The system of resonant transverse slots of equal length on the basis of a rectangular waveguide slow-wave structure and short-circuiting plunger at the waveguide end is considered in the paper. Slow-wave structure formed as a dielectric layer arranged parallel to the broad wall of the waveguide. It is shown that such a system can be configured for maximum radiation at the resonant frequency by optimizing of such parameters as distance from the short-circuiting plunger and the length of the slots in the array. The usage of the slow-wave structure in waveguide results in radiation pattern of the antenna array without any higher order interference maxima.