According to the present disclosure there is provided a multiple-input-multiple-output (MIMO) transmitter for transmitting wireless communication signals over a communication channel to a receiver, the transmitter including a digital signal processor configured to perform pre-coding on a plurality Ns of data streams; a plurality NRF of radio-frequency (RF) chains each configured to pass a pre-coded data stream from the digital signal processor to generate a signal representing that data stream; a lens antenna array comprising an array of NT antenna elements; and a selecting unit coupled between the plurality NRF of RF chains and the lens antenna array, the selecting unit including a plurality of separate coupling units each configured to couple a respective RF chain to a selective sub-array of NTBRF antenna elements concurrently for transmitting the signal representing the data stream passed through that RF chain.