An electronically scanned slotted waveguide antenna radiates an RF signal as a scannable beam. The antenna has radiation waveguides positioned in an array. Radiation slots in the radiation waveguides radiate the scannable beam. A feed waveguide is coupled to the radiation waveguides. The feed waveguide feeds the RF signal to the radiation waveguides through coupling slots. The feed waveguide has sidewalls with tunable electromagnetic crystal (EMXT) structures thereon. The EMXT structures vary the phase of the RF signal in the feed waveguide to scan the radiated beam in one dimension. The radiation waveguides may also have tunable EMXT structures on the sidewalls to vary the phase of the RF signal to scan the radiated beam in a second dimension. The EMXT structures may be discrete EMXT devices or a EMXT material layer covering the feed and radiation waveguide sidewalls.