An analogue computer has been constructed to calculate the horizontal radiation patterns of aerial arrays comprising a number of radiating elements mounted on a central support mast. The radiation pattern of a single element must be known, and from this the pattern for a number of identical elements may have any desired amplitudes and phases. The principle used is the addition of a number of audio-frequency voltages, each component representing the radiation from one element in a particular direction. By using a bank of rotary switches, the appropriate summations are made in turn for bearings at intervals which may be either 7.51B 70 30 1B 73 or 151B 70 30 1B 73, the resultant being indicated on a meter. The computer may be adapted to other types of visual display.