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The performance of both a recent rainfall rate model and the inter-annual variability prediction method proposed by the International Telecommunication Union has been assessed taking advantage of the availability of 16 years of rain gauge data. The above rainfall rate model produces as well monthly rainfall rate distributions that have been compared with the experimental monthly distributions achieving...
Physical-based rain attenuation prediction models conventionally assume a deterministic dependence of rain cell size on rainfall rate and uniaxial structure. This study examined the impact of these assumptions on attenuation predictions. In comparison with model predictions that apply an exponential distribution of cell sizes, the deterministic models exhibited a small cell size effect in which the...
For the last decades satellite communication systems have been moving towards higher and higher frequencies; rain attenuation along the Earth-satellite path can be an important limiting factor for the system availability, especially in tropical regions where rain events can be particularly intense. One of the possible countermeasures is site diversity. In this paper we evaluate the performance of...
Transmitarray antennas with dual-band and dual-polarization capabilities are studied here numerically. The antennas are designed based on linearly-polarized unit-cells working at Ka-band for satellite applications. The unit-cells include two printed patches and a connecting via; a 180° phase shift is obtained by rotating one of the patches. The dual-band property is achieved by interleaving unit-cells...
The paper presents a dual circular polarization unit cell for realizing a reflectarray that synthesizes two independent patterns based on the polarization of the incident field. To this end, a thin polarizer, which converts incident circularly polarized (CP) waves into orthogonal linearly polarized (LP) waves, is cascaded with a dual-linear-polarization (DLP) reflectarray. The reflectarray then applies...
An investigation of curved contoured beam reflectarrays with reusable surface for multiple coverages is presented. The main advantage of curved reflectarrays over shaped reflectors is that they allow the possibility of reusing a standard parabolic mold for multiple missions. To demonstrate this, two curved reflectarrays are designed using the direct optimization technique to fulfill the requirements...
Two dual reflectarray antennas able to provide an European coverage and beam scanning over 8° respectively have been presented. An accurate technique has been proposed for the analysis of dual-reflectarray antennas, which takes into account the angle of incidence of the field impinging on main reflectarray cells. Two 50-cm antenna demonstrators with the same geometry have been manufactured and measured...
The problem of efficiently and effectively compute the response (i.e., reflection coefficients) of next-generation reflectarray elements with wide number of degrees-of-freedom is addressed in this work. Towards this end, a machine learning-based approach based on advanced Kriging strategies is exploited (instead of classical full-wave solvers) in order to predict the response of complex unit cells...
A new paradigm for the design of reflectarrays is introduced. The proposed methodology allows the designer to specify constraints/simplifications on the antenna surface current distribution thanks to an innovative exploitation the non-radiating (NR) component, which is regarded a powerful additional degree-of-freedom (DoF) in the synthesis process. An illustrative example is presented, aimed at nulling...
In this paper, aberration theory will be introduced to estimate the frequency characteristics of reflectarrays. By introducing aberration theory, the mechanisms of the frequency characteristics of the beam squint and the phase errors on the aperture will be qualitatively clarified. The validity will be quantitatively verified by simulations.
Two techniques are compared for the crosspolar optimization of reflectarray antennas using a full-wave analysis technique based on local periodicity directly in the optimization process within acceptable computing time. The first one is based on the Levenberg-Marquardt Algorithm (LMA) while the second technique is based on the generalized Intersection Approach framework using the LMA as backward projector...
In this paper, we present validation of a method for constructing a virtual omnidirectional antenna in the azimuth plane. The virtual omnidirectional antenna utilizes a combination of data from directive horn antennas. The aim is to utilize the high gain of the horn antenna to improve the dynamic range of channel sounding measurements conducted in the centimeter and millimeter wave bands. The resulting...
Ray-based and hybrid propagation models are today considered as valuable solutions to fulfill 5G wireless channel modeling requirements. They are a complement or alternative to the stochastic approaches when link-level and system-level simulations deal with millimeter-wave (mmWave), ultra-dense deployment and/or large antenna arrays. The present article proposes an extension of an urban ray-based...
Professor Per-Simon Kildal passed away on April 21, 2016, after a very short period of illness. He was born on July 4, 1951. He chaired the Division of Antenna Systems of the Department of Signals and Systems at Chalmers University of Technology. He authored an antenna textbook and many journal articles and conference papers. He designed two very large antennas, including the Gregorian dual-reflector...
Professor Per-Simon Kildal passed away on April 21, 2016, at age 65. Since 1989, he was a Professor with Chalmers University of Technology, Gothenburg, Sweden, where he led the Division of Antenna Systems of the Department of Signals and Systems. The life of Professor Kildal was dedicated to Science, Education and Engineering. This paper summarizes these three aspects of his life, starting from his...
Per-Simon's rise to fame started at the Norwegian University of Science and Technology in Trondheim in the late 1970s. In this paper I will reflect on those years and how it may have shaped his career.
A comparison of Radar Cross Section (RCS) measurement results between several French measurement indoor facilities has been organized in the framework of a French Working Group (Groupe de Travail sur les incertitudes en chambre anéchoïque: GTi), dealing with measurement uncertainties in anechoic chamber. The GTi involves 22 laboratories that are either industrial or academic research ones, or laboratories...
A novel procedure is presented for the evaluation of integrals involving singular Green function and Rao-Wilton-Glisson basis functions with arbitrary mutual non-planar geometrical configuration which appear in surface integral equations representation of Maxwell equations. The proposed procedure constitutes a generalization of our previously reported result valid for planar geometries. The method...
The Poggio-Miller-Chan-Harrington-Wu-Tsai (PMCHWT) integral equation is widely used in the scattering analysis of dielectric bodies. The RWG set is normally adopted to expand the electric and magnetic currents in the Method of Moments (MoM) discretization of the PMCHWT formulation. This set preserves normal continuity across edges in the expansion of currents. However, in the analysis of composite...
The numerical evaluation of current-based volume integral equation formulations typically involves 6-D integrals with kernels that exhibit strongly singular or weakly singular behavior when observation points coincide with source points. We demonstrate that these integrals can be reduced to 4-D integrals with smoother kernels that are amenable to numerical evaluation by means of well-established numerical...
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