A calibration module for a tester, for testing a device under test, includes a pair of RF-channel terminals, a calibration device, a pair of measurement terminals and a mode selector. The pair of RF-channels terminals is configured to send or receive measurement signals to or from an RF-channel of the tester. The calibration device is configured to perform a calibration of the RF-channel based on the measurement signals sent to, or received from, the RF-channel. The pair of measurement terminals is configured to send or receive measurement signals to or from the device under test. The mode selector is configured to connect, in a calibration phase, the pair or RF-channel terminals to the calibration device for calibrating the RF-channel and to connect, in a measurement phase, the pair of RF-channel terminals to the pair of measurement terminals for routing measurement signals from the RF-channel to the device under test or vice versa.