A method for calibrating a radar system of a wind turbine comprising a plurality of radar elements arranged in an array, each element comprising a radar transmitter and receiver for transmitting and receiving radar signals, the radar elements being operable to function in a transmit mode or a receive mode, the method comprising: - activating the transmit mode in a first antenna element of the array to transmit a test signal; - activating the receive mode in a second antenna element of the array proximate to the first antenna element, and positioned so as to receive radiation originating from a side lobe of the first antenna element; and - determining whether the second antenna element receives the test signal; the method further comprising: - activating the receive mode in at least one further antenna element of the array, proximate to the first antenna element, such that the second antenna element and each of the further antenna elements operate in receive mode while the first antenna element operates in transmit mode; the method being characterised by the following steps: - determining the relative phase and/or amplitude between the second antenna element and each of the further antenna elements; and/or - activating the transmit mode in at least one further antenna element of the array, proximate to the second antenna element, such that the first antenna element and each of the further antenna elements operate in transmit mode while the second antenna element operates in receive mode; and - determining the relative phase and/or amplitude between the first antenna element and each of the further antenna elements. - activating the transmit mode in a first antenna element of the array to transmit a test signal; - activating the receive mode in a second antenna element of the array proximate to the first antenna element, and positioned so as to receive radiation originating from a side lobe of the first antenna element; and - determining whether the second antenna element receives the test signal; the method further comprising: - activating the receive mode in at least one further antenna element of the array, proximate to the first antenna element, such that the second antenna element and each of the further antenna elements operate in receive mode while the first antenna element operates in transmit mode; the method being characterised by the following steps: - determining the relative phase and/or amplitude between the second antenna element and each of the further antenna elements; and/or - activating the transmit mode in at least one further antenna element of the array, proximate to the second antenna element, such that the first antenna element and each of the further antenna elements operate in transmit mode while the second antenna element operates in receive mode; and - determining the relative phase and/or amplitude between the first antenna element and each of the further antenna elements. - activating the receive mode in at least one further antenna element of the array, proximate to the first antenna element, such that the second antenna element and each of the further antenna elements operate in receive mode while the first antenna element operates in transmit mode; the method being characterised by the following steps: - determining the relative phase and/or amplitude between the second antenna element and each of the further antenna elements; and/or - activating the transmit mode in at least one further antenna element of the array, proximate to the second antenna element, such that the first antenna element and each of the further antenna elements operate in transmit mode while the second antenna element operates in receive mode; and - determining the relative phase and/or amplitude between the first antenna element and each of the further antenna elements. - determining the relative phase and/or amplitude between the second antenna element and each of the further antenna elements; and/or - activating the transmit mode in at least one further antenna element of the array, proximate to the second antenna element, such that the first antenna element and each of the further antenna elements operate in transmit mode while the second antenna element operates in receive mode; and - determining the relative phase and/or amplitude between the first antenna element and each of the further antenna elements.