The asymptotic radiation field and proper propagation mode spectra of the open planar waveguide

The radiation field of the asymmetric planar dielectric waveguide is evaluated using the steepest-descent method for both TE and TM excitations.; Continuous spectrum currents/fields of integrated open waveguide structures has been until recently neither conceptualized theoretically nor quantified numerically. That spectrum can be identified as the branch cut contribution to singularity expansion of those currents/fields in the complex axial transform plane. Singularities in that plane include poles associated with the guiding structure and branch points contributed by layered background environments. The manner in which singularities in background environments manifest themselves as branch points in the complex axial transform plane is reviewed.; Based on transform domain integral equation formulation, approximate and analytical expression for spectral domain microstrip current is obtained. The delta-gap feed model is exploited. That approximation is based on Maxwellian distribution for the transverse current profile. The spectral domain current is inverted into space domain by integration contour deformation in the top sheet of the axial transform plane. This result is the representation of currents in terms of proper propagation mode spectra. That spectra consist of bound propagation modes associated with pole singularities and continuous spectrum associated with integration around branch cuts contributed by background environments. During integration around branch cuts, singularities in the transverse transform plane migrate in a complicated manner. The trajectories of this migration are identified and suitably accommodated during the real axis integration in that plane. This overall procedure leads to a decomposition of the total currents into bound modes and continuous spectrum contributions. This representation is validated by real axis integration in the axial transform plane. Similar analysis leads to near and moderate zone electric fields of the guiding structure. The quasi TEM characteristic impedance of bound mode is calculated.; Numerical results are obtained, which compare bound mode and continuous spectrum contribution to microstrip currents. It is found that current is dominated by that of bound mode. The characteristic impedance of bound mode is validated by comparison with well-known empirical formula. The continuous spectrum current is maximal near feed point and decays rapidly with axial distant from the feed. The near field is dominated by continuous spectrum contribution. The extensive numerical results for near and moderate zone fields are obtained.; Asymptotic approximation to the field of an open integrated microstrip waveguide is achieved theoretically using the steepest-descent method (saddle point approximation). It is observed that the far zone cover field decays algebraically as r−(α+3/2) (α ≠ 0) transversely. The algebraic decaying factor α still remains to be determined in future research.