Limitations on directional patterns of phase-compensated circular arrays

This paper studies the principal design parameters of phase compensated circular arrays with a view to the synthesis of diametricplane directional patterns having low side-lobes. After summarizing the general properties of such arrays it is shown that a maximum inter-element spacing exists, which if exceeded results in a rapid increase of sde-lobe level. In most cases this spacing is 0.45¿. The effects of both amplitude tapers and directional elements are studied and it is shown that neither smooth amplitude tapers nor the use of directional elements can alone produce very low side-lobes. Several possible approaches to the design of low side-lobe aerials are discussed, involving tapers, directional elements, multiple rings, and semi-circular arrays. Experimental results are presented for the measured directional pattern of a 16-element circular array operating at 427 Mc/s under various conditions of excitation, and the results show sensible agreement with theoretical predictions. The studies are concerned with the possible application of these arrays to radar systems with 360 deg electronic scanning. Such systems place engineering constraints on the design of the arrays; consequently the effect of such constraints on pattern synthesis is also considered.