. In the article, the external parameters of the connection of a rectangular waveguide partially filled of linear dielectric with a rectangular waveguide partially filled of a nonlinear dielectric are determined. Knowledge of the external parameters of such a connection ensures the design of devices with open nonlinear elements. Promising microwave paths of radio engineering systems based on rectangular waveguides partially filled of dielectric include a wide variety of active and passive microwave devices. The plane-transverse junction of these waveguides is considered for various geometric dimensions of dielectric plates and their relative permittivity. Such a junction is characterized by reactive conductivity, which is determined through the sum of the reactive conductivities of local fields. The transverse electric field at the junction is represented through the eigenvector function of the geometric surface, which coincides with the cross section of the waveguides. The scattering matrix of the plane-transverse junction is determined through the conductivity of the sections of the two waveguides and the conductivity of the plane-transverse junction. The dependences of the traveling wave coefficient and the modulus of the reflection coefficient on the geometric dimensions of the dielectric plate are plotted taking into account the local fields generated at the plane transverse junction. At the junction of two waveguides, not only changed the geometric dimensions of the dielectric plates along the wide and narrow walls of the waveguide, but also their relative permittivity. In one case, two higher types of waves were taken into account: quasi - H30 and quasi - H12, in the other case - four higher types of waves: quasi - H30, quasi - H12, quasi - E12, quasi - H50. Calculations show that an increase in the number of higher types of waves has practically no effect on the accuracy of calculations. The results obtained indicate the rapid internal convergence of the obtained solutions and the correct choice of the transverse electric eigenvector function of rectangular waveguides partially filled of dielectric as approximate the field on the junction of two waveguides.