Antennas Based on Rotationally Symmetric Lenses for High-Frequency Wireless Applications

QC 20240508

Abstract

This thesis investigates lens antennas for future wireless applications. The aim is to provide robust and cost-effective antenna solutions with wide-angle beam steering capabilities. The wide-angle beam steering is obtained using rotationally symmetric inhomogeneous lenses, such as the Luneburg lens. The derivation of the inhomogeneous refractive index using geometrical optics is outlined. Parallel plate waveguide (PPW) lens antennas and volumetric lens antennas are investigated. 

The studied PPW lens antennas are designed to be robust to manufacturing and assembly errors while enabling a high radiation efficiency and wide-angle steering of a fan-shaped beam. The refractive index distribution is mimicked using quasi-periodic structures or by shaping the PPW. Specifically, two robust and cost-effective glide-symmetric quasi-periodic structures are proposed. First, glide-symmetric substrate-integrated holes (SIHs) are proposed, since they enable a larger PPW spacing compared to previously reported fully-metallic designs. This large PPW spacing translates into a robust antenna solution, and the SIH structure can be cost-effectively manufactured. The presence of the dielectric introduces losses, but it is shown that these added losses are sufficiently low for many applications at K_a-band. Secondly, a glide-symmetric perforated dielectric slab is proposed to enable an even larger PPW spacing. The slab is produced using additive manufacturing and it is shown that by arranging the perforations glide-symmetrically, a wider range of effective refractive indices can be accurately realized. Again, it is shown that the added losses due to the dielectric are sufficiently low for practical applications at K_a-band. Fully-metallic (and therefore highly efficient) PPW lens antennas can be based on geodesic lenses. These lenses do not require the realization of any small features and can therefore be robust. A geodesic lens antenna demonstrator at V-band is presented, and techniques of reducing the sensitivity to manufacturing errors are proposed. These techniques are later used in the design of a geodesic lens antenna with reduced gain variation within the beam steering range compared to the reference works. This geodesic lens is based on the generalized Luneburg lens. Providing a low gain variation in the steering range ensures a good quality of service to all end users. 

Additive manufacturing provides attractive opportunities for the realization of volumetric inhomogeneous lens antennas capable of producing directive pencil beams that can be steered in a wide angular range. However, the effective refractive index range of quasi-periodic dielectric structures is often limited by the smallest realizable geometrical detail, and the reported volumetric inhomogeneous lenses are often truncated, which impacts their focusing properties. In this thesis, the impact of the lattice arrangements is discussed and it is demonstrated that by using highly symmetric lattice arrangements, the realizable effective refractive index range can be increased. Furthermore, a new lens, accounting for the manufacturing constraints, is also proposed. This lens operates similarly to the Luneburg lens, but it has a refractive index distribution that can be tuned to alleviate the manufacturing.

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