Rotman lens design issues

Traditional Rotman lenses can be designed using mathematical formulations (Rotman, W. and Turner, R.F., 1963; Gagnon, D.R., 1989; Hansen, R.C., 1991). The design equations, however, do not specify the shape of the sidewall that joins the lens focal ports to the lens array ports, and while they specify the port locations they do not specify the port widths. These parameters can substantially affect lens performance, especially side lobe level and coupling between nearest-neighbor ports. Other problems, not addressed by the Rotman equations, include phase front curvature along the array ports and energy leakage in microstrip and stripline lenses. In order to evaluate various lens designs, numerical models have been developed to predict the N-port scattering matrix of lenses. In the course of a series of design projects, these models have been implemented for four different lens realizations: microstrip, stripline, and waveguide using both horizontally and vertically oriented rectangular waveguide feeds (Peterson, A.F. and Rausch, E.O., 1992; 1999; Rausch and Peterson, 1992; 1997). The paper presents the lens performance of various designs evaluated with the models or by experimentation.