Scielo RSS <![CDATA[Journal of Microwaves, Optoelectronics and Electromagnetic Applications]]> vol. 19 num. 2 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Ground-Penetrating Radar Antenna Design for Homogeneous and Low-Loss Dielectric Multilayer Media]]> Abstract Non-destructive evaluation of multilayer media represents an electromagnetic inverse problem, usually solved with analysis techniques in the time and frequency domains. The time- domain analysis technique depends directly on the accurate detection of reflected peaks measured by ground-penetrating radar (GPR), which limits this technique when the reflected pulses overlap with each other or the transmitted signal. Therefore, this paper presents a new practical methodology to obtain the antenna design requirements (operating frequency and temporal response) that avoid overlapping reflected pulses. The major finding is that the proposed methodology enables the production of specific antennas for the analyzed homogeneous and low-loss dielectric multilayer problem, serving as a practical guide for GPR antenna design. A typical pavement example is analyzed to apply the methodology, and, as a result, an ultra-wideband (UWB) directive antenna with tolerable dispersion is obtained according to the design specifications. Finally, the antenna simulations were compared and validated with measurements. <![CDATA[Project and Analysis of Quasi-Periodic PBG for Microstrip Antenna]]> Abstract In this work the influence of quasi-periodic distributions of air holes with 6, 12 and 6-fold modified symmetries, applied to the substrate of a rectangular microstrip patch antenna are analyzed. To validate the study, parameters such as S11 parameter, bandwidth, total gain, radiation pattern and electric field were investigated through computational simulations. The results obtained for all the PBG structures were compared to each other and to a reference antenna without PBG. In addition, we analyzed the resonating modes of each structure and it was observed improvements in bandwidth and gain for all modified structures when compared with the reference antenna, as well as reduction of the dielectric constant that is also recalculated. Some prototypes were built to compare the computational results to the measured results. It was verified that the measured and simulated results of return loss are in agreement and the antenna with 6-fold modified symmetry presented better performance than the others analyzed PBG structures. <![CDATA[Dielectric and Magnetic Properties of Epoxy with Dispersed Iron Phosphate Glass Particles by Microwave Measurement]]> Abstract This paper investigates the dielectric properties and magnetic properties of epoxy composites with different amount of powdered iron phosphate glass (IPG) at 8.2 GHz to 12.4 GHz using microwave technique. IPG composed of 60P2O5-40Fe2O3 (mol%) was produced by conventional melt and quenching method and crushed into powder. The IPG powder was characterized using energy dispersive X-ray spectroscopy (EDS), particle size analyzer and powder X-ray diffraction (XRD). Different amount of IPG (10-70 wt%) were dispersed in the epoxy. The epoxy-IPG composites were characterized by their morphology, elemental composition and scattering parameters using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and vector network analyzer (VNA), respectively. Reflection coefficient, |S11| increases whereas transmission coefficient, |S21| decreases with increasing IPG content in epoxy. Dielectric constant, εr' of epoxy-IPG composites were found increased with the IPG content from 3.33 to 4.69. <![CDATA[GO Synthesis of Offset Dual Reflector Antennas Using Local Axis-Displaced Confocal Quadrics]]> Abstract This work investigates an alternative numerical scheme for the solution of an exact formulation based on Geometrical Optics (GO) principles to synthesize offset dual reflector antennas. The technique is suited to solve a second-order nonlinear partial differential equation of the Monge-Ampère type as a boundary value problem. An iterative algorithm based on Newton's method was developed, using axis-displaced confocal quadrics to locally represent the subreflector surface, thus enabling an analytical description of the partial derivatives within the formulation. Such approach reduces discretization errors, as exact expressions for the mapping function and its derivatives are analytically determined. To check the robustness of the methodology, an offset dual-reflector Gregorian antenna was shaped to provide a Gaussian aperture field distribution with uniform phase within a superelliptical contour. The shaped surfaces were further interpolated by quintic pseudo-splines and analyzed by Physical Optics (PO) with equivalent edge currents to validate the synthesis procedure at 11,725 GHz. <![CDATA[Spatial Diversity Effect on the Experimental Gain of Capacity of the Outdoor Mobile Radio Channel in the 700 MHz Band]]> Abstract From measurements performed in the 700 MHz band, this paper analyzes the effect of spatial diversity on the channel capacity through the propagation of an OFDM mobile radio signal and compares with the results of a single branch providing what improvement of the capacity is attained with the SIMO system. <![CDATA[A Novel Dielectric Slab Antenna Based on Microstrip-Franklin Excitation for mm-Waves]]> Abstract This work reports the development of a novel dielectric slab antenna based on microstrip-Franklin radiators, which enables efficient impedance matching among microstrip lines, substrate and air. The proposed antenna has been designed and numerically evaluated using ANSYS HFSS®. Its directivity ranges from 6.67 to 16.24 dB, as its length is increased from 19.9 to 170 mm. The 80 mm-length antenna prototype provides 11.14% fractional bandwidth (27.96 - 31.26 GHz) and 10.5 dBi gain at 30 GHz. The proposed antenna has been manufactured and applied to an indoor digital wireless communication link to provide 6 Gb/s throughput using 64-QAM modulation format, aiming 5G applications. <![CDATA[Higher Order Mode Attenuation in Microstrip Patch Antenna with DGS H Filter Specification from 5 to 10 GHz Range]]> Abstract This work proposes the application of a slot in the ground plane, Defected Ground Structure (DGS), of a microstrip patch antenna. The application of this technique aims to attenuate higher-order excited modes without deteriorating the antenna parameters in the fundamental mode. The methodology for the design of the slot in H-format is presented, based on the physical dimensions of the microstrip patch antenna. The positioning of the DGS concerning the feed line was determined from a detailed parametric analysis. The antenna was designed for the fundamental mode at 2.45 GHz frequency. Two antenna prototypes were built, with and without DGS, and measurements of reflection coefficient, gain, and radiation pattern were performed. The measured results show that the application of DGS considerably attenuated higher-order excited modes. A good agreement between simulated and measured results is achieved. <![CDATA[Synthesis and Mechanical Reconfiguration of Ground Plane Tilted Microstrip Antennas Based on Tetra-Circle Fractals]]> Abstract A synthesis procedure of a mechanically reconfigurable antenna based on tetra-circle fractal patch elements is presented, enabling to change both resonant frequencies and radiation pattern performance. The antenna geometry reconfiguration is implemented by tilting the ground plane of the microstrip antenna with respect to the fractal patch and substrate layer. The tilt angle is defined as the angle between the back of the dielectric substrate and the tilted ground plane and is electromechanically varied using a thin rod of dielectric material sliding up and down, in a simple geometry. Simulation results for the proposed antenna parameters are obtained using Ansoft HFSS software. In addition to promoting frequency and pattern reconfiguration, the tilting of the ground plane has proven to be an alternative to increase the antenna gain and enable single-band or dual-band operation. Prototypes were fabricated and measured for comparison purpose showing a good agreement between simulation and measurement results. <![CDATA[Transistor Avalanche Non-Coherent Pulse Generator]]> Abstract A transistor avalanche noise generator (TANG) is described. It is based on an off-the-shelf RF transistor with an integrated planar monopole. From a 70 V DC power it generates sub-nanosecond pulses with amplitudes close to 1 V. The proposed solution does not employ step recovery diodes, and it is based as the name implies on the operation of a bipolar transistor crossing into the avalanche region. Radiation measurements showed energies close to −40 dBm at frequencies near 600 MHz, with energies reaching the range of 1 GHz. <![CDATA[GPU Finite Element Method Computation Strategy Without Mesh Coloring]]> Abstract A GPU-adapted Finite Element Method (A-FEM) implementation without using a mesh coloring strategy to avoid race conditions is presented. All the elements are simultaneously processed, and the local data is computed and consolidated into the device memory in a new adapted Coordinate Format data structure (a-COO). The comparison between the proposed solution and two GPU Element-by-Element Finite Element Method (EbE-FEM) approaches shows promising results since it is no longer necessary the mesh coloring step. This new approach is well suited for problems that need re-meshing and consequently would need re-coloring, e.g., adaptive mesh refinement. <![CDATA[A Novel Tri-bandpass Filter Side-coupled Square Ring Based]]> Abstract This work presents the design of a tri-bandpass filter based on the side-coupled square ring structure. The modeling is conceived from the classic approach of coupled transmission lines. The geometry consists of a square structure of electrical length equal to twice the wavelength of the main operating frequency, and the laterally coupled lines through which the power supply occurs. Expressions for the admittance and transformation matrix were obtained based on the impedances and admittances that model the geometry. Analyzis were performed from EM simulations. A prototype was built to validate the modeling and adjusted for operation at 0.78, 1.5 and 2.30 GHz. All results are discussed and commented, and the comparisons between simulated and measured results are coherent and in agreement, thus proving the effectiveness of the applied method. <![CDATA[Large-Scale Analysis and Modeling for Indoor Propagation at 10 GHz]]> Abstract It is essential to establish dominant propagation mechanisms in indoor environments to model propagation loss for 5th generation networks. This work presents, discusses and analyzes the data of measurement campaigns carried out in the 10 GHz band. These data were obtained in two different scenarios: a corridor and a laboratory. The measurement campaigns were conducted with horn-type directional antennas considering vertical, horizontal and cross-polarization modeling under line-of-sight conditions, where horizontal polarization antenna modeling is the differential of this work. The analysis and comparison of Close-In Reference and Floating Intercept models on a large scale are supported by analysis and considering propagation mechanisms such as reflection and diffraction, which includes calculations of optimal propagation exponent values for each of the polarization in each scenario