Scattering matrix integral equation analysis for the design of a waveguide Rotman lens

An integral-equation-based procedure is developed for determining the scattering parameters of a multiport Rotman lens device. The device is intended for use at millimeter-wave frequencies and incorporates rectangular waveguide feeds. The integral equation model takes higher order modes in the feed apertures into account and incorporates mutual coupling between neighboring ports. A prototype lens was designed using the integral equation model and fabricated. The lens S-parameters were measured and modified with an ideal -40 dB (n=3) Taylor weighting function. The resulting beam sidelobe level is better than -30 dB.