Cylindrical periodic structures of metallic wires

4 pagesInternational audienceFirst, we calculate the total field for an outgoing or an incoming TM cylindrical incident wave illuminating a cylindrical periodic structure of metallic wires. Then, we give analytical formulas to extract the characteristics (reflection and transmission) of the cylindrical periodic structure. To finish, we extend the study to infinite radius periodic structure by given an approximation of the dispersion diagram

Dispersion Characteristics of a Cylindrical Electromagnetic Band Gap Structure

3 pages.International audienceIn this letter, a new analytical expression for the dispersion equation of radially periodic structures is derived. The periodic structure is considered as a set of parallel cylindrical frequency selective surfaces, and the dispersion equation is calculated by using a transmission line model. Using this result, the dispersion proprieties of cylindrical electromagnetic bandgap structures composed of continuous or discontinuous metallic wires are presented. It is shown that the band structures of these materials can be determined by using the proposed dispersion equation. Cylindrical periodic materials have potential applications for designing directive antennas, circular high impedance surfaces, or agile antennas

On the impedance matching of left-handed materials to free-space

International audienceUsing an original approach, this work shows that the intrinsic impedance, as it is usually defined, is negative for a left-handed medium (LHM) and a method to match left-handed media to free space is proposed. A full-wave technique is used to validate our analysis and proposed scheme. Our work is not in contradiction with previous studies on left-handed media and does not mean that the LHM is active, but we explain why one can encounter dificulty in simulating the excitation by an electromagnetic wave of an interface air/LHM if the LHM is considered homogeneous and we show that it is possible to excite the forward wave of a left-handed medium instead of the backward wave as it is usually done

Multi-Layer Crystals of Metallic Wires: Analysis of the Transmission Coefficient for Outside and Inside Excitation

26 pages.International audienceThis paper proposes a new analysis of the transmission coefficient at normal incidence for 2-D periodic crystals (also called Electromagnetic Band Gap (EBG) structures), which are finite in the direction of wave-propagation and are composed of metallic wires. The crystal is considered as a set of parallel Partially Reflecting Surfaces (PRSs), whose transmission and reflection characteristics are obtained rigorously using the Finite Difference Time Domain (FDTD) method. The transmission coefficient of the EBG structure is then obtained by using a plane-wave cascading approach considering single mode interactions between PRSs. The accuracy of the results given by the hybrid method is assessed compared to those obtained directly by the Finite Difference Time Domain (FDTD) method. The minima and maxima envelops and the resonance frequencies of the transmission coefficient are studied, with analytical expressions, for both, excitation from outside and excitation from inside. A discussion is also presented concerning the strength of the coefficient greater than one obtained when the plane-wave source is inside the EBG structure. In addition, by using a transmission line model, a normalized version for this coefficient is proposed, which considers the available power by the source

EBG-ANTENNA ANALYSIS : UNIFICATION OF FREQUENCY AND ANGULAR DEPENDENCIES

International audienceIn this paper, we present an original method to study planar EBG based antennas. From this method, which unifies the frequency and angular dependencies of the EBG structure, we obtain an analytical expression of the directivity of the structure versus frequency. To our knowledge, these results concerning EBG structures have never been presented

Frequency Beam Scanning and Gain Enhancement properties of PBG Antennas

The main purpose of this communication is to present the frequency beam scanning possibility of PBG-antennas and the relationship with high gain property. To this end, we will first remind the gain enhancement phenomenon and then generalize the results to the steered beam antennas

Caractérisation d'une surface sélective en fréquence cylindrique

National audienceA l'origine, la technologie des Surfaces Sélectives en Fréquences (SSF, en anglais Frequency Selective Surfaces, FSS) faisait partie du domaine militaire. Aujourd'hui, les FSS ont trouvé de nombreuses applications en électromagnétisme, micro-ondes, antennes, radar, et communications par satellite. En général leur analyse est faite pour des surfaces planes. Ici, nous nous intéressons aux Surfaces Sélectives en Fréquence Cylindriques SSFC, dans le but de les associer avec des antennes

Design of a directive and matched antenna with a planar EBG structure

The purpose of this presentation is to propose a method to design a directive and matched antenna with a planar electromagnetic band gap (EBG) structure. The EBG structure of our example consists of metallic wires. This study uses the FDTD method and analytical formulas

Directivité d'une structure antenne-matériau à BIP/cavité Fabry Pérot

National audienceLa directivité des antennes à base de materiaux a BIP ou de cavité Fabry-Perot est etudiée analytiquement

Antenna inside PBG and Fabry-Perot cavities

International audiencePhotonic crystals are used quite frequently to enhance the antenna gain. To understand the origin of this enhancement we have assimilated the PBG-Antenna structure to a Fabry-Perot cavity, where the source of the incident plane wave is placed inside. The PBG reflecting surfaces are composed of periodic metallic wires. The Fabry-Perot interferometer is usually studied with an excitation source placed outside the cavity. Here we had to extract new formulas for the case of the sources positioned inside the cavity. These simple formulas are found to be very helpful and very precise compared to the exact FDTD simulation. In the second part of the paper a simple model of the antenna is proposed to take into account the interactions between the cavity waves and th