In this work, we use an in-house ray tracing (RT) model based on physical optics (PO) to efficiently design the profile of two geodesic lenses that can be additively manufactured in a single piece. These lenses are stacked and interconnected, forming a 2D beamforming network (BFN). The first set of stacked lenses consists of geodesic half-Maxwell fish-eye lenses, which allow beamsteering in the vertical plane over an angular range of 60 degrees. The second set of stacked lenses is composed of geodesic generalized Luneburg lenses, which could allow beamsteering in the horizontal plane over an angular range of 100 degrees. Within seconds, our RT-PO model determines the phase distribution created by the lenses, offering an effective approach for developing 2D BFNs. Utilizing the phase and amplitude obtained from the RT, a 2D efficient beam-steering antenna has been designed.

Implementing mm-wave antennas involves working with shorter wavelengths, which can challenge conventional design and manufacturing, especially in the context of array antennas. This may lead to prohibitive design sizes and manufacturing limitations for the arrays to prevent grating lobes from appearing. This study introduces a novel approach that combines dielectric lenses with antenna arrays that have a large inter-element spacing, aimed at reducing the occurrence of grating lobes that arise at specific scanning angles. Moreover, the proposed dielectric lens solution improves the antenna directivity in the main beam direction.

Advances in communication systems have driven the need for wider bandwidths, exceeding the limits of traditional frequency bands. This has motivated the shift towards higher frequency bands to support 5G and 6G networks [1]. At these frequency bands antennas are required to not only support ultra-wideband operation but also ensure efficient performance, provide high gain, and maintain consistent radiation characteristics across the entire bandwidth. Lens antennas, which are theoretically non-limited in bandwidth, have shown to be a suitable solution in the millimeter-wave band [2].

The combination of arrays with dielectric lenses is an attractive solution to improve the antenna performance for millimeter wave applications. The design and optimization of these lenses present significant challenges. This is primarily due to the computational intensity of simulating them with full-wave software packages, especially since an extra simulation is required to determine the nonlinear phase distribution of the array. A potential solution to accelerate the design process is the implementation of a ray tracing (RT) method. To address the limitations of our earlier in-house 2D RT model, we are currently upgrading it to a 3D version. In this context, we outline the steps involved in geometry creation and geometrical optics within the model. The geometrical optics include both reverse RT (for phase distribution retrieval) and direct RT (for radiation pattern calculation). Our results show a good agreement with the theory.

Integrating dielectric lenses with phased array antennas can be beneficial in numerous applications, yet the design procedure typically requires significant computational effort. In this work, we employ a streamlined in-house two-dimensional ray-tracing model to design dielectric lenses, with the goal of enhancing the gain of an array antenna at large scanning angles. The ray-tracing model also accounts for losses from material absorption and reflections. The interfaces between the dielectric layers of these lenses devised in this study are defined using splines to allow a large flexibility of their shape. First, dielectric lenses consisting of a core layer supplemented by two matching layers are investigated. The results show better performance compared to the lens constructed using the conic equation. In addition, multilayer dielectric lenses also provide more flexibility, as proved by the proposed configuration with five layers which also minimizes reflections in the optimized direction. Finally, a nonuniform multilayer lens, featuring two layers on the sides and a single layer near to broadside can improve gain at 60∘ while maintaining efficiency at smaller angles.

This thesis investigates the combination of array antennas with lenses to simplify the feeding networks of planar arrays in the millimeter-wave regime. Two different strategies are proposed: linear arrays of vertically stacked lenses based on parallel plate waveguide (PPW) and planar array antennas with dielectric lenses placed on top. 

Due to their large electrical size, these antennas require efficient tools to design and simulate them. In this thesis, the farfield radiation pattern is calculated using two ray tracing models that use physical optics. Both models follow three steps: calculation of ray trajectories, calculation of amplitude distribution using the ray tube theory and evaluation of farfield radiation pattern. Furthermore, these models can also calculate the radiation efficiency. For PPW-based lenses, the efficiency decreases due to the conductivity and surface roughness of the metallic plates, whereas, for dielectric lenses, the efficiency decreases due to the material absorption and reflections. 

Three PPW-based lens array antennas are presented in this thesis. First, the scanning in two planes is tested using a water drop lens array antenna and a feeding network based on a power divider and phase shifters. The antenna is manufactured in different pieces using milling. Then, a monolithic geodesic lens array antenna is designed and manufactured using additive manufacturing, which prevents leakage and misalignment between pieces. The profile of the geodesic lens requires some modifications to adapt to the manufacturing technique. Finally, a multiple-ridge lens antenna is proposed to further reduce the height profile of these antennas. Two different ridges are proposed (rectangular and trapezoidal), which are suitable for milling and additive manufacturing. This type of lens antennas can also be vertically stacked to form a linear array. 

The combination of phased array antennas and dielectric lenses is of interest in the terrestrial and satellite communications industry. Dielectric lenses can increase the gain of the array in different scanning angles or redirect grating lobes. This can help to reduce the complexity and power consumption of array feeding networks. The two designed multilayer dielectric lenses show that using other curves to define the dielectric layers provide more degrees of freedom. This together with a customized design of the lens for the specific goal helps to achieve results close to the physical limits of the lens.

Denna avhandling undersöker hur linser kan kombineras med gruppantenner för att förenkla plana gruppantenners matningsnät vid millimetervågsfrekvenser. Två olika strategier föreslås: linjära gruppantenner bestående av vertikalt staplade geodesiska linsantenner baserade på planvågledare (PPW) och plana gruppantenner med dielektriska linser placerade ovanpå.

På grund av antennernas betydande elektriska storlek krävs effektiva verktyg för att designa och simulera dem. Här beräknas fjärrfältets strålningsdiagram med två strålföljningmodeller som använder fysiskalisk optik. Dessa modeller följer tre steg: beräkning av strålbanor medelst geometrisk optik, beräkning av amplitudfördelning genom att kräva att energin bevara längs strålarna och slutligen utvärdering av fjärrfältets strålningsdiagram från strålbanorna och amplitudfördelningen. Vidare kan dessa modeller också beräkna antennens verkningsgrad. För de PPW-baserade linserna minskar verkningsgraden på grund av metallers begränsade ledningsförmåga och ytojämnheter i de metalliska plattorna, medan verkningsgraden för dielektriska linser minskar på grund av materialets absorption och reflektioner.

Tre PPW-baserade linsgruppantenner presenteras i denna avhandling. Först presenteras strålstyrning  i två plan i en gruppantenn av vertikalt staplade PPW-linser och ett matningsnät baserat på effektfördelare och fasvridare. Antennen tillverkas i olika delar med fräsning. Därefter designas och tillverkas en monolitisk gruppantenn med hjälp av additiv tillverkning, vilket förhindrar läckage och fellinjerning mellan olika delar. Profilen för den geodesiska linsen kräver vissa modifieringar för att anpassas till tillverkningstekniken. Slutligen föreslås en åsad linsantenn för att minska höjden av PPW-linsanten. Två olika åsar föreslås (rektangulära och trapetsformade), som är lämpliga för fräsning respektive additiv tillverkning. Denna typ av linsantenner kan staplas vertikalt för att bilda en linjär gruppanten.

Kombinationen av fasstyrda gruppantenner och dielektriska linser är av intresse för mobil- och satellitkommunikation. Dielektriska linser kan öka gruppantenners förstärkning vid olika styrvinklar eller styra gallerlober. Detta kan bidra till att minska komplexiteten och strömförbrukningen hos matningsnäten för dessa gruppantenner. De två designade dielektriska linserna visar att användandet av olika profiler för de dielektriska lagren i linsen ger fler frihetsgrader. Detta, tillsammans med en anpassad design av linsen för specifika mål, bidrar till att de uppnådda resultaten ligger nära linsens fysikaliska gränser.

The Luneburg lens is a graded index lens that transforms a spherical wave into a planar wave [1]. This lens can be used in a multibeam antenna with the attractive property that scanning can easily be done by moving the feed, and because of the rotational symmetry of the lens, scan losses can be small. The Luneburg lens antenna is usually implemented by discretizing its refractive index into several dielectric layers [2], using metasurfaces [3], or geodesic lenses [4]. A geodesic lens mimics the behavior of a planar graded index lens by appropriately shaping a parallel-plate waveguide (PPW) structure [5]. The resulting non-flat PPW avoids the use of dielectric materials, which are known to cause relevant material losses at high frequencies. As a result, the antenna design based on a geodesic lens can achieve high efficiency.

Ray-tracing physical-optics (RT-PO) models have been widely used to simulate array antennas combined with dielectric radomes. In this work, we present an efficient two-dimensional (2D) streamline approach to simulating a dielectric lens antenna combined with a feeding antenna. To account for the non-punctual nature of the feed antenna, the rays are shot from equidistant points with an evenly angular distribution. Once the ray trajectories that follow from the feed antenna through the lens are calculated, the far-field radiation pattern of the structure is obtained using Kirchhoff's diffraction formula. The simulation time has been notably reduced from several minutes using 2D full-wave simulations in Comsol to a few seconds using our in-house ray-tracing Physical-Optics model. The results show that, using this approach, the design of dielectric lenses can be done more efficiently.

We propose and validate experimentally a fully metallic geodesic Luneburg lens antenna operating in the subTHz band. The antenna produces three beams pointing at 0 degrees, 40 degrees, and -40 degrees. To facilitate the integration, the geodesic lens is folded to reduce its height to approximately 38.7% of the original Rinehart-Luneburg lens. To reduce potential leakage resulting from manufacturing and assembly tolerances at subTHz frequencies, the waveguide feeding structure has a deliberate small air gap alongside electromagnetic bandgap structures. This enhancement aims to bolster the robustness of the antenna, ensuring stable performance even in the presence of misalignments. The results demonstrate the robustness of geodesic lenses in the subTHz regime; showing their suitability for applications that require multibeam antennas at these high frequencies. The successful performance of geodesic lenses in the subTHz regime confirms its potential for operation at higher frequencies above 300 GHz.