Slot coupling in dielectric lens antennas

Dielectric lens antennas offer interesting perspectives for millimeter and submillimeter wave applications owing to their capability to be integrated with electronic components. Although many contributions can be found on this topic in the literature, most of them do not pay the proper attention to the effects the lens produces on the feeding source. As pointed out in Neto et al. (1998), the geometrical properties of the elliptical lens are such that all the rays launched by a focal point-source come back in phase at the original focus after a double reflection at the lens interface. This means that a point caustic of doubly reflected rays occurs at the focal point where the primary source is located, thus affecting its input impedance. The introduction of a matching layer on the lens surface could reduce the reflections toward the feed. However, it's manufacturing may present practical problems of layer thickness control and of scarce availability of dielectric materials employable at millimeter waves. In view of this, the interaction between the various part of the primary source must be calculated accounting for reflection mechanisms excited inside the lens. For this reason, in this paper we present calculations of coupling admittances between two slots located under an elliptical lens, including the effects of the internal lens reflections. The choice of the primary source is motivated by the fact that the most used type of feeds are constituted by slots and coplanar waveguides.