The convex lens, created in XF, has a rounded face defined by the equation x(z) = sqrt( 3(z-2/3 F)2 - 1/3 F2 ). Being designed for 77 GHz with a focal distance of 25 mm, it has a radius of 30 mm and height of 10.9 mm. A second, plano-convex lens was created by placing a 2 mm disk on top of the original lens. Figure 1 is a side view of the the two lens models.
A plane wave excitation was applied from the upper Z direction and a cross section of steady state electric fields was requested. Figure 2 compares the electric fields for each model and shows the slightly improved focusing ability of the plano-convex lens over the basic lens structure.
A historical note and acceleration comparison: This example is similar in size and scope to an old XFdtd Release 5 example (late 1990s). The old example was run on a dual processor 700 MHz Pentium II computer and took 3+ hours per simulation. Due to improved algorithms in XF's calculation engine and advances in processors, simulations in the new example completed in about 2 minutes!