Fernando Jose da Silva Moreira

We present a novel modular implementation of the DGTD method to effectively address electromagnetic problems involving general doubly dispersive media. This approach includes an extended perfectly matched layer to directly truncate doubly dispersive materials, allowing for the modeling of open domains. The proposed modular and concise DGTD implementation, based on the complex-conjugate pole-residue model, offers flexibility and simplifies the handling of complex doubly dispersive medium problems with curvilinear boundaries. We apply the formulation to two-dimensional scattering problems, demonstrating very good agreement with their respective analytical solutions.

We present a novel modular implementation of the discontinuous Galerkin time-domain (DGTD) method to effectively address electromagnetic problems involving general dielectric dispersive media modeled through vector fitting. This approach includes an extended dispersive perfectly matched layer to directly truncate dispersive materials, allowing for the modeling of open domains. The proposed modular and concise DGTD implementation, based on the complex conjugated pole residue model, offers flexibility and simplifies the handling of complex medium problems. We apply the formulation to both two-dimensional and three-dimensional canonical scattering problems, demonstrating good agreement with their respective analytical solutions.

This paper discusses a polarimetric measurement campaign conducted in two distinct environments, with data collected at the Federal University of Minas Gerais (UFMG) in Brazil. The study investigates millimeter wave propagation through vegetation at a frequency of 36.6 GHz in two scenarios: the Central Square of UFMG and a forested area within the campus. In the first scenario, measurements were conducted along a main street with varying degrees of vegetation obstruction, focusing on analysing fast fading. For the fast-fading analysis, Rayleigh, Rice, and m-Nakagami distributions were considered. Results from the first scenario indicate that the m-Nakagami distribution provides the best fit for both vertical and horizontal polarisations, surpassing traditional models such as Rayleigh and Rice. In the second scenario, measurements were taken within a forested area, and the study was undertaken to analyse fast fading and excess loss. Considering the excess loss study, measurements were compared with three traditional models (CCIR, Weissberger, and COST 235). Excess loss analysis showed that traditional excess loss propagation models tend to exhibit a minimum RMS error of 10.6 dB for vertical polarisation and 15 dB for horizontal polarisation (Weissberger model), whereas the proposed model demonstrated improved accuracy over log-distance models, particularly for vertical polarisation, presenting an RMS error of 5.8 dB, and for the horizontal polarisation a RMS error of 10.2 dB, at least 4.8 dB smaller than the Weissberger model. Considering the fast fading analysis, the m-Nakagami distribution tends to provide better results in both polarisation. These findings underscore the importance of accurate propagation models tailored to specific environmental conditions, such as vegetation, to enhance the reliability of future 5G evolution and 6G microwave communication systems.

This work presents a simple formulation to synthesize amplitude and phase distributions at cylindrical apertures of omnidirectional dual-reflector antennas. Adopting a tapered amplitude, the phase is obtained to provide an omnidirectional cosecant-squared radiation pattern with low sidelobe levels. Initially, the synthesis formulation is validated by the aperture method. Then, two distinct omnidirectional dual-reflector configurations are shaped and their radiation patterns are simulated by full-wave method-of-moments analyses and by ANSYS HFSS, to illustrate the usefulness of the synthesis technique.

In the present work an analytical formulation to synthesize non-uniform phase distributions at cylindrical apertures is described. Assuming three distinct amplitude distributions, the respective phases are established to provide cosecant-squared radiation patterns. Non-uniform amplitude distributions are investigated and adopted to reduce sidelobe levels and unwanted ripples in the synthesized radiation patterns. Analytical results for the established amplitude and phase distributions at cylindrical apertures are presented. The radiation patterns for such distributions are obtained by aperture method analysis, successfully demonstrating the usefulness of the new analytical formulation.

This study proposes an analytical formulation in complex coordinates to synthesise three‐dimensional single‐shell dielectric lens surfaces. An exact formulation based on geometrical optics is developed, and the synthesis problem is modelled as a non‐linear second‐order partial differential equation of the Monge–Ampère (MA) type. An alternative numerical scheme based on axis‐displaced confocal quadrics is used to locally represent the surface of dielectric lens. The advantage of this approach is to analytically obtain the partial derivatives present in the MA equation. To validate the proposed methodology, numerical results are obtained by an iterative algorithm that allows the simultaneous control of the transmitted beam width and the power density amplitude in the far‐field region. To illustrate the synthesis effectiveness, two examples of lens antennas are simulated and analysed.

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.

The work investigates the electromagnetic performance of omnidirectional dual-reflector antennas designed to operate with a frequency bandwidth larger than 45% (25-40 GHz). We consider two antenna configurations, distinguished from each other by two different optical ray mappings. A conventional coaxial horn is designed to ensure vertical polarization and stable primary radiation pattern for both configurations along the operating bandwidth. By employing a Geometrical Optics synthesis technique, the omnidirectional reflectors are shaped to maximize the directivity of the broadside secondary radiation patterns. For the synthesis, we employ different aperture power distributions and investigate their effect on the antenna gain and return loss when operating over the 40% frequency bandwidth. To access the antenna performance, a full-wave electromagnetic analysis based on the combination of Mode Matching and Method of Moments is employed.

In this work, new formulations for the hybrid meshless‐method of moments technique are presented. The proposed approaches are applied for solving 2D electromagnetic scattering problems. The solution is obtained by dividing the problem into 2 subproblems: one internal to the scatterer and another external to it. For the internal subproblem, the meshless method is used for solving the weak form of the 2D Helmholtz equation. For the external subproblem, the Method of Moments is used for solving different combinations of electric field integral equation and magnetic field integral equation. Both subproblems are coupled by imposing the continuity of the tangential fields over the scatterer surface. The technique is applied for solving the TMz electromagnetic scattering by an infinite dielectric cylinder. Numerical and analytical results are compared to each other showing the validity and accuracy of the proposed approaches.