Some specific electrical properties of a waveguide-slot phase shifter have been studied in the paper. We propose to use waveguide-slot phase shifter as a controlled coupler in the switchgears of phased arrays with series feeding and p–i–n-diodes control. The characteristics of the waves transmitted through the waveguide and their dependences on the slot’s position and dimensions were considered. The slot of special form was cut through the waveguide wide wall. We succeeded in obtaining the phase shift up to 360 degrees by the lengthwise variation in the slot’s position in a coupling window and by the slot’s displacement specularly relative to the waveguide’s axis line. The study of the problem was conducted experimentally and by simulation technique. The simulation results were verified by experimental data. The proposed phase-shifter can be also used in switchgears of phased arrays with a locked beam.