Design of High-gain Directive and Beam Steering Antenna Systems Using Additively Manufactured Components
Low-cost high-gain beam-steering antennas are considered the most critical component for the next generation of wireless standards that are based on using constellations of Low-Earth-Orbit (LEO) satellites beaming high-speed internet across the world. Because of commercial material and manufacturing techniques, conventional beam-steering antennas are expensive and need specialized facilities. There is a growing interest in Additive Manufacturing (AM) of Radio Frequency (RF) structures because of its reduced design complexity, low cost, increased flexibility, and rapid prototyping using Commercial Off-the-Shelf (COTS) filaments. This dissertation presents the use of AM and COTS filaments to design versatile and low-cost front-end antennas including beam-steering systems. The beam-steering design is based on the near-field meta-steering strategy where a pair of spatially designed Phase Shifting (PS) structures are placed above a high-gain antenna and are rotated to move the beam in large conical regions.
Near-field Phase Rectification Component (PRC)s are designed to improve radiation performance of Resonant Cavity Antenna (RCA)s by converting non-uniform aperture phase to relatively planar phase response. Two different types of phase rectification components are developed using Polylactic Acid (PLA) and Acrylonitrile Butadiene Styrene (ABS) filament. The first prototype is highly transmitting non-planar Phase-Rectifying Transparent Superstrate (PRTS) for RCA. The Fused Deposition Modelling (FDM) technique yielded the prototype in less than 4 hours, with, an equivalent material cost of US$ 2.5, which is considerably less compared to the traditional machining methods. Numerical and experimental investigations reflect a significant increase in the antenna performance encompassing a 7.3 dBi increase in the antenna peak directivity (from 13-20.3 dBi), 10.6 dBi reduction in Side-lobe Level (SLL) and an improvement of aperture efficiency by 36.1%. The second PRC prototype was low-cost planar Additively Manufactured Perforated Superstrate (AMPS), which was realized by printing square perforations in ABS material. The prototype weighs 139.3 g, which corresponds to the material cost of US$ 2.1. The far-field radiation performance included directivity improvement from 12.67 dBi to 21.12 dBi and reducing SLL from -7.3 dBi to -17.2 dBi. Results indicate improved radiation performance of RCA with AMPS compared to PRTS because of its planar geometry and use of a low-loss filament.
Numerical simulations and design process of PRCs manifested vital effect of superstrate on the wideband performance of RCA. Rigorous analysis was performed to design Three-dimensional (3D) printable superstrate with a small footprint to realize ultra wideband Compact Resonant Cavity Antenna (CRCA). Permittivity Gradient Superstrate (PGS) with a small footprint area of 2.86λ2 L was realized by material characterization of commercial ABS filament. The superstrate was printed in one hour and 43 minutes with an equivalent material cost of US$ 0.41 using the 3D printing filling technique. A measured 3dBi directivity bandwidth of 49.65% with peak directivity of 16.05 dBi was achieved, which is comparable to traditional CRCAs with a small footprint.
Beam steering systems are designed from additively manufactured engineered materials that are not commercially available. These materials are arranged with gradient phase delay to realize passive beam steering structures. The structures are placed in the near-field region of a base antenna, which has a fixed beam and the two structures are rotated independently to steer the beam in both azimuth and elevation. Two different pairs of beam steering structures are developed using commercial ABS and PREPERM®ABS1000 filament. The first prototype provides detailed designs and quantitative comparison of two systems with a conical horn and RCA as base antennas. Filling percentage is varied in unit-cells to engineer materials with effective permittivity lower than the host material and then unit-cells are joined in progressive phase delay to realize Perforated Dielectric Structure (PDS). A pair of PDSs transforms the aperture phase and tilts antenna response to an offset angle in azimuth and elevation with a 70◦ vertex angle. The measured results show that the RCA-based system has a peak gain of 17.7 dBi compared to the 16.6 dBi gain obtained with the horn-based system. The former possesses a larger 3dBi measured gain bandwidth of 1.2 GHz compared with the 0.7 GHz bandwidth of the latter, but at the cost of a 35.6% increase in the total height of the antenna system. The second prototype comprises synthesized meta-atoms with effective permittivity lower and higher than the permittivity of PREPERM®ABS1000. Continuous permittivity range between 2.6 and 21.4 is achieved using a single filament, which has a base permittivity of 10. The synthesized meta-atoms are arranged with gradient phase delay to form 3D printable Metal Dielectric Composite Metasurface (MDCMS) for beam steering. A pair of MDCMS is used as Risley prisms to rotate radiation response of circular patch array in conical volume with an apex angle of 114◦ by mutual physical rotation of two surfaces. A peak directivity of 19.9 dBi was achieved with less than 3dBi directivity variation.
