EXCITATION OF LEAKY MODES ON MULTILAYER STRIPLINE STRUCTURES

A quasi-analytical method for calculating the excitation of leaky mode s on multilayer stripline structures by a finite source is presented i n this paper. Simple sources such as an infinitesimal dipole near the conducting strip or a delta-gap feed on the conducting strip of the tr ansmission line are considered, The method uses a numerically construc ted Green's function for the source in the presence of the conducting strip, which is calculated from Fourier transform theory in terms of a one-dimensional Green's function for a line source in the presence of the conducting strip. The numerical Green's function involves a one-d imensional integration in the longitudinal wavenumber plane, The resid ue contributions from the poles of the Green's function define the exc itation amplitudes of the leaky and bound modes that exist on the stru cture. The numerical Green's function is also used to numerically calc ulate the complete current on the strip excited by the source. The cor relation between the leaky-mode current and the complete current is us ed to define the extent of the physical meaning of the leaky mode, The generalized pencil of functions (GPOF) method is used to study this c orrelation by resolving the complete current on the strip into exponen tial waves, which are then compared with the current of the leaky mode . The physical meaning of the leaky modes is also analytically examine d by consideration of the branch cuts in the longitudinal wavenumber p lane for the numerical Green's function integration, A ''path consiste ncy condition'' is established as a necessary condition for the physic al meaning of the leaky mode.