An antenna system for shared operation has three antenna stacks each with two mutually orthogonal polarisations (+45 degree and −45 degree). It is for use with multiple base stations. It combines on to a single feeder signals associated with like polarisation and with the base stations, and separates on to different feeders signals associated with different polarisations. This applies both to transmit and receive signals passing between antennas and base stations. Signal combining is achieved by band pass filtering. Each base station transmits and receives via a respective antenna stack, and so each can have an individual angle of electrical tilt. Two, three or four feeders may be used to route signals between antennas and base stations. With four feeders, transmit and receive signals and differing polarisation associations are separable, reducing intermodulation products. With two feeders, transmit and receive signals with like polarisation associations are combined.