J. G. Meana

Reconstructing Distortions on Reflector Antennas With the Iterative-Field-Matrix Method Using Near-Field Observation Data

This work extends the mathematical formulation of the iterative-field-matrix method for observed data from the near-field region of a Perfect Electric Conductor. The method is used as a diagnosis tool for reflector antennas, to determine the positions and extent of distortions from their idealized shapes. The new formulation is tested on a reflector antenna with several significant bumps, and excellent results are achieved. This work also presents an example where the Method of Moments is used to generate the synthetic data and the inversion is performed using Physical Optics. Such a configuration ensures that the forward model is unbiased with respect to the inversion model, demonstrating that the new formulation is also robust for these realistic scenarios.

Wave Scattering by Dielectric and Lossy Materials Using the Modified Equivalent Current Approximation (MECA)

An approximation is presented for the calculation of the equivalent currents based on the oblique incidence of a plane wave on the interface between free space and lossy dielectric media. The Snell reflection coefficients establish the relation between incident and reflected waves, then, the boundary conditions establish the equivalent electric/magnetic currents in the free space region using the total magnetic/electric fields. The interface is discretized into planar triangular facets, on which currents are assumed to have constant amplitude and linear phase variation in order to analytically calculate the scattered fields. Our modified equivalent current approximation (MECA) reduces to the well-studied physical optics (PO) formulation in case of PEC surfaces. Simulations to validate the formulation are performed over electrically large canonical geometries - a lossy dielectric sphere, a rough plate and a right dihedral - to compare the calculated Radar cross section (RCS). Good agreement between MECA and analytical/method of moments (MoM) results is demonstrated.

Cosecant-squared power pattern synthesis procedure for an hour-glass reflector antenna with sectorial beams

The aim of this communication is to present the synthesis procedure of an hour-glass antenna in order to obtain sector beams with cosecant-squared far-field power elevation pattern. This antenna is able to produce a number of sectorial and reconfigurable beams which satisfy the radiation pattern envelope (RPE) in the ETSI standard.

A PO-MoM comparison for electrically large dielectric geometries

This paper presents a comparison between PO and full wave RCS results for dielectric scattering geometries. The dihedral example shows good agreement when computing reflections, with the second contribution being the most important for the monostatic simulation. Secondly, the bistatic RCS of a larger geometry consisting of a rough surface with Gaussian incidence for PO and SDFMM shows great coincidence in the main lobe, while the reflection near grazing directions degrades for PO as expected. As a consequence, the modified PO successfully models problems which may be prohibitive for full-wave simulation.

A Shaped and Reconfigurable Reflector Antenna With Low Sidelobe Level for Cellular Wireless Communications

This letter presents a shape synthesis and an array optimization of the hourglass reflector antenna. A cosecant-squared pattern in the elevation plane, with the reconfigurable beamwidth in the horizontal plane, is achieved by controlling the excitation of the feed array elements and maintaining an invariable reflector surface. Thus, a sectorial pattern configuration of four beams (with 90 beamwidth) or eight beams can be selected in the azimuth plane. Both kinds of patterns (vertical and horizontal) have proven their usefulness and advantages for base stations in wireless communication systems.

Visibility algorithms for electromagnetic problems

Three visibility methods have been chosen with the objective of comparing their results in terms of computational time and RCS values. Two of them -trimming method, cone method - have been already described. The trimming method is considered to be the more accurate one due to the fact that only totally lit or non-lit facets can exist. Nonetheless, the computational cost is ten times the one associated with the cone method, whose relative error is 4.67%. Consequently, the employment of cone method implies a faster software execution but the price to pay is decrease of the accuracy. On the other hand, the recursive implementation of the binary space partitioning algorithm overloads the process and does not improve the results of the other methodologies.

Electromagnetic scattering for large problems with the Physical Optics - MultiLevel - Binary Space Partitioning (PO-ML-BSP) algorithm

The aim of this paper is to present Physical Optics - MultiLevel - Binary Space Partitioning (PO-ML-BSP) algorithm, which is suitable for calculating electromagnetic field levels in large scattering problems. This method combines a high frequency technique, Physical Optics (PO) approximation, with a space partition based on Binary Space Partitioning (BSP). In addition, Space Volumetric Partitioning (SVP) has been considered when the space is split into small geometrical domains (voxels) to create a multilevel scheme. The purpose is to reduce the computational cost of the analysis procedure. Monostatic radar cross section (RCS) of two spheres is compared for method of moments (MoM), PO-ML-BSP and PO-BSP (PO-ML-BSP without multilevel structure) results. Besides, coverage levels over a real scenario are calculated for PO-ML-BSP and PO-BSP configurations.

A memory-hierarchy-based optimization of MECA (Modified Equivalent Current Approximation) for the analysis of electrically large dielectric and lossy structures

Asymptotic high frequency computational techniques are widely used in modeling scenarios with electrically large scatterers. A well-known technique of this type, Physical Optics (PO), has been extensively tested in several contexts [1], [2]. Two recent works [3], [4] present a new PO analysis of dielectric and lossy geometries. In this method, called MECA, the interface is discretized into planar triangular facets. Then, the Snell reflection coefficients establish the relation between incident and reflected waves. This modified PO method successfully models problems which may be prohibitive for full-wave simulation. For the present work, we developed an OpenMP parallel version of MECA in order to reduce even more the execution time. In our parallel code, we implemented memory-hierarchy-based optimization techniques [5], [6]. As seen in the results of this paper, these techniques can improve the computational performance when calculating the scattered fields.

Multilevel scheme parameters optimization of the PO-ML-BSP method by using a simulated annealing algorithm

The optimization of the parameters of the multilevel scheme for a particular terrain has been carried out. Taking this example as reference, the results can be extrapolated to other similar maps, so an accurate calculus of the field levels with the PO-ML-BSP method is assured in these cases. The simulated annealing algorithm has minimized the function involving computational time and electric accuracy of PO-ML-BSO with respect to PO-BSP. In consequence a midway solution between time and accuracy has been achieved.

A physical optics multi-level binary space partitioning algorithm for large scattering problems

A physical optics multilevel binary space partitioning (PO-ML-BSP) algorithm for large scattering problems is presented. This method combines physical optics (PO) approximation with a space partition based on binary space partitioning (BSP) and space volumetric partitioning (SVP) in order to reduce the computational cost for the analysis procedure