This study examines a slitted parallel plate waveguide (PPW) from the perspective of diffraction and equivalent circuit representation for a narrow slit and radiation, including the surface wave effect, from a wide slit. The fundamental differences between the diffraction and equivalent admittance properties of the slit discontinuities in typical microstrip and waveguide structures are considered by comparing how the waveguide heights of the PPW and dielectric constants filling the inside of the PPW correspond to those of the two structures, respectively.

The diffraction problem of a Gaussian beam by finite number of periodic slots in a parallel-plate waveguide filled with a homogeneous dielectric is considered. The integro-differential equation for the unknown equivalent surface magnetic current density over the slots is derived and solved by the method of moments (piecewise sinusoidal Galerkin method). From some theoretical results for the angular diffraction pattern, the present geometry is observed to simulate well the previous rectangular groove geometry from the viewpoint of scattering behaviour. In addition, two types (resonance and non-resonance types) of Bragg blazing phenomena are discussed. Simultaneous Bragg and off-Bragg blazing is also demonstrated.