Topology Optimization of RF GRIN Lenses

There is great interest in designing broadband GRadient INdex (GRIN) lenses due to their ability to improve the gain of an antenna over a wide frequency range. However, conventional approaches (e.g., transformation optics) are either difficult to realize due to the required material properties or yield suboptimal performance. Better performance can be achieved by implementing a true inverse-design (optimization) procedure which allows the lens permittivity to vary in a nearly-arbitrary manner. To this end, an adjoint-based topology optimization method is employed which can calculate gradients for an arbitrary number of design variables with only two full-wave simulations. This method is extremely versatile and can be used in conjunction with any arbitrary source, lens shape, and permittivity range to quickly find the best performing designs.