Unequally-spaced, broad-band antenna arrays

Requirements for a broad-band, steerable linear antenna array are given. The limitations due to grating lobes of an equally-spaced array are discussed. Results are given of the study of several different unequally-spaced arrays which have two advantages: 1) fewer elements for comparable beamwidth; 2) grating lobes and minor lobes replaced by sidelobes of unequal amplitude which are all less than the main beam. A scheme for controlling the cosine arguments in the radiation pattern formula is given which has resulted in one of the best patterns of this study of unequally-spaced arrays. The universal pattern factor was computed for an array having a set of spacings determined by this scheme. This array is capable of steering a beam \pm90\deg over a 2-to-1 frequency band with no sidelobe above -5 db. It uses 21 elements, compared to 78 for an equally-spaced array of similar beamwidth. The results obtained indicate that further study of the controlled cosine method and unequal spacing in general should result in better pattern characteristics.