second plurality of beamforming network settings on the complex gain differences; outputting a characterisation of the beamforming network as sensitivity to changes in beamforming network parameters as a ratio between the first and second decoded signals. receiving (Sio) a reference signal and an encoded signal from the satellite payload, wherein the reference signal corresponds to a calibration signal, and the encoded signal comprises a sequence of signals defined by the application of an orthogonal, bipolar, invertible matrix to the calibration signal, wherein the matrix is arranged to sequentially toggle each of a first plurality of settings of the beamforming network; and performing a calibration procedure by determining the relative gain and phase difference between the reference signal and the encoded signal for each of the sequence of signals in the encoded signal to derive a composite vector of measurements, and applying the inverse matrix to the composite vector of measurements to provide a first decoded signal representing the effect of toggling of each of the first plurality of settings of the beamforming network on the complex gain differences; characterised by further comprising: applying an offset to one or more of the first plurality of settings of the beamforming network to derive a second plurality of settings of the beamforming network; applying the orthogonal, bipolar, invertible matrix to the calibration signal, wherein the matrix is arranged to sequentially toggle each of the second plurality of settings of the beamforming network and repeating the calibration procedure to output a second decoded signal representing the effect of toggling of each second plurality of beamforming network settings on the complex gain differences; outputting a characterisation of the beamforming network as sensitivity to changes in beamforming network parameters as a ratio between the first and second decoded signals. applying an offset to one or more of the first plurality of settings of the beamforming network to derive a second plurality of settings of the beamforming network; applying the orthogonal, bipolar, invertible matrix to the calibration signal, wherein the matrix is arranged to sequentially toggle each of the second plurality of settings of the beamforming network and repeating the calibration procedure to output a second decoded signal representing the effect of toggling of each second plurality of beamforming network settings on the complex gain differences; outputting a characterisation of the beamforming network as sensitivity to changes in beamforming network parameters as a ratio between the first and second decoded signals.