Numerical techniques for the analysis of microstrip, stripline, and waveguide Rotman lenses

The article presents numerical formulation, based on a generalization of planar circuit analysis, that is used to test various lens designs, in order to assess the beam pattern and side lobe level in the presence of mutual coupling between feeds and the specific shape and composition of the lens sidewalls. In planar circuit analysis, the electric and magnetic fields within microstrip or stripline devices are assumed to be invariant with respect to z (their thin dimension) which permits these devices to be modeled as two-dimensional structures. A two-dimensional integral equation is used to relate the fields around the outer contour of the structure. TEM Rotman (1963) lenses were modeled this way by Chan (1989), who first introduced the use of waveguide-like modes in the feed apertures, enhancing the efficiency of analysis. The article describes the numerical formulation, including several extensions of Chan´s original analysis, and illustrates the utility of the modeling for the design of several Rotman lenses.