A multiple input multiple output (MIMO) calibration device (360) for calibrating a phase relationship between at least two signals present on at least two radio frequency (RF) paths coupling a wireless communication unit and the MIMO calibration device (360) is described. The MIMO calibration device (360) is operably coupleable via at least two RF paths between a wireless communication unit and an antenna arrangement (219). The calibration device (360) comprises a processing module (490) configured to: process a coupled amount of at least one first signal from a first path operably coupleable to a first polarization of the antenna arrangement (219) to determine at least one pilot signal from said at least one first signal; process a coupled amount of at least one second signal from a second path operably coupleable to at least one second polarization feed of antenna arrangement (219), different to the first polarization, to determine the at least one pilot signal from said at least one second signal; and determine a first phase relationship of the same pilot signal between the at least two RF paths.