Phased array antennas are a critical element of modern wireless communication and sensing systems, enabling rapid electronic beam steering without mechanically moving the antenna. However, there are inherent challenges and limitations associated with phased arrays antennas. Notably, a drop in the antenna gain is observed as the beam is steered away from broadside, a phenomenon known as scan loss. Dielectric lenses, and in particular gradient index (GRIN) lenses, are a promising solution to mitigate this effect, potentially allowing for drop-in improvements to existing antennas.

Recent advances in additive manufacturing enable the realization of dielectric media with a continuously varying refractive index, allowing for more freedom in the form factor compared to conventional homogeneous or multilayer lenses. This thesis investigates the design, optimization, fabrication, and experimental validation of an additively manufactured flat GRIN lens to enhance the scan coverage of a planar phased array antenna.

A workflow for the realization of GRIN media using single-material fused filament fabrication (FFF) is presented. Spatially varying effective permittivity is achieved through sub-wavelength dielectric crystals based on triply periodic minimal surface (TPMS) structures, enabling continuously varying GRIN profiles. The dielectric properties of printed polylactic acid (PLA) are characterized experimentally using a split post resonator setup (courtesy of IT’IS). With these measurements, it is shown that PLA is suitable for proof-of-concept GRIN lenses at frequencies below 30 GHz, despite moderate dielectric losses.

A novel parametrization of GRIN lenses is introduced, in which the refractive index distribution is represented as a Fourier series expansion, normalized to the achievable minimum and maximum refractive indices imposed by manufacturing constraints. This formulation is especially well suited for use with curved-ray geometrical optics, as the gradient of the refractive index can be computed analytically. Based on this parametrization, the GRIN lens design problem is formulated as a multi-objective inverse problem, targeting a model for the ray direction and phase at the lens aperture. The optimization problem is solved using particle swarm optimization, enabling efficient exploration of a large design space with relatively low computational cost.

The proposed methodology is validated through the optimization of a Luneburg-like lens. The optimizer recovers a GRIN profile close to the ideal Luneburg lens, validating the ray-tracing algorithm as well as the fitness function. This approach is then applied to the primary design case; a flat, scan-enhancing GRIN lens for use with a planar phased array antenna. The optimized lens is experimentally evaluated in the Delft University Chamber for Antenna Tests (DUCAT) using a TMYTEK BBox 5G phased array antenna, operating at 28GHz. Measurements demonstrate an increase of +-10 degrees in the scan coverage compared to a free-space reference configuration, confirming the potential of additively manufactured GRIN lenses as a practical tool for drop-in enhancements of phased array antennas.
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Fused filament fabrication (FFF) of thermotropic liquid crystal polymers (LCPs) presents an attractive route toward lightweight components with excellent in-plane mechanical properties, enabled by molecular alignment during extrusion. However, the layer-by-layer nature of FFF leads to weak interlayer adhesion, which severely compromises mechanical performance in the build direction (Z-axis). This anisotropy limits the structural reliability of printed LCP parts under demanding conditions. Inspired by through-thickness reinforcement methods used in laminated fiber-reinforced composites, this thesis investigates the potential of z-pinning to enhance interlayer strength and damage tolerance in FFF-printed LCPs.

This work focuses on adapting the z-pinning concept, previously applied in PLA systems, to the challenges of anisotropic, shear-aligning LCPs. A z-pinning methodology is developed around the commercial filament Vectra® A950, utilizing a bottom-up insertion process enabled by custom G-code routines. Vertical pins are extruded into pre-formed voids during the print, allowing control over pin shape, height, and placement. The approach leverages standard FFF hardware, requiring only a narrow-tip nozzle and careful synchronization of extrusion timing to ensure consistent pin deposition.

Mechanical testing was conducted on both pinned and unpinned tensile specimens printed in the Z-direction. The results demonstrate that z-pinning significantly enhances performance when properly implemented. The best configuration, tall pins arranged in an ABA staggering pattern, achieved a 40% increase in peak load and a tenfold increase in energy absorption before reaching peak load. Fracture analysis revealed more distributed fracture patterns, with signs of crack deflection and arrest, indicating a transition from brittle delamination to
more progressive failure modes.

These findings validate the feasibility of z-pinning for improving the mechanical properties of 3D-printed LCP components. However, the benefits are highly sensitive to process execution, as poor pin deposition may negate reinforcement or introduce stress concentrators. The study underscores the importance of concurrent design and manufacturing development, showing that even in single-material systems, structural performance can be engineered through localized deposition strategies. This opens a path toward more robust, anisotropy-mitigated 3D-printed parts using high-performance polymers. ... Read more