Directive couplers in wave guides

Different modes of coupling two wave guides, in particular their directive properties, are investigated. An r.f. unit using a directive coupler is described. Directive couplers are also used in standing-wave measuring equipment, power monitoring, etc. In the first part of the paper formulae derived by H. A. Bethe are applied to different wave-guide configurations, such as two parallel or crossed wave guides, using circular holes or linear slots as coupling elements. Formulae giving the directivity and the attenuation between guides are derived, and numerical examples are worked out, for all the cases considered. In the second part broad-banding of directive couplers by multiplication of coupling elements (holes, slots, etc.) is considered. The formulae can be applied to end-fire or broadside arrays. The third and last part is devoted to a discussion on the experimental results obtained with directive couplings. The importance of the accuracy of mechanical work, perfect matching of the excited waveguide and the effect of the finite size of the coupling elements are discussed.