On the Independence of the Excitation of Complex Modes in Isotropic Structures

We investigate the independence of the excitation of complex modes in lossless and isotropic structures. We clarify some of the ideas in literature regarding the excitation of complex mode pairs. In particular, we show in this work that it is practically possible to independently control the excitation amplitude of an individual mode in a pair of conjugate complex modes. Theoretical clarification of the claim that such modes in a complex pair must be excited with equal amplitudes, as suggested by some authors, is also provided. The eigenmodes of a coupler comprising a regular forward-wave and a metamaterial backward-wave or negative-refractive-index transmission-line (NRI-TL) provides a representative platform to investigate our assertions which are verified using a commercial microwave circuit simulator.