Characteristic mode analysis (CMA) is the numerical calculation of a weighted set of orthogonal current modes that are supported on a given structure. These modes depend only on the physical parameters of the structure, and do not depend on the way the structure is excited. Calculation of characteristic mode currents, and resulting radiation patterns and near fields, provide a deep insight into the physical behavior of the analyzed structure. This helps designers to follow a systematic, intelligent approach rather than a brute force method, by looking at the eigenvalue spectrum and the eigenvector distribution.
Characteristic mode analysis is performed by solving a particular eigenvalue equation, which is derived starting from the MoM impedance matrix. WIPL‑D software uses Higher Order Basis Functions (HOBFs) and quadrilateral mesh, which enable significant reduction of required number of unknown coefficients. This leads to very fast MoM matrix calculation and reduced number of unknowns in eigenvalue equation. Thanks to these facts, CMA Solver implemented in WIPL‑D software is very efficient.
By solving eigenvalue equation, eigenvalues and required number of corresponding eigenvectors are calculated. Starting from eigenvalues, we calculate modal significance and characteristic angle, as two very important parameters which give us insight into physical behavior of the observed modes. On the other side, starting from the eigenvectors we calculate characteristic mode currents as well as its radiation patterns and near field distribution. In order to provide that the modes with the same index number at different frequencies refer to the same physical modes, an advanced mode tracking technique is implemented into WIPL‐D CMA solver.
For more info, please check the following document.