The effects of mechanical tolerances on multi-aperture waveguide directional couplers

Mechanical tolerances of the coupling apertures in a 8 mm multi-aperture waveguide directional coupler (MAWDC) introduced by the manufacturing process lead to a variation in the device performance such as the directivity and the coupling value. To obtain this variation by repeated experiments of large numbers of randomly perturbed geometries is excessively costly. An alternative is to find the changing rule of the performance with respect to each geometric variable. It is cheaply available over the whole frequency band when the appropriate theory of coupling by apertures is used for the analysis. In this study, an accurately designed millimetre wave MAWDC working from 26.5 GHz to 40 GHz is fabricated. By contrast with the original designed coupler, a series of coupling walls with different dimension tolerances and position tolerances from 0.05 mm to 0.2 mm in the apertures are manufactured. Results are presented when these coupling apertures have different tolerances. The changing rules of the performance are also obtained.