On the shaping of the main lobe in wide-band arrays

This paper describes a method to obtain a wide-band beam pattern whose main lobe has the desired shape and, at the same time, the level of the side lobes is acceptable. The aim is to reproduce a main lobe profile as close as possible to the desired one through the synthesis of the array-weighting window. A typical goal is to obtain, in wide-band conditions, a flat-top shaped beam similar to the ones produced by specific narrow-band windows. To achieve this result, an optimization process based on simulated annealing is developed and applied under different operating conditions, including two wide-band beam pattern definitions and different values of the fractional bandwidth. Although the shape of the resulting main lobe is not as good as the one obtained in narrow-band conditions (the reasons for this drawback are given), it is shown that the adoption of windows synthesized by the proposed method is more suitable than the direct application of narrow-band windows in wide-band conditions. In addition to providing better performances, it is shown that the windows synthesized by the proposed method also result in greater robustness to random perturbations of weight values, which are unavoidable in real systems.