Mounting a shielded antenna unit inside a building

A method of mounting an antenna unit comprises locating the antenna unit, consisting of an antenna 11 inside a shielded housing 10, inside a building 32 so that the antenna unit may transmit and receive signals to and from the outside the building through an unshielded part of the housing and so that the shielding prevents leakage of signals from the antenna into the building. The housing may be permanently or removably attached to a window 26 or vent in the building and further shielding may be provided around the attachment area (Figures 2 to 4). The shielding means may be shaped so as to conform to both the antenna radiation pattern and the housing shape (figures 2 to 4) and may be formed of layers of conductive foam (12a, Figure 2 and 4) and aluminium foil (12b, Figures 2 and 4). The antenna unit may be attached to a base station transceiver 6 in a mobile telecommunications network. Another embodiment is arranged to fit in a corner window (Figure 6) and the invention enables antenna units to be placed in listed or protected buildings.