Manipulation of Characteristic Wave Modes

The influence of the antenna impedance loading on the characteristic wave modes is investigated and evaluated. It is shown that the eigenvalue behavior of the characteristic modes can be modified by impedance loading at specific positions on the antenna. Thereby, it is possible to manipulate certain modes such that they resonate in the desired frequency band. These modes can then effectively be excited to achieve the desired antenna perfor- mance. It is found that using characteristic wave modes leads to better intuitive insight compared to the entire current distribution. Furthermore, we present a definition of the modal efficiency of the characteristic modes, which can be used to take into account the effect of losses in the matching components or the load elements. Index Terms—Antenna theory, eigenvalues and eigen-functions, impedance loading.