A mobile-radio base station for a teleconununicaions system includes vector modulator means for independently controlling the phase and/or amplitude of a plurality of component signals representative of the signal to be transmitted or received, such that when these signals pass through a plurality of antenna elements, a beam is formed in a direction according to the phase relationship of the component signals. The base station further includes interface means allowing other base stations to be coupled to the same antenna, with each base station having independent control of its beam direction.