Abstract: In a waveguide structure, there is provided a waveguide section rotatable about its longitudinal axis and an electric DC stepper motor arrangement. The rotor of such an arrangement is constituted by magnetic returns fixedly mounted on the waveguide section, and has a rotation axis which coincides with the longitudinal axis of the section. The rotor is therefore rotatable with the waveguide section about the longitudinal axis of the same. The motor arrangement further includes a stator provided with a plurality of poles which cooperate with the magnetic returns to rotate the waveguide section so as to adjust as desired its angular position. When the waveguide section has a circular cross section and is provided with two diametrically opposed lines of tuning screws, the waveguide structure forms a microwave polarizer which can be used in a variable power combiner.