Abstract: A loop directional RF coupler between a waveguide and coaxial line maintains a high degree of directivity while providing substantially improved coupling values. A conductive loop assembly terminating the coaxial line is accepted into an aperture means defining an aperture in one wall of the waveguide section of the coupler. The aperture is greater in diameter than the largest transverse dimension of the loop, or of the loop assembly. A capacitive or inductive conductive obstacle is affixed to an interior wall of the waveguide section adjacent the aperture. A second conductive obstacle is positioned downstream of the first obstacle to compensate any mismatch.