A special class of multiple aperture couplers is used in terrestrial m
icrowave radio to provide mode diversity protection to mitigate effect
s of multipath fading. In these couplers, one of the waveguides is ove
rmoded and specific modes are extracted from this waveguide to a small
er waveguide through a set of circular apertures without affecting oth
er propagating modes, A comprehensive analytical method applicable to
both horizontal and vertical multi-aperture couplers is presented. The
analysis, design and measured results for a horizontal mode coupler a
re discussed.