Akademik Veri Yönetim Sistemi
JOURNAL OF ELECTROMAGNETIC WAVES AND APPLICATIONS, cilt.18, sa.6, ss.769-779, 2004 (SCI-Expanded)
A proof is provided for the fact that whenever there is a frequency region of a backward wave in metallic waveguides filled with media which do not induce coupling between transverse and longitudinal fields, then there exists an adjacent region with a complex propagation constant. This proof is based on the Method of Moments approach used in converting the problem of calculating the modal fields of the inhomogeneous and/or anisotropic waveguide, to a matrix eigenvalue problem. It is also shown that for those structures which are additionally frequency independent, a necessary condition for the existence of backward waves is that TE-TM modes of the empty waveguide whose eigenfunctions are used in the representation of the fields in application of the Method of Moments, be coupled. In other words the waveguide must be inhomogeneous or anisotropic or both for a backward wave mode to exist.