Analysis of Rotman lenses using a hybrid least squares FEM/transfinite element method

A hybrid procedure that combines the least squares finite element method (LSFEM) and the transfinite element method is applied to the analysis of multiport Rotman lenses. The LSFEM is employed to build a functional based on the L₂-norm of the residuals of the full first-order Maxwell equations governing the electromagnetic fields in the structure. Because the full first-order Maxwell equations are solved, the method is free from spurious solutions. The transfinite element method is used to transfer the exterior conditions in the port regions to the interior region. The method is applied to a Rotman lens to determine the field distribution in the lens and the scattering parameters. Measured results for a microstrip Rotman lens with nine beam ports and eight array ports show good agreement with theoretical predictions