Design and analysis of bifurcated twin dielectric slab loaded rectangular waveguide. Dual frequency array elements

The design and analysis of a unique dual frequency array element and three probe element exciters for aperture sharing at two widely separated frequency bands is presented. The bifurcated twin dielectric slab loaded rectangular waveguide element simultaneously supports a single low frequency band phase center and four independently controllable high frequency phase centers, resulting in the formation of an independent radiating beam in each band. The principle element design objective is to minimize the element count while maximizing the rejection of high frequency grating lobes. It is shown that the slab loaded element results in 21 percent fewer phase and frequency control per unit array area than an alternate diplexed wide band element dual frequency concept for a scanning array operated over 15 percent bands centered at 4 and 8 GHz. The radiation and coupling properties of the array element are developed from a scattering formulation of the feedguide - free space discontinuity for the fully excited infinite array. Comparison of theoretical performance for triangular and rectangular grid configurations shows that considerable improvement in high frequency grating lobe rejection is obtained from the triangular lattice. To characterize the transverse aperture fields, a complete modal description of propagation in the inhomogeneously loaded guide is obtained through a component-by-component comparison of the degenerate eigen-functions of the structure.