A hybrid tracking algorithm for characteristic mode analysis

Characteristic mode analysis (CMA) is a useful design tool that enables antenna designers to follow a systematic approach for extracting the radiating properties of a structure. These properties are quantified with CMA in the form of eigenvalues and eigenvectors, i.e., the solutions of a generalised eigenvalue equation that is formulated from the Method-of-Moments (MoM) impedance matrix. One particular challenge to CMA, however, is the manner in which quantities such as eigenvalues are plotted as a function of frequency. At each discrete frequency sample, the eigenvalues are sorted according to modal significance, i.e., based on the efficiency with which they radiate. At higher frequencies, the ordering of modes may differ from that obtained at lower frequencies. A tracking algorithm will be introduced that keeps the ordering of modes as consistent as possible over frequency. The method presented is an extension of that done in [1], where a linear correlation is applied to the characteristic currents between adjacent frequency increments to obtain a ranking vector. This new hybrid technique is based on extrapolating the eigenvalue and characteristic angle curves and then applying linear correlation between the characteristic currents where needed to verify a successful mapping.