The radiation pattern and reactance vales, of an ESPAR (electronically steerable passive array radiator) antenna composed with 7 elements, converged by adopting a steepest gradient method to an equivalent weight vector of corresponding structure are investigated. The converged beam direction and reactance values have a tendency to be biased whereas those of null are continuously changed. The same tendency appears also to experimental results. The tendency remains even if the variable reactance range is enlarged. Reactance range not to limit the convergence of forming a beam or a null is presented. The beamforming capability is studied by comparing directivity and current distribution with those of an ordinal phased array antenna that has the same element's arrangement. It is shown that ESPAR antenna has almost the same ability to suppress two interference waves as an ordinal phased array, if the is no limit to the variable reactance range.
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