High Performance Ridge Waveguide Directional Couplers

Abstract

Ridge waveguides are used in microwave transmission systems where broadband performance, associated with low attenuation and high power capabilities, are required. In addition, this technique is also used for various special components such as cavities, mixers, etc. Design proposals exist for single and double ridge waveguides with bandwidths of 2.4 : 1 and 3.6 : 1. Because of their simpler design, single ridge waveguides are mostly used for components such as directional couplers, filters, etc., while double ridge waveguides are usually restored to for longer transmission lines. The quality of ridge waveguide components available on the market is considerably lower than that of components in standard rectangular waveguide technique. The reflection coefficients even for simple elements such as bends, twists, straight sections, have values of r = 0.03 to 0.2 (VSWR 1.06 to 1.5). This is mainly due to the lack of suitable measuring devices during the development of such components. This has been the main reason for the design of new directional couplers with directivities D ≥ 40 dB for bandwidths of 2.4 : 1 and D ≥ 35 dB for bandwidths of 3.6 : 1. Conventional designs for coupling networks rmostly use λ/4 arrangements with corresponding matching networks at both ends. The disadvantages of such λ/4 arrangements are well known: The number of coupling holes over a given length is limited, and for coupling coefficients of 10 - 20 dB large hole diameters are required, which causes heavy field distortions and also second order effects.