The quasistatic characteristics of a parallel-plate waveguide with multiple slots of infinite extension in its upper plate are investigated in this paper. The analysis utilises the characteristic currents for the slots determined under the quasistatic approximation. The equivalent magnetic currents on the slots and the radiation pattern are determined when the array of slots is illuminated by a transverse electromagnetic wave incident in the waveguide, or by a transverse electric plane wave incident in the upper half-space. Analytic expressions, in the case of a single slot, are also given.