Bifurcated waveguide fed broadwall slots radiating through a baffle

A recent innovation in the development of slotted-waveguide array antennas has shown that for a rectangular waveguide radiating into a ´half-space´ through slots located in the broadwall, polarisation selectivity can be achieved by even or odd mode excitation of a suitable combination of longitudinal and transverse slots in an axially bifurcated form of the waveguide. In practice, however, the external region of the guide is seldom a true half-space, particularly in the case of linear arrays, which are often modified by a short section of parallel plate waveguide to provide some degree of polarisation purification and/or spatial filtering. An analysis of this geometry is described, in which the presence of the parallel plate region has been accommodated within a moment method model of a polarisation agile slot arrangement by employing an ´imaged´ Green function to represent the parallel plate enclosure. It is also shown that particular care in identifying suitable basis functions is required in the case of the T-shaped element of the polarisation agile slot pattern which straddles the waveguide bifurcation.