Introduction

The characteristic mode (CM) theory is a relatively new topic in the antenna community. The great potential of the CM theory in antenna engineering has not been widely recognized until 2000. In this chapter, several well‐known modal analysis methods for particular antenna problems are reviewed first. It helps the readers have a preliminary knowledge about what modal analysis talks about. It also illustratively shows how these modal analysis methods can help in practical antenna design. Next, we address the fundamental question: why the characteristic modes were proposed and what are characteristic modes? The primary features of the CMs are then followed. A history review for developments and applications of the CM theory in antenna engineering are also presented. Finally, we briefly introduce many CM variants for different radiation/scattering structures and materials. The details of these CM variants will be described in Chapters , , , .