Reconfigurable Antennas: Design and Applications Costantine, Joseph; Tawk, Youssef; Barbin, Silvio E. ...
Proceedings of the IEEE,
2015-March, 2015-3-00, 20150301, Letnik:
103, Številka:
3
Journal Article
Recenzirano
The advancement in wireless communications requires the integration of multiple radios into a single platform to maximize connectivity. In this paper, the design process of reconfigurable antennas is ...discussed. Reconfigurable antennas are proposed to cover different wireless services that operate over a wide frequency range. They show significant promise in addressing new system requirements. They exhibit the ability to modify their geometries and behavior to adapt to changes in surrounding conditions. Reconfigurable antennas can deliver the same throughput as a multiantenna system. They use dynamically variable and adaptable single-antenna geometry without increasing the real estate required to accommodate multiple antennas. The optimization of reconfigurable antenna design and operation by removing unnecessary redundant switches to alleviate biasing issues and improve the system's performance is discussed. Controlling the antenna reconfiguration by software, using Field Programmable Gate Arrays (FPGAs) or microcontrollers is introduced herein. The use of Neural Networks and its integration with graph models on programmable platforms and its effect on the operation of reconfigurable antennas is presented. Finally, the applications of reconfigurable antennas for cognitive radio, Multiple Input Multiple Output (MIMO) channels, and space applications are highlighted.
The usage of unmanned aerial vehicles (UAVs) as flying base stations (FBSs) for expanding coverage and assisting the terrestrial cellular networks constitutes a promising technology for 5G and ...beyond. A crucial parameter affecting cellular network design is path loss prediction. An alternative to the accurate, though time-consuming, propagation prediction with deterministic Ray Tracing models could be Machine Learning (ML) based predictions. Ensemble Learning techniques are used in order to optimally combine the predictions of standalone models. That is, they combine the best-performing individual models into a better-performing meta-model. Our proposed method of the evolutionary tuned stacked ensemble optimizes the ensemble as a whole, instead of optimizing its individual base learners. To the best of our knowledge, this is the first time that an evolutionary technique is applied in order to mutually tune an ensemble's base learners for a path loss modeling problem in electromagnetics. Moreover, we present a model that works in more than one frequency. As opposed to the standard implementation of ensemble learning, our method offers a significant performance boost with low complexity.
In this paper, an antenna system that is composed of eight radiating elements is presented. The eight elements consist of a set of four curved dipoles and another set of four straight dipoles, ...providing two diversity antenna structures. Each curved and straight dipole is designed to produce a focused gain pattern toward one dedicated quadrant. A parasitic printed reflector is introduced into the center section of the top layer of the proposed antenna to enhance the matching and the gain pattern redirection capabilities of each radiating element. In addition, the printed reflector further enhances the isolation between the various elements. The assessment of the proposed diversity antenna system is performed in a rich multipath environment for various propagation scenarios. A diversity gain between 16.5 and 19.1 dB is attained for a 1% probability level and by assuming a Rayleigh fading channel for both structures. The control of the feeding of the various elements for both diversity structures is achieved through the design and incorporation of four reconfigurable feeding networks within the antenna system. Fabrication and testing of various prototypes display very good agreement between the simulation and measured results, which validate the presented designs.
UHF Deployable Helical Antennas for CubeSats Costantine, Joseph; Tawk, Youssef; Maqueda, Ignacio ...
IEEE transactions on antennas and propagation,
2016-Sept., 2016-9-00, 20160901, Letnik:
64, Številka:
9
Journal Article
Recenzirano
The design process and the deployment mechanism of a quadrifilar helix antenna (QHA) and a conical log spiral antenna (CLSA) are presented. The two antennas are proposed to operate in the UHF ...frequency band. They are composed of conductors that are embedded and supported by innovative structural techniques. This allows efficient folding, packaging, and deployment once in space. The conductors in the QHA are composed of beryllium copper and are supported by helical arms of S 2 glass fiber reinforced epoxy. The CLSA, on the other hand, has conductors that are made out of a mesh of phosphor bronze and incorporated inside thin insulators composed of continuous fiber composites. The new aspects of these designs lie in their structures and deployment mechanisms. The deployment mechanisms for both antennas include helical pantograph and origami patterns such as Z-folding configurations. Both antennas are fabricated and tested for both deployment and radiation performance. A comparison is executed between both designs, and their potential deployment possibilities from CubeSats are also investigated.
The voltage distribution along the non-linear resistance of metal oxide surges is of great importance for their proper operation, since the non-uniform potential distribution results in higher ...thermal stresses of the varistor discs near the high voltage electrode, leading to a faster ageing of the discs at the top and, consequently, a downgrade in arrester effectiveness and reliability or even failures. The current work deals with the examination of the voltage distribution along the non-linear resistance of medium voltage metal oxide gapless surge arresters, using an appropriate computer tool, discussing configuration that improve the voltage distribution. Moreover, the impact of various factors on the voltage distribution is examined. The extracted results can contribute to the more efficient design of modern metal oxide gapless surge arresters, in an effort to ensure their reliable operation to protect the electrical equipment against lightning surges.
This paper describes the synthesis method of linear array geometry with minimum sidelobe level and null control using the particle swarm optimization (PSO) algorithm. The PSO algorithm is a newly ...discovered, high-performance evolutionary algorithm capable of solving general N-dimensional, linear and nonlinear optimization problems. Compared to other evolutionary methods such as genetic algorithms and simulated annealing, the PSO algorithm is much easier to understand and implement and requires the least of mathematical preprocessing. The array geometry synthesis is first formulated as an optimization problem with the goal of sidelobe level (SLL) suppression and/or null placement in certain directions, and then solved by the PSO algorithm for the optimum element locations. Three design examples are presented that illustrate the use of the PSO algorithm, and the optimization goal in each example is easily achieved. The results of the PSO algorithm are validated by comparing with results obtained using the quadratic programming method (QPM).
We experimentally demonstrate for the first time the degenerate band edge (DBE) condition, namely, the degeneracy of four Bloch modes, in loaded circular metallic waveguides. The four modes forming ...the DBE represent a degeneracy of the fourth order occurring in a periodic structure where four Bloch modes, two propagating and two evanescent, coalesce. The DBE is associated with four Bloch eigenmodes representing wave propagation in the periodic structure that coalesce in both wavenumbers and eigenvectors (i.e., polarizations), at a single frequency. It leads to a very flat wavenumber-frequency dispersion relation, and the finite-length structure's quality factor scales as N 5 , where N is the number of unit cells. The proposed waveguide in which DBE is observed here is designed by periodically loading a circular waveguide with misaligned elliptical metallic rings. We validate the existence of the DBE in such structure using measurements, and we report good agreement between full-wave simulation and the measured response of the waveguide near the DBE frequency; taking into account metallic losses. We correlate our finding to theoretical and simulation results utilizing various techniques, including dispersion synthesis, and scaling of the quality factor and group delay with length. Moreover, the reported geometry is only an example of metallic waveguide with DBE: DBE and its characteristics can also be designed in many other kinds of waveguides and various applications can be contemplated as high-power microwave generation in amplifiers and oscillators based on an electron beam interaction or solid-state devices, pulse compressors, and microwave sensors.
Thermally induced chemical vapor deposition (CVD) was used to study the formation of nitrogen-doped graphene and carbon films on copper from aliphatic nitrogen-containing precursors consisting of C1- ...and C2-units and (hetero)aromatic nitrogen-containing ring systems. The structure and quality of the resulting films were correlated to the influence of the functional groups of the precursor molecules and gas phase composition. They were analyzed with SEM, TEM, EDX, XPS, and Raman spectroscopy. The presence of (N-doped) graphene was confirmed by the 2D mode of the Raman spectra. The isolated graphene films obtained from nitrogen-containing precursors reveal a high conductivity and transparency compared to standard graphene CVD samples. Precursors with amine functional groups (e.g., methylamine) can lead to a direct formation of graphene even without additional hydrogen present in the gas phase. This is not observed for, e.g., methane under comparable CVD conditions. Therefore, the intermediate gas phase species (e.g., amine radicals) can significantly enhance the graphene film growth kinetics. Kinetic and thermodynamic effects can be invoked to discuss the decay of the precursors.
In this paper, the performance of a lightning protection system (LPS) on a grid-connected photovoltaic (PV) park is studied by simulating different scenarios with the use of an appropriate software ...tool. The aim of this paper is to highlight the importance of an LPS and optimize its design for the protection of equipment and personnel in case of a direct lightning strike. In particular, developed potential due to lightning strikes is examined considering isolated and non-isolated external LPS. Moreover, the effect of the separation distance on the lightning performance of the PV installation is investigated for different soil structures and grounding systems. The extracted results are expected to support the design and implementation of a secure PV park and endorse its uninterrupted operation considering techno-economically balanced protection measures.
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