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The effect of broadband signals on the far-zone field of long arrays is investigated in terms of the energy radiation pattern. A generalized directive gain is introduced which depends on the signal spectrum. With maximum directivity as a criterion it is shown that the problem of optimizing a long isotropic array with respect to a given signal can be associated with a classical eigenvalue problem. The concept of array-bandwidth is introduced. Computed curves for directivity and directive gain are given in terms of this parameter and signal bandwidth. It is shown that while little improvement in directivity is achieved by optimizing the distribution coefficients of an array, a substantial reduction in sidelobe level is obtained when the signal bandwidth is comparable to the array bandwidth.