Asymptotic evaluation of the radiation from small dielectric lenses fed by a single leaky-wave slot

When the dimensions of a dielectric lens are large in terms of the wavelength, a leaky wave type of feed radiates a space wave emerging from the feeding point of the slot, and thus appropriately excites the lens with a spherical wave. However, when the lens antenna is operating at low frequencies, this simplified ray picture is not accurate. In this paper, we present a method to evaluate analytically the near field on the lens surface, to be used as an input for a physical optics (PO) tool. The method allows to analyze dielectric lens antenna in these critical configurations, without added computational efforts. A conclusion of this paper is that the lens can in fact be used also when it is only a few wavelength in diameter, if one accounts for higher order physical mechanisms in the design phase.