A. Takasugi et al., A SURFACE-MOUNTABLE CERAMIC 3-DB DIRECTIONAL COUPLER, Electronics & communications in Japan. Part 2, Electronics, 77(4), 1994, pp. 51-57
In the lossless symmetric reciprocal four port represented by the dire
ctional coupler, it is possible to calculate an invariant from the mea
sured results of the s parameters. As a result, an integrated directio
nal coupler was fabricated with high-permittivity ceramic waveguide (D
EW: dielectric E-plane waveguide) and a coupling of 3 dB was obtained.