Circular arrays - Their properties and potential applications

The paper reviews the properties of circular arrays and shows that for directional beam patterns, there are two principal forms of array excitation. The first, known as beam cophasal excitation, causes the contributions from all the elements to add coherently together in one (main beam) direction. This can offer broad band performance but, in general, suffers from high sidelobes and mutual coupling effects, unless the excitation is restricted to about 120 degrees of arc. The second approach involves separate excitation of independent spatial harmonics of the far field pattern by means of a suitable feed network. This can offer wide bandwidth (constant beamwidth) performance plus the ability to compensate for mutual coupling effects. The latter properties seem particularly suitable for application to wide bandwidth communication arrays, direction finding systems and null steering. The ability to compensate for mutual coupling also looks useful for applications involving very small radius arrays.