On the Asymptotic Evaluation of the Radiative Near-Field in Resonant Leaky Wave Antennas Using a Nonuniform Phase Center: Application to Small Lenses

In this work, an approach for the asymptotic evaluation of the radiative near field in resonant leaky wave antennas (LWAs) is presented. The employed spectral domain formulation is based on the steepest descent path (SDP) method of integration and utilizes a nonuniform phase center choice to improve the estimation of the first-order saddle point. In turn, the radiative near field is asymptotically evaluated by accounting for the interactions between the leaky wave (LW) poles and the saddle point. Good agreement is obtained with full-wave simulations both for LW feeds excited by electric (dipole) and magnetic (slot) current sources. To demonstrate the applicability of the proposed approach, the radiative near field is combined with Physical Optics (PO) to examine a small elliptical lens integrated with a double-slot LW feed. A physical interpretation is provided for the increased efficiency of small integrated elliptical lenses, based on the wave nature of the radiative near field in resonant LWAs.