The calculation and the measurement of the coupling properties of dielectric image lines of rectangular cross sections

The calculation of the coupling properties is based on the exact solution of the eigenvalue problem of coupled dielectric image lines reported by Solbach and Wolff (1978). Attention is given to the cross section of coupled dielectric image lines, a uniform coupling section of coupled dielectric image lines, the normalized coupling length for total power transfer versus the normalized frequency for low-permittivity lines, and the directional coupler structure. It is shown that it is possible to calculate the coupling properties of uniform coupled dielectric image lines and directional couplers on the basis of dielectric image lines at reasonable accuracy. Some design features for directional coupler structures are also discussed.