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Abstract: A lens-reflector antenna comprises a hemispherical dielectric lens with a planar reflector. Beam scanning may be achieved by moving a primary feed around the fixed lens or by rotating the lens reflector with respect to a fixed feed. Truncation of the reflector and obstruction of the aperture by mechanical supports introduce scanning loss. These effects are analysed through a numerical technique where the spherical wave expansion method is used to populate an effective aperture matrix in the near field, which is then modified to account for shadowing effects. The results are verified by a measurement campaign using a scale model and by comparison with the commercial EM solver FEKO.
(ProQuest: ... denotes formulae omitted.)
1 Introduction
This investigation is driven by a resurgence of interest in the lens-reflector antenna as a multibeam or scanning antenna for communications applications [1, 2]. This class of antenna uses a planar reflector against the flat surface of a hemispherical dielectric lens, which may be a constant index, stepped-index or Luneburg lens. Ideally, a ground plane of sufficient area recovers the full aperture of a spherical lens whereas in practice a finite ground plane truncates the aperture and thus introduces scanning loss. The geometry is shown in Fig. 1. Also of interest is the case where a mechanical rail surrounds the lens and introduces further aperture blockage, which contributes to scanning loss. Since scanning loss is a critical factor in this class of antenna, we report techniques for both its estimation and mitigation.
Aperture blockage has received attention mostly for reflector antennas. In [3] the effect of blockage by the primary feed is considered by modifying the domain of integration of surface currents so that the masked portion of the aperture is removed; scattering by the supports is then considered by a ray tracing technique. In [4] the scattering by an infinite cylinder in front of a linear array of sub-apertures is considered by expressing the scattered field as a modal expansion: since a linear array is used to model the aperture this approach derives far-field patterns in one axis only for either horizontal or vertical cylinders. Shadowing by zone edges in a Fresnel lens is approached in [5] by computing the total shadowed area rather than...