Dp. Nyquist et Dj. Infante, DISCRETE HIGHER-ORDER LEAKY-WAVE MODES AND THE CONTINUOUS-SPECTRUM OFSTRIPLINE, IEICE transactions on electronics, E78C(10), 1995, pp. 1331-1338
Discrete higher-order modes of stripline, both proper and leaky, as we
ll as its continuous spectrum are conceptualized and quantified by a f
ull-wave integral operator formulation through complex analysis in the
axial Fourier-transform plane. Poles associated with the parallel-pla
te background environment lead to branch points in the axial transform
plane. A criterion for choice of associated branch cuts to restrict t
he migration of poles in the transverse transform plane is identified.
The higher-order discrete modes are both bound (proper), with a low-f
requency cutoff, and leaky (improper). The highest-order proper mode h
as a propagation constant very nearly equal to that for the TM paralle
l-plate mode. Distributions of the continuous-spectrum currents appear
to consist of a smooth transition from those of the highest propagati
ng proper discrete mode, as might be expected physically. The continuo
us spectrum is dominated by the propagating portions associated with a
ny TM background modes (poles) which are above cutoff, and in fact by
spectral points in a region very near to the branch point.