Dr. Jackson et al., An excitation theory for bound modes, leaky modes, and residual-wave currents on stripline structures, RADIO SCI, 35(2), 2000, pp. 495-510
The nature of the current on a general multilayered printed-circuit stripli
ne structure excited by a delta-gap source is investigated. The current is
obtained through the construction of a semianalytical three-dimensional (3-
D) Green's function, which accounts for the presence of the infinite conduc
ting strip and the layered background structure. The 3-D Green's function i
s obtained by Fourier transforming the delta-gap source in the longitudinal
(z) direction, which effectively resolves the 3-D problem of a delta-gap s
ource into a superposition of 2-D problems, each of which is infinite in th
e z direction. The analysis allows for a convenient decomposition of the st
rip current into a sum of constituent parts. In particular, the strip curre
nt is first resolved into a set of bound-mode current waves and a continuou
s-spectrum current. The continuous-spectrum current is then represented as
a set of physical leaky-mode currents in addition to a set of "residual-wav
e" currents, which arise from the steepest-descent integration paths. An as
ymptotic analysis reveals that the residual-wave currents decay algebraical
ly as z(-3/2). Far away from the source, the residual-wave currents dominat
e the continuous-spectrum strip current. Results are shown for a specific t
ype of stripline structure, but the analysis and conclusions are valid for
arbitrary multilayer stripline structures.