Equivalent network for a slot-coupled elliptical integrated lens antenna
A method is presented for the design and the analysis of a dielectric elliptical lens antenna slot fed by a microstrip. The elliptical shape of the lens gives a focusing property provided that the eccentricity is properly related to the dielectric constant. In particular, under this condition, all the rays outgoing from the source are refracted in the boresight direction, thus providing the focusing phenomenon. On the other hand the lens interface gives rise to reflections. Indeed, the geometrical properties of the lens itself are such that all the doubly reflected rays launched by a focal source return in phase at the original focus. In view of this property, the availability of tools for the accurate prediction of the input impedance of the antenna including multiple reflections effects is particularly important owing to the limited tuning possibilities intrinsic with integrated technology. Regarding the feed arrangement, we propose the same as that typically used in patch antennas, namely a slot which is excited by a microstrip printed on a back substrate. This structure presents several advantages, primarily due to the physical separation between the radiating elements and the feeding network. Furthermore, with respect to the alternative slot feed arrangement involving coplanar waveguides (CPW) the present solution provides radiation pattern regularity and polarization purity, which are important features in quasi-optical receiver front-ends.