Spectral analysis considerations relevant to radiation and leaky modes of open-boundary microstrip transmission line

Abstract

The continuous radiation spectrum of an open microstrip transmission line and its nonspectral leaky modes are conceptualized through a transform-domain integral-operator formulation and relevant spectral analysis. The radiation spectrum is identified with branch cuts in the axial wavenumber plane, which constrain the migration of branch-point singularities in the transverse wavenumber plane. Leaky-wave modes occur only when the branch cuts in the axial wavenumber plane are violated. The relationship among spectral radiation modes, nonspectral leaky-wave modes, and branch cuts in the axial wavenumber plane is discussed. The influence of branch cuts in the axial wavenumber plane upon the location of branch points in the transverse wavenumber plane is detailed, and a rationale is offered for the choice branch cuts in the latter plane. The formulation is applicable to a wide class of open conducting or dielectric waveguides. >