A data transmission unit includes a transmit unit and a receive unit. The transmit unit and the receive unit are relatively movable with respect to another of the receive unit and the transmit unit. The data transmission unit further includes a coupler, the receive unit being configured to receive data from the transmit unit via the coupler even during a relative movement between transmit unit and receive unit. The coupler includes a first dielectric waveguide including a conductor body and a retaining structure.
