Effects of actual antenna excitation on natural radiation modes

In this paper, by using the Theory of characteristic modes (TCM), we analyze the effect of Inductive Coupled Elements (ICE's) used for the excitation of Characteristic Modes (CM) on antenna chassis. ICE's are used in sets to excite chassis modes and are placed at current maximas of the desired modes. Using TCM analysis, it was found that the introduction of such ICEs significantly affect the CM of the chassis and therefore can not be used as an efficient method for the excitation of CM. In addition, CM are compared with the total current generated on the surface and vicinity of a PIFA antenna. For normal excitation (not taking into account a single CM), a combination of modes are excited on the antenna chassis and surface depending on the frequency of interest. Also these currents are localized around the antenna.