METAL MESH COUPLERS USING EVANESCENT WAVES AT MILLIMETER AND SUBMILLIMETER WAVELENGTHS

A metal mesh coupler, which makes use of the evanescent-wave coupling between a metal mesh and a dielectric plate, has been developed as a q uasi-optical component for millimeter and submillimeter wavelengths. T he transmission properties of this type of coupler are investigated ex perimentally and theoretically at the millimeter-wave frequencies. The transmittance of the evanescent-wave coupler with a capacitive metal mesh can be adjusted by more than 70 percent by altering the spacing b etween the capacitive mesh and the silicon plate by less than lambda/1 40 at 56 GHz. The experimental and theoretical results show that large and rapid variations of transmittance in the coupler arise from chang es in the effective refractive index of the silicon plate due to the e vanescent-wave coupling effect. An equivalent circuit for the evanesce nt-wave couplers is developed for use in the design of coupler configu ration. (C) 1998 Scripta Technica.