Reflections inside an elliptical dielectric lens antenna

The reflections inside the elliptical lens of a typical millimetre wave antenna are investigated. In particular, it is seen that these reflections may significantly affect the input impedance of a radiating element which is located at the lens focus, owing to the presence there of a point caustic of doubly reflected rays. The presence of a caustic prevents the field prediction inside the lens by a direct application of geometrical optics. Consequently, the field inside the lens is calculated by means of the physical optics currents associated with singly and doubly reflected rays