Anne-Claude Tarot

Analysis and design of a cylindrical EBG-based directive antenna

In this paper, a cylindrical electromagnetic bandgap (CEBG) structure composed of infinite metallic wires is analyzed, designed and used as a model to develop a new reconfigurable directive antenna. This structure is circularly and radially periodic, and it is excited at its center using an omnidirectional source. The analysis is based on calculating the transmission and reflection coefficients of a single cylindrical frequency selective surface (FSS) and then, considering only the fundamental mode interaction, deducing the frequency response of the CEBG structure composed of multiple cylindrical FSSs. For this structure, new analytical formulas are derived, and their accuracy is assessed compared to those obtained by the finite-difference time-domain method. As in rectangularly periodic structure case, the frequency response of the CEBG structure exhibits pass-bands and bandgaps, and it is possible to obtain directive beams by introducing defects in the periodic structure. Using this concept, a new antenna was developed to obtain a controllable directive beam. An antenna prototype, without control, was designed, fabricated, and tested. An excellent agreement was obtained between theory and experiment for both return loss and radiation patterns.

FOCUSING CHARACTERISTICS OF A METALLIC CYLINDRICAL ELECTROMAGNETIC BAND GAP STRUCTURE WITH DEFECTS

The focusing characteristics of 2D-Cylindrical Electromagnetic Band Gap (CEBG) structures constituted of metallic wires and with defects are analyzed numerically for directive antennas application. The introduction of defects into the periodic structures consists of removing one or multiple wires. The simulations were carried out with a Finite Difference Time Domain (FDTD) code, where the excitation is a line source and the CEBG structure is considered infinite in the vertical direction. Numerical results showing the effects of the number of cylindrical layers and of the number of defects are presented and discussed. These results allow to determine the structures giving best focusing performance and to obtain the frequency band for directive radiation.

Dual-band CPW-fed G-antenna using an EBG structure

In this paper, a configuration is proposed to improve the performance of CPW antennas placed over an EBG material for dual band on body antenna applications. The aim was to improve the performance of such type of antennas by varying the position of the EBG with respect to the antenna. Simulation results show that the gain of the antenna is improved over the required frequency bands.

Analysis of radius-periodic cylindrical structures

The purpose of this communication is to present an analysis method for cylindrical structure which are periodic along their radii and are excited by a line source placed in the center. At first. we derive analytical formulas for the transmitted wave and the wave inside the structure of a single layer cylindrical structure, which allow to extract the characteristics of the cylindrical layer. Then we obtain the dispersion equation and the transmission coefficient of multiple layer periodic structures.

Bandwidth Enlargement of Planar EBG Antennas

A new structure based on a combination of two PRS (partially reflective surface) is introduced and studied analytically to improve the bandwidth of the FP and EBG antennas. The original procedure developed here leads to a design method for broadening the bandwidth of planar EBG antennas.

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

This 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.

Estimation of the Effective Medium for Planar Microstrip Antennas on a Dielectric and Magnetic Truncated Substrate

This letter proposes a simple formula to estimate the effective medium of planar microstrip antennas printed on a magneto-dielectric truncated substrate. The proposed empirical formulas shown in this letter yield a good accuracy with a maximum error of less than 7% for a permittivity between 1-10, a permeability between 1-10, and a ratio 0.01 <; h/W <; 0.25. These proposed empirical models are validated by electromagnetic simulations and measurements.

Pressure Dependence of the Frequency Permeability Spectra of Soft Ferrite Composite Materials: A Method of Measuring the Natural Ferromagnetic Resonance Frequency

Experimental studies on the complex susceptibility of soft magnetic composite materials (magnetostrictive Ni-Zn and Ni-Zn-Co spinels) in their region of ferrimagnetic resonance (FMR) show that the FMR is an increasing function of the applied pressure. It is shown that powders could advantageously replace their sintered materials counterpart to measure without any ambiguity the natural ferrimagnetic resonance (NFMR) frequencies of bulk materials. It is also shown that such soft ferrite composites can be realized in order to shift FMR to higher values, and to obtain low magnetic losses up to 900 MHz. High frequencies applications can be envisaged.

Wire Media - Ferrite Substrate for Patch Antenna Miniaturization

We discuss antenna miniaturization using new metamaterials, combining advantages of artificial dielectric and natural magnetic materials. It is known that the reduction of an antenna size using dielectric substrate causes the decrease of the antenna bandwidth. At the same time, the inclusion of magnetic materials into substrate allows to increase the bandwidth. It stimulates attempts to use artificial magnetics inserted into substrates of patch antennas. However, such a way did not bring considerable successes due to some reasons, mainly due to difficulties to achieve simultaneously a noticeable real part and small imaginary part of permeability in a sufficient frequency range. In this paper we propose to use as a substrate a magnetized ferrite filled with wire media whose role is to reduce the effective permittivity of the substrate. Our estimations, based on the transmission line theory, show that the radiation quality factor can be strongly minimized using the proposed substrate

Harmonic-less Annular Slot Antenna (ASA) using a novel PBG structure for slot-line printed devices

A novel PBG structure well-suited for slot-line printed devices and its application to control harmonic frequencies of an Annular Slot Antenna (ASA) are proposed. This novel PBG structure is the dual of the well-known Radisic PBG structure for microstrip printed devices. It consists of etching metallic discs on the opposite side of the slot-line.