The generation of antenna characteristic modes from the impedance matrix using the moment method

The theory of characteristic modes enables the current distribution and hence the radiation characteristics of structures to be expressed as an infinite set of mathematical basis functions. This set of functions is uniquely defined by the structure´s dimensions and frequency of operation and it is independent of any particular excitation. The authors describe a procedure for the computation of the characteristic modes of arbitrary antenna geometries using a readily available moment method code. The reliance of the characteristic modes on the wire segmentation scheme used is investigated along with the number of significant modes that need to be summed to obtain accurate pattern and impedance data. Finally, characteristic modes are used as an aid to understand the experimental impedance data from a particular antenna and transmission line configuration