On the interaction of Characteristic Modes in slot antennas etched on finite ground planes

Characteristic Mode (CM) analysis is carried out in order to understand the underlying physics of a popular slotted planar antenna, namely U-slot antenna, for achieving better performance. The Theory of Characteristic Modes (TCM) has been applied to get physical insight on the radiating behavior of the modes present on a U-slot etched on a finite metallic plate. Different types of U-slot planar structures are presented in order to demonstrate the effects produced by the inclusion of a U-slot in a broadband finite structure. The interaction between the corresponding U-slot modes and the metallic plate modes is fully discussed and justified for two specific cases. The information yielded by the modal analysis reveals the close influence of the plate size on the resonance frequency of the U-slot aperture. On the other hand, the length of the U-slot arms directly affects the resonance frequency of the modes associated to the metallic plate.