A New Low Loss Rotman Lens Design Using a Graded Dielectric Substrate

In this paper, a new low loss graded dielectric Rotman lens design is presented. The graded dielectric allows for the enhanced focusing of the energy between the beam ports and the array ports of the lens, thereby minimizing the energy spill-over to the Rotman lens sides. New lens design equations are presented, which account for the change in effective wavelength and ray bending within the lens. The graded dielectric within the lens was fabricated by forming a periodic lattice of voids, with a variable density, in the lens substrate. Compared to a conventional Rotman lens, the new graded dielectric Rotman lens shows a measured insertion loss improvement of up to 2.1 dB. In addition, the degradation in peak power at the extreme scan angles is improved from 1.5 to 0.7 dB.