The invention relates to a method and a WCDMA radio system implementing the method wherein a connection between terminal devices and a base transceiver station is ensured by changing the transmission mode of a signal from a beamforming mode to a single antenna mode in a situation wherein calibration of an antenna array of the base transceiver station resides below a threshold value describing the quality of the calibration. The method comprises determining, at the base transceiver station, a calibration quality indicator describing the quality of calibration of the antenna array; checking whether the determined calibration quality indicator resides below a calibration quality threshold value, the calibration quality threshold value being a predetermined value; and switching over to using an antenna element specific transmission when the calibration quality indicator resides below the calibration quality threshold value.