Discrete Higher-Order Leaky-Wave Modes and the Continuous Spectrum of Stripline

Dennis P. NYQUIST  David J. INFANTE  

IEICE TRANSACTIONS on Electronics   Vol.E78-C   No.10   pp.1331-1338
Publication Date: 1995/10/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Special Issue on Electromagnetic Theory)
stripline,  modes,  discrete,  higher,  leaky,  continuous,  

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Discrete higher-order modes of stripline, both proper and leaky, as well as its continuous spectrum are conceptualized and quantified by a full-wave integral operator formulation through complex analysis in the axial Fourier-transform plane. Poles associated with the parallel-plate background environment lead to branch points in the axial transform plane. A criterion for choice of associated branch cuts to restrict the migration of poles in the transverse transform plane is identified. The higher-order discrete modes are both bound (proper), with a low-frequency cutoff, and leaky (improper). The higher-order proper mode has a propagation constant very nearly equal to that for the TM parallel-plate mode. Distributions of the continuous-spectrum currents appear to consist of a smooth transition from those of the highest propagating proper discrete mode, as might be expected physically. The continuous spectrum is dominated by the propagating portions associated with any TM background modes (poles) which are above cutoff, and in fact by spectral points in a region very near to the branch point.