Showing papers by "Yahya Rahmat-Samii published in 2020"

A Novel Collapsible Flat-Layered Metamaterial Gradient-Refractive-Index Lens Antenna

Abstract: With the advent of small-scale satellite technologies, there has been significant interest in developing low-profile antennas. This article presents a novel collapsible flat-layered lens based on gradient-refractive-index (GRIN) metamaterials. The 3-D lens consists of multilayer double-sided microstrip square-rings units of variable sizes distributed on planar dielectric substrates to satisfy the required refractive index distribution. Adjacent layers can be stored compressed in a stacked configuration with minimal height, then deployed to an operational arrangement to their full dimensions and capabilities. The key factor in this design is the judicious choice of the discretized metamaterial unit cell such that neighboring layers are separated by an air gap, which allows the lens to collapse. A proof-of-concept prototype operating at 13.4 GHz with a 11.2 cm diameter and a height of 0.4 and 2.1 cm in collapsed and operational arrangement, respectively, was manufactured within fabrication tolerances. A resonant patch array feed was used and the lens antenna was measured in the UCLA Plane Bi-Polar Near-Field measurement range achieving a 23 dBi directivity and 22.2 dBi gain. The numerical and experimental results agree well and demonstrate that this new lens is advantageous in terms of low packaging height without compromising high-performance.

3-D Printed Microfluidics Channelizing Liquid Metal for Multipolarization Reconfigurable Extended E-Shaped Patch Antenna

Abstract: In this article, we present a novel multipolarization reconfigurable extended E-shaped patch antenna with liquid metal (LM) tunable slots. The polarization reconfiguration is achieved by tuning and switching the slots with continuous movement of LM plugs in the 3-D printed microfluidic channels. The proposed antenna topology is reconfigurable among multipolorizations including dual circular polarizations (RHCP and LHCP) and linear polarizations with arbitrary orientation within the $xy$ plane with a single feed. A thorough and comprehensive circuit model analysis for asymmetric E-shaped patch is presented. A prototype has been designed, fabricated, and assembled with an improved in-house developed process flow. The measurement results on constructed prototypes show good agreement to the full-wave simulation.

Enabling the Internet of Things With CubeSats: A Review of Representative Beamsteerable Antenna Concepts

Abstract: The advent of CubeSats has empowered the vision of using a satellite constellation to provide seamless Internet coverage across the globe. This vision, known as the Internet of Space (IoS), is the key enabler of the Internet of Things (IoT). One of the major challenges in making IoS a reality is the development of an antenna system that can sustain a high data-rate link while being amenable to integration with the small CubeSat form factor. This challenge is further magnified by the requirement that the antenna dynamically reconfigures its radiation pattern to illuminate geographical areas that demand more coverage. The aim of this article is to provide an overview of antenna concepts developed by representative researchers that can overcome these challenges. If properly tailored for specific CubeSat applications, these concepts can make CubeSat-based IoS a realizable vision. We also highlight the open challenges and technology gaps that future research must address to make IoT a reality.

A Crossed Dipole Phased Array Antenna Architecture With Enhanced Polarization and Isolation Characteristics

Abstract: A dual-polarized planar phased array antenna with enhanced polarization and isolation characteristics for multifunction applications is presented. A bent crossed dipole is selected as the element of the array antenna. The bend angle is optimized to widen the E-plane active element pattern of the dipole resulting in a pair of matched co-polar patterns. Contrary to common patch array antennas, this design does not require a continuous grounded substrate. This diminishes the surface wave propagation along the ground plane. Efficient techniques, applied to the element design, isolate the two polarizations from each other. Higher than 40 dB port isolation is achieved within the entire frequency range of 2.7–3.0 GHz in principal plane scanning. In order to preserve the symmetry of the array antenna, a mirrored arrangement in both orthogonal directions is applied to the array configuration. This enhances the co- to cross-polarization levels to better than 45 dB in scanning up to ±45° in the principal planes. The proposed phased array antenna with enhanced polarization purity can potentially improve polarimetric performance.

3D-Printed Inhomogeneous Dielectric Lens Antenna Diagnostics: A Tool for Assessing Lenses Misprinted Due to Fabrication Tolerances

Abstract: It is difficult to manufacture 3D-printed voxelized inhomogeneous lens antennas exactly to specifications due to fabrication tolerances. Here, we define fabrication tolerances as the sum total of voxelization errors plus printing errors. In this article, we show that the aperture phase is a sensitive function of these fabrication tolerances. A conservative estimate of p0.127-mm error in the amount of material specified to be printed leads to a 1.63d phase error per cell. This error accumulates, as a voxelized lens is generally made of many cells. We present a novel method for diagnosing misprinted lenses and reverse engineering the true permittivity inhomogeneity profile of a lens fabricated within specified tolerances. The technique is based on an inverse-scattering tool that uses geometrical optics (GO) and particleswarm optimization (PSO). Once the actual permittivity profile is found with our method, a new optimal focal point can be calculated by using the same GO-PSO optimization tool to determine where to best feed the misprinted lens. Both numerical and measured examples are given to validate the process. The measured results show that at the new optimal focal point, the measured directivity has been restored to that of the original design specifications.

Development of Novel K-band Beam Steerable Reflectarray for CubeSat Internet of Space

Abstract: The vision of providing global network coverage with a CubeSat constellation to enable Internet of things has escalated the demand for beam steerable antennas that are compatible with the tight form factor and limited power budget on CubeSats. In this work, we conceptualize a circularly polarized beam steerable reflectarray for CubeSat applications in K-band. The reflectarray unit cell consists of four Archimedean spiral arms and can be switched by PIN diodes to provide four discrete phase states. Beam scan in the desired elevation and azimuth angle can be obtained by appropriately addressing the diodes in each unit cell. Reflectarray prototypes were measured and RHCP beam scan up to 60° in elevation over the frequency band of 17.8 - 20.2 GHz has been achieved.

Flat Meta-Lens Antenna Synthesis Via Geometrical Optics and Particle Swarm Optimization

Abstract: A customized numerical synthesis algorithm for the design of flat meta-lens antennas is presented. The algorithm is based on a linkage between Geometrical Optics (GO) and Particle Swarm Optimization (PSO). The presented technique, which was previously applied for the design of shaped inhomogeneous lens antennas, is now applied to synthesize flat meta-lens antennas. It is general enough to synthesize the inhomogeneity of a flat meta-lens for any desired aperture phase with circular symmetry. An example of an on-axis fed flat meta-lens optimized for uniform aperture phase is presented. Another flat meta-lens is synthesized based on the assumption of previous works that the ray path is straight within the volume of the lens. Full-wave simulation results for the two lenses demonstrate the superior performance of the optimized flat meta-lens and validate the algorithm.

Beam Steerable Reflectarray Enabling CubeSat Internet of Space: Conceptualization and Design (Invited Paper)

Abstract: The vision of Internet of Things (IoT) has evolved the needs of providing seamless connectivity between devices across the globe. A potential solution to this requirement is to launch a CubeSat constellation that can provide broadband Internet access to rural and undeveloped areas (Internet of Space (IoS)). This has escalated the need for low-cost, low-profile antennas with wide angle beam steering capabilities. In this work, we elaborate on the design of a broadband, circularly polarized reflectarray capable of dynamic beam steering in the frequency range of 17.8-20.2 GHz. The reflectarray unit cell consists of a set of four copies of rotated Archimedean spiral arms, and the desired phase shift is obtained by suitably switching between these arms through PIN diodes. Representative prototypes have been fabricated and measured, and beam scans up to 60° have been achieved.

Multi-Layered Flat Metamaterial Lenses: Design, Prototyping and Measurements

Abstract: Multi-Layered flat metamaterial lenses have been proposed as lightweight and thin alternatives to conventional homogeneous dielectric lenses. In this work, we first present a methodology for the refractive index synthesis of flat meta-lens antennas based on a linkage between Geometrical Optics (GO) and Particle Swarm Optimization (PSO). The applied numerical synthesis algorithm, which was previously used to synthesize the inhomogeneity of on-axis fed lenses, is now used to synthesize both on-axis and off-axis fed flat lenses with circular symmetry thus providing conically scanned beams for the off-axis designs. Then, metamaterial elements of variable sizes distributed on planar dielectric substrates are used to form a multi-layered flat metamaterial lens and satisfy the required refractive index distribution. Simulation and near-field/far-field measured results of a proof-of-concept prototype of a multilayered flat lens operating at 13.4 GHz are also presented. Additionally, microwave holographic approach is used to evaluate the goodness of the exit aperture phase.

Design and Measurement of Low-Profile, Metal-only, Offset Parabolic Stepped Reflector Antenna for Emerging CubeSats

Abstract: The needs for low-profile high gain antennas have significantly evolved in the recent past due to the possibilities of advanced space missions with CubeSats. In this paper, we describe the development of a low-profile, offset, metal-only stepped parabolic reflector antenna which can be integrated with the CubeSat form factor with minimal deployment complexity. The reflector surface consists of multiple parabolic sections that are confocal and thus provide a collimated beam in the far-field. As a representative example, an offset stepped reflector with a diameter of 20 cm and a profile height of 7.9 mm at 19 GHz is designed, fabricated and measured. The performance of this stepped reflector is comparable to that of an ideal parabolic reflector, however with a significant reduction in profile height.

Liquid Metal-based Tunable Coaxial Antenna for Microwave Ablation

Abstract: In this paper, we propose a liquid metal tunable antenna for microwave ablation that aims to maintain the optimal impedance matching among different organs of treatment. Tuning was achieved by a pneumatic-driven physical displacement of liquid metal plug inside a dielectric tube interconnecting with the coaxial cable. Simulations were performed at the operating frequency of 2.45 GHz for the tunable coaxial monopole antenna inserted into models of liver, bone, inflated and deflated lung tissue. We demonstrated that with minor tuning of monopole length, the optimal impedance matching can be achieved among a wide range of dielectric property variations.

Link Budget Analysis of a Vehicle-to-Infrastructure System With a Switchable Circular Monopole Array

Abstract: In this paper, we examine a fixed-beam linear array for a roadside unit base station and a switched-beam circular array for a vehicular onboard unit in a vehicle-to-infrastructure communication system. The antenna gain patterns from full-wave simulations at 5.90 GHz are positioned and oriented based on a specific geometry that includes the roadside base station position and highway dimensions, and received power is estimated from Friis transmission equation. This analysis demonstrates that the range of communication for a single roadside unit base station is significantly improved by using a switched-beam circular array as an alternative to an omnidirectional antenna.

An In-Depth Understanding of Salient Features of Antenna Near-Field Measurements Through Full Wave Simulations : (Invited Paper)

Abstract: Full wave solvers today are capable of solving very complex electromagnetic problems and enable the design of complex antennas. They also allow engineers to confidently assess the antenna performance in a real-time environment prior to its fabrication and physical integration with the desired system. In this work, we use the power of full-wave simulators to understand several salient aspects of near-field antenna measurements so as to facilitate the measurement of advanced antennas for emerging technologies. The modeling of the measurement process in a full-wave solver is elaborated in detail, followed by an investigation of two representative aspects of near-field measurements, which are assessing the impact of non-ideal probe and improving the efficiency of phase retrieval algorithms.