Embodiments of an apparatus of a user equipment (UE) configured for operation in a fifth-generation system (5GS) are described herein. The UE comprises first and second array antennas for transmission of mmWave signals including a sounding-reference signal (SRS). In response to decoding radio-resource configuration (RRC) signalling that indicates antenna switching for SRS, the UE initiates a countdown timer and transitions the second array antenna from a low-power state to an active state. If a downlink control information (DCI) indicating SRS antenna switching is not received while the countdown timer is active, the UE generates a command to transition the second array antenna to a low-power state upon expiration of the countdown timer.