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Abstract This paper presents a model that uses bio-inspired optimization algorithms to control of the mutual coupling (MC) in Multiple-Input Multiple-Output (MIMO) systems. The method promotes an increase in the channel throughput and a reduction in the distance among the array elements, searching values less than a half wavelength. A microstrip antenna design, at the frequency of 26 GHz, is used as a prototype for MIMO system testing and performance analysis. Genetic Algorithm (GA) is used to optimize, to determine the antenna physical parameters and to improve its performance. The mutual impedance concept is used to model the MC. The particle swarm optimization (PSO) algorithm is used to optimize the channel throughput and to reduce the distance between the elements. Simulation results show that it is possible to obtain a MIMO system performance improvement of 11.1% in channel throughput, the microstrip width is reduced by 14.5% and the distance among the elements can be reduced by 23.7%, considering the MC.Resumo em Inglês:
Abstract This work presents an adaptive hybrid signal precoding strategy for Cell-Free (CF) Massive multiple-input multiple-output (MIMO) systems. The proposed solution exploits the advantages of both distributed and centralized signal processing schemes to perform precoding. In our proposal, some access points (APs) are dynamically configured to be used in a centralized precoding scheme, whereas others are adjusted to employ a distributed method. Simulation results show that it is possible to achieve a good compromise between spectral efficiency (SE) and computational complexity (CC) in CF Massive MIMO systems finding a sensible balance between APs utilized in centralized and distributed precoding. To the best of our knowledge, prior-art solutions have not addressed an adaptive hybrid precoding method itself, they have only proposed a specific solution for each architecture, i.e., distributed or centralized.Resumo em Inglês:
Abstract This paper presents a study of a segmented waveguide where the layers are distributed following the Fibonacci sequence and aims to diminish the scattering losses usually caused by imperfections in the core boundaries of the waveguide. This phenomenon normally happens in structures which present a high contrast between the refractive index of the core and the refractive index of the clad. The analyses were obtained through observations of wave fields that propagates along the waveguide, how the effective refractive index (neff) varies along the z-direction and the study of its normalized power. The simulation of this photonic component was accomplished with the help of the Vectorial Beam Propagation Method (VBPM).Resumo em Inglês:
Abstract In this article an innovative method of studying and removing the resonances, inherently exhibit by some waveguide to microstrip transitions, is presented. By modeling an equivalent circuit, this new approach allows to obtain the constructive parameters of a finline to microstrip transition, only using the values of the resistance and capacitance components of the equivalent circuit. This procedure will allow small microwave design Companies to realize these transitions only implementing circuit analysis software, and not having to afford electromagnetic analysis software, which are very expensive and time-consuming. A full 3D electromagnetic analysis confirms that the simulation results are in excellent agreement with the results obtained by the new equations discussed in this work.Resumo em Inglês:
Abstract In this work, a theoretical model for the transmittance in a left-handed metamaterial of different geometries is presented. The proposed unit cells are a combination of conducting wires of rectangular cross-section with square-ring and hexagonal resonators. In this new dielectric compound, dependence of transmittance on the thickness of the resonators are analyzed for the particular case of normal incidence in the GHz range. It is found that the transmittance for the hexagonal resonator shows a significant increase compared to the square geometry resonator.Resumo em Inglês:
Abstract This paper presents a radiopropagation algorithm based on a Ray Tracing (RT) technique that combines a modified multipath model for constant refractivity gradient profiles and the Uniform Theory of Diffraction (UTD). A novel formulation is proposed by the authors for calculation and ground-reflection analysis of ray paths depending on atmospheric refractivity. The algorithm introduced herein was evaluated in a mixed scenario and in two more realistic case studies, under conditions of constant refractivity gradient and lossy terrain profiles. Pathloss results are obtained and compared with Parabolic Equation (PE) numerical solution results at 2.0 GHz, 3.5 GHz and 5.4 GHz. In such conditions, the modified radiopropagation multipath algorithm with atmospheric refractivity introduced herein showed satisfactory results.Resumo em Inglês:
Abstract This paper presents a feasibility study of a singlylayered dual-band reflectarray for space applications. The data links should operate simultaneously at K-band downlink frequency band 17.7-20.2 GHz with left-hand circular polarization (LHCP) and at Ka-band uplink frequency band 27-30 GHz with right-hand circular polarization (RHCP). The main aim is to present how a reflectarray can be designed so as to allow reconfigurability of its radiation pattern, especially in terms of beam steering to two different directions. The design is automated by means of a computational tool developed in MATLAB environment interfaced with the electromagnetic simulator CST Studio Suite by means of Visual Basic scripts. Simulation results are presented to demonstrate the efficiency of the proposed computational tool and reconfiguration strategy.Resumo em Inglês:
Abstract This paper suggests a slotted ground ‘S’-shaped low profile planar microstrip patch antenna for wideband and high gain operation. The suggested antenna has physical dimensions of 20mm×14mm×1.6mm having a fractional bandwidth of 111% having the operating impedance bandwidth 22.55GHz (9.12 GHz to 31.67 GHz). At 19 GHz, maximum gain of 3.9 dBi is attained. An equivalent circuit model corresponding to suggested antenna is designed by ADS software and assessed with the simulated and measured antenna results. Frequency Selective Surface (FSS) of single layer has been placed at optimum position at a distance of 15 mm below the antenna for further improvement of the overall gain of the suggested antenna. Combination of suggested antenna and 6×6 FSS configuration increases peak gain to 9.4 dBi maintaining the same antenna bandwidth. The FSS unit cell of dimension 6.5mm×6.5mm×1.6mm is used. Design of the antenna is done using commercially available electromagnetic simulator (CST Microwave Studio), and the simulated results are verified by suitable antenna measurement technique using standard microwave test bench. Given FSS integrated antenna has an overall physical volume of 39mm×39mm×15mm which makes it ideally suited for high-gain long-range applications.