The convex lens, created in XFdtd, 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.
Figure 1: The two lens structures.
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.