A numerical consideration is performed on degradation of element properties and array patterns of a planar phased array owing to the effects of antenna element structure. By using a crossed 3‐subelement Yagi antenna specially designed for the VHP‐band MST radar in Japan (the MU radar) as a model of antenna element, the following two subjects are investigated: (1) mutual coupling effects induced by deviation of the intersecting point of a pair of crossed subelements from each subelement center, and (2) effects of vertical current which flows on the mast supporting the antenna subelements. It is concluded that neither of them provide significant degradation of either element properties or array patterns. Although this conclusion is derived for specific phased arrays composed of specific antenna elements, it will be essentially valid for ordinary planar phased arrays composed of dipoles or Yagi anten