A slot array antenna includes a waveguide slot body and a dielectric slab. The waveguide body includes one or more walls that define a waveguide aperture, the waveguide aperture extending along a longitudinal axis of the waveguide slot body. The waveguide slot body includes a plurality of slots disposed on one or more walls of the waveguide slot body. The dielectric slab is disposed within the waveguide aperture and extends along the longitudinal axis of the waveguide slot body. The dielectric slab is rotatable about the longitudinal axis within the waveguide aperture.