DISCRETE HIGHER-ORDER LEAKY-WAVE MODES AND THE CONTINUOUS-SPECTRUM OFSTRIPLINE

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.