INTEGRAL-REPRESENTATION OF SPATIAL GREENS-FUNCTION AND SPECTRAL-DOMAIN ANALYSIS OF LEAKY COVERED STRIP-LIKE LINES

This paper studies the possible integral representations of the Spatia l Dyadic Green's Function of a laterally open but covered multilayered planar waveguide with translation symmetry. Among all of integral rep resentations, we especially focus on that unique representation which comprises only outgoing waves (energy transferred from the source to i nfinity in case lateral radiation was present). We propose this specif ic integral representation as the most appropriate in the Spectral Dom ain Analysis of strip-like structures when these are assumed to be gui ding/leaky systems with translation symmetry. This integral representa tion directly provides the integration contour to be used in the defin ition of the inverse Fourier transform. Some aspects concerning the us e of the nonconventional Fourier transform are discussed in connection with the application of the Method of Moments. It is also highlighted that the dispersion relation of the strip-like configuration is expre ssed in terms of the zeros of a multivalued complex function. This fac t becomes relevant when searching for zeros out of the spectral sheet (i.e., zeros associated with leaky modes). Finally, some numerical res ults are presented. These computed values show good agreement when com pared with some previously published data. The influence of different definitions of the inverse integration contour on the propagation char acteristics of a pair of coplanar coupled strips is also investigated. Computed data will show the leakage characteristics of a pair of nonc oplanar strips.