Shaped double-shell dielectric lenses for wireless millimeter wave communications

The main drawbacks of homogeneous dielectric lenses are the internal reflections at the lens surface, and eventually the size (typically 10-20 /spl lambda/ diameter, 5-10 /spl lambda/ depth), despite the millimeter wavelengths. This paper shows that these drawbacks can be alleviated in a shaped double-shell dielectric lens antenna. An example of a double-material lens is discussed in terms of the radiation patterns, internal reflection losses, and frequency behaviour. Geometric optics (GO) formulation is used at the first design step, and physical optics (PO) is used to obtain the actual radiation pattern. The synthesis method has been generalised for the case where two refracting interfaces are considered. An important target for millimetre wave wireless applications is the shaped elevation pattern that ideally compensates for the free-space loss in each observation direction within a cell. This corresponds to a sec/sup 2//spl theta/ radiation pattern, and it is adopted as the target pattern in the example included. Appropriate design further allows for some control of the cell spillover.