TE-wave scattering and radiation from a slitted parallel-plate waveguide with rectangular grooves is considered. The Fourier transform and the mode matching are used to represent the scattered field in terms of the continuous and discrete modes. The simultaneous equations for the discrete modal coefficients are obtained by matching the boundary conditions. The fast-converging series solutions are presented to evaluate the far-zone radiation, reflection, and transmission coefficients. The numerical computations illustrate the angular behaviors of far-zone radiation in terms of the slit size, groove size, and operating frequency. The antenna radiation pattern of the slitted parallel-plate is measured and compared with the theory.