Characteristic Aperture Modes for the Mutual Coupling Analysis in Finite Arrays of Aperture-Coupled Antennas

Calculation of mutual coupling in finite arrays of aperture-coupled antennas with an arbitrarily shaped aperture is seriously impeded by the number of unknowns necessary to describe the aperture field. Entire domain expansion functions are extracted numerically from the equation tha has to be satisfied by the equivalent magnetic current on the aperture of asingle antenna element by applying the well developed theory of Characteristic Modes. The resulting weighted eigenvalue equation gives an orthogonal set of eigenmodes which can be ordered according to their contribution in therealpower flow through the aperture. It is shown, that even for ‘near field’ quantities like S-parameters, only a limited number of characteristic modes is sufficient to characterize the electromagnetic coupling through the aperture. The procedure was used in a methodof moments code and results are compared to measurements and other calculations from literature.