Higher order mode coupling effects in the feeding waveguide of a planar slot array

The effect of internal higher order modes in the feeding waveguide of a planar slot array is investigated. Both the centered-inclined coupling slot and the longitudinal-transverse coupling slot are considered. Method of moments solutions to pertinent coupled integral equations are investigated for arrays of coupling slots of the centered-inclined and longitudinal-transverse types between a main waveguide and crossed branch waveguides. It is demonstrated that, by including the TE₂₀ mode coupling in the analysis, most of the higher order mode effects can be accounted for in reduced height waveguides, whereas in waveguides of standard height there may be a small additional effect arising from the TE₀₁ mode coupling.