Impact of capacitive coupling element design on antenna bandwidth

A coupling element is typically used to excite one of more characteristic modes of a structure to form some desired radiation properties. In particular, non-resonant coupling elements (CEs) are attractive, since it is electrically small and can be more conveniently integrated into the structure, such as the chassis of a mobile terminal. In this case, the chassis is the primary radiator of the mobile terminal. However, there is still limited knowledge on how to design and
optimize coupling elements. In this paper, we examine how the dimensions of a single capacitive coupling element (CCE) influence the potential bandwidth of exciting the fundamental dipole mode of a rectangular terminal chassis. The parametric study shows that the CCE must not be too small electrically, for the sake of bandwidth. However, the bandwidth saturates when the size of the CCE is increased beyond a certain threshold. Therefore, this study provides some useful insights and guidelines for CCE design.