In this paper, to identify the dynamic characteristics of antenna system, the antenna is divided into 4 components and those were analyzed with a conventional FEM package MSC/NASTRAN. Using a Component Mode Synthesis Method, dynamic characteristics of total system is also identified. The Coherence of each component to total system is evaluated by using strain and kinetic component to total system is evaluated by using strain and kinetic energy. The improving strategy of dynamic characteristics is suggested by changing mass and stiffness of large coherence components.