M. Keer

Bio: M. Keer is an academic researcher from École Normale Supérieure. The author has contributed to research in topics: Radiation pattern & Physical optics. The author has an hindex of 1, co-authored 2 publications receiving 5 citations.

Site shielding of earth-station antennas

Abstract: This paper concerns interference in satellite earth stations, due to microwave links sharing the same frequency band, and its solution by site shielding. The uniform theory of diffraction (UTD) has been used to analyze the near field of a parabolic-reflector antenna. An extension of the UTD, in which the influence of the surface impedance is taken into account, has been applied, to calculate the diffraction from the top of the barrier. The theoretical model has been verified in a field-measurement exercise, using a three-meter earth-station antenna, located behind an existing free-standing concrete wall, with a simulated source of interference. The undesirable effects of the barrier on the gain, noise temperature, and the radiation pattern have been studied, and criteria for the clearance of the main beam have been established. Methods of improving shielding effectiveness using absorbing materials and, also, specially shaped diffracting edges have been studied, as well. Laboratory measurements of the diffraction loss of absorbers have been made, and relative advantages are presented. Design guidelines have also been given. >

TM diffraction by a partly leaky halfplane

Abstract: The paper presents a hybrid method for the computation of scattered fields from a leaky halfplane illuminated by an electric line source. The structure consists of a large array of nonuniformly spaced, thin, perfectly conducting coplanar strips near the edge of a perfectly conducting halfplane. The analysis is carried out by a combination of the integral equation and physical optics methods. The solution for the current distribution on the strips is obtained by the use of the conjugate contrast source truncation iterative algorithm. Thus, matrix inversion is circumvented and the method is particularly well suited for large arrays of strips. An approximate procedure based on a physical optics derived resistive taper is given for the synthesis of strip spacings. Numerical results indicate that a moderate increase in diffraction loss in the halfplane shadow region is feasible by a judicious choice of strip spacing. Advantages and limitations of the method are also discussed.

Measurement and Analysis of Propagation Mechanisms at 40 GHz: Viability of Site Shielding Forced by Obstacles

Abstract: Mitigation of interference among adjacent radio systems is a topic of growing interest as the spectrum occupation increases. Site-shielding techniques appear as a method of improving millimeter-wave wireless communication system design, allowing frequency reuse and reducing cochannel interference. The viability of applying such techniques to systems operating in frequency bands around 40 GHz is the aim of this paper. Several propagation mechanisms are experimentally studied, including transmission across building obstacles, depolarization, reflection, and diffraction. The performance of some theoretical models of the different scattering mechanisms has been compared with measurement results. The measuring and processing procedures have also been improved. Values of the dielectric parameters of the materials in this frequency band have been obtained and are given in this paper. The attenuation results indicate that various materials, such as mortar, brick, and concrete walls, that present large values of attenuation in decibels per centimeter, can be used to shield base stations, reducing the frequency reuse distance in radio cellular networks. It can also be concluded that there is a significant diffracted field in the shadow region of brick corners.

Diffraction at a thick screen including corrugations on the top face

Abstract: A closed-form high-frequency solution is presented for the near-field scattering by a thick screen illuminated by a line source at a finite distance. This solution is applicable to a thick screen with perfectly conducting side walls and either perfectly conducting or artificially soft boundary conditions on the face joining the two wedges. This latter condition is obtained in practice by etching on that face quarter of a wavelength deep corrugations with a small periodicity with respect to the wavelength. It is shown that the artificially soft surface provides a strong shadowing for both polarizations; thus, it is suggested that such configurations may usefully be employed to obtain an effective shielding from undesired interferences. Several numerical calculations have been carried out and compared with those from a method of moments (MoM) solution for testing the accuracy of our formulation, as well as to demonstrate the effectiveness of the corrugations in shielding arbitrarily polarized incident field.

Enhancing the Power Capabilities of the Stepped Septum Using an Optimized Smooth Sigmoid Profile

Abstract: The typical septum polarizer that has gained popularity in the literature may be unsuitable for high-power applications, due to the sharp corners in the design. In order to address this issue, the fundamentals of the septum operation are first revisited, using a graphical visualization through full-wave analysis. A septum profiled with smooth edges is next presented, with enhanced power-handling capabilities in comparison to the stepped-septum polarizer. In this work, the sigmoid function is introduced to represent the smooth contour of the septum, and to enable diverse configurations without any discontinuities. The smooth and stepped profiles are optimized using the Particle Swarm Optimization (PSO) technique. The maximum electric-field intensity around the smooth edges is investigated using a full-wave simulator, HFSS. Our observations show that the maximum electric field is reduced by 40% in comparison to the stepped septum. In Appendix 1, the numerical approach is evaluated by comparing the exact series solution for the half-plane scattering problem with the simulated results in HFSS. In Appendix 2, a septum design with rounded edges is also studied as another possible design to reduce the maximum fields.

Shielding effect of a thick screen with corrugations

Abstract: The shielding effectiveness of a corrugated thick screen is theoretically and experimentally investigated. This screen consists of a half-plane of finite thickness in which corrugations are etched on the smaller side. This structure provides a significant attenuation in the shadow region for both polarizations of the incident field; thus, it can be effectively used for protecting apparatuses from radiating interference as well as for decoupling nearby operating antennas. The shielding properties of the screen are described by a high-frequency formulation that involves closed-form expressions. An experimental setup at X band has been arranged to test the effectiveness of a corrugated screen; the field in the shadow region is compared with that of a screen without corrugations. The experimental results compare very well with those obtained by the high-frequency expressions.

Unscented Particle Filter for SOC Estimation Algorithm Based on a Dynamic Parameter Identification

Abstract: In order to solve the problem that the model-based State of Charge (SOC) estimation method is too dependent on the model parameters in the SOC estimation of electric vehicles, an improved genetic algorithm is proposed in this paper. The method has the advantages of being able to quickly determine the search range, reducing the probability of falling into local optimum, and having high recognition accuracy. Then we can realize online dynamic identification of power battery model parameters and improve the accuracy of model parameter identification. In addition, considering the complex application environment and operating conditions of electric vehicles, an SOC estimation method based on improved genetic algorithm and unscented particle filter (improved GA-UPF) is proposed. And we compare the improved GA-UPF algorithm with the least square unscented particle filter (LS-UPF) and improved GA unscented Kalman filter (improved GA-UKF) algorithm. The comparison results show that the improved GA-UPF algorithm proposed in this paper has higher estimation accuracy and better stability. It also reflects the practicability and accuracy of the improved GA parameter identification algorithm proposed in this paper.