This article presents an optimization immune algorithm (opt-IA) for null steering of linear antenna arrays by controlling only the element amplitudes. Nulling of the pattern is also achieved by controlling the phase-only and the complex weights (both the amplitude and phase) of the array elements. The opt-IA is a new evolutionary computing algorithm based on the clonal selection principle of immune system. To show the accuracy and flexibility of the proposed opt-IA, several examples of Chebyshev array pattern with the imposed single, multiple, and broad nulls are given. It is found that the nulling technique based on opt-IA is capable of steering the array nulls precisely to the undesired interference directions. (c) 2008 Wiley Periodicals, Inc.