K. Mahdjoubi

Active metallic photonic band-gap materials (MPBG): experimental results on beam shaper

We focus our attention on the possibilities to control the beam radiated by antennas, which are initially omnidirectional using active metallic photonic band-gap materials (AMPBG). In fact, MPBG composed of continuous or discontinuous wires present different and interesting characteristics when they are used as an antenna reflector or a radome. Adding active components on wires allows one to switch from continuous to discontinuous structures. Wires with active elements on can then be placed inside a structure, which shapes the beam radiated by a dipole antenna. Experimental results show that it allows one to switch on/off the beam or to change its shape.

Investigation of Flexible Textile Antennas and AMC Reflectors

In this paper, two different methods for fabric characterization are presented: a single frequency method and a broadband method. Felt and denim fabrics are characterized, and patch antennas are designed using these substrates to test both methods. Prototypes of the antennas on felt and denim are manufactured using conductive textile (called electrotextile) aiming to obtain fully flexible antennas. The prototypes are characterized in anechoic chamber to be compared and obtain conclusions related to the characterization methods. A new dual-band hexagonal AMC reflector combinable with antennas is also proposed to improve their performance and reduce the backward radiation to the human body. A novel broadband CPW-fed monopole antenna is designed to be combined with the AMC. The resulted prototype is characterized and compared with the performance of the CPW-fed antenna alone.

Characterization of an OAM Flat-Plate Antenna in the Millimeter Frequency Band

Electromagnetic waves bearing orbital angular momentum in the radio frequency range is a growing subject of study. The design of systems able to produce and/or to receive such waves is then of crucial importance. The aim of this letter is to characterize, in an anechoic chamber, a new type of antenna in the millimeter frequency band. The index-varying flat plate generates an electromagnetic wave carrying orbital angular momentum. We then extract the various modes from the radiated field.

Mutual coupling between stacked square microstrip antennas fed on their diagonal

Original results on mutual coupling between two identical stacked microstrip antennas are presented. The theoretical results, calculated by using the reciprocity theorem and the spectral domain method, are in good agreement with experiments. The mutual coupling between stacked structures is compared with that between unstacked patches. >

Numerical Studies of Metallic PBG Structures

Abstract—Photonic Bandgap (PBG) materials have been investigated for their versatility in controlling the propagation of electromagnetic waves [1, 2]. In order to determine PBG structures responses, several analytical or numerical methods are used, such as: • The plane wave method applied to solve Maxwell’s equations [3]. • The transfer matrix method, based on the wire grating impedance developed by N. Marcuvitz [4]. • The Finite Element Method (FEM) exhibits, e.g., the frequency response of reflection and transmission coefficients of the PBG materials when they have infinite surfaces and are excited by plane wave. The FEM method can be also used in the case of finite structure fed by a dipole. • The Finite Difference Time Domain method (FDTD). This method solves the discretized Maxwell’s equations in the time domain and evaluates the electromagnetic field components. These EM fields are then obtained in the frequency domain thanks to a Fourier Transform.

Efficient, metamaterial-inspired loop-monopole antenna with shaped radiation pattern

A new family of metamaterial-inspired monopole antennas is reported. Split-ring resonator (SRR) is introduced into the near field region of a monopole antenna. Four configurations are proposed by changing the position of the slot of the SRR. In each case, we obtain a new behavior and a new resonance frequency, in addition to that of the monopole. The results are presented for the return loss, efficiency, surface current and radiation pattern. Four prototypes are fabricated and measured. Good agreement between numerical and experimental results is demonstrated.

Superdirective and low profile metamaterial-inspired antenna

In this paper, a superdirective and low profile metamaterial-inspired antenna is reported. The proposed structure consists of the association of Split-Ring Resonator (SRR) and a monopole. This antenna of ka = 0.65 size works in the UHF band and exhibits a high directivity of 4.41dBi in the matched bandwidth of 25 MHz (-10dB). Simulated and measured results are presented for the return loss and radiation pattern.

High directive compact antenna with non-foster elements

Performance characteristics of passive electrically small antennas are limited by fundamental physics. Using active elements into antenna structures appears like an opportunity to overshoot those limits. Non-Foster elements are classically used in matching networks for electrically small antennas in order to increase their impedance matching bandwidth. In this paper, Non-Foster elements are proposed as innovative method to achieve a broadband high directive compact antenna at 868 MHz. The analysis is computed considering a three-element compact parasitic array. The impedance loads associated to each parasitic element have been calculated using an optimization procedure based on spherical wave expansion. Finally, the concept has been validated by electromagnetic simulations.

Design of a multi-band metamaterial-inspired dipole antenna with director element

In this work, we present a multiband metamaterial-inspired antenna. The proposed structure consists of a printed dipole antenna with two Split Ring Resonators (SRRs) and one director element. The addition of the resonators and the director leads to new resonance frequencies lower than that corresponding to the dipole alone with different radiation patterns. Simulation and measured results of return loss and radiation patterns are presented and analysed.

Metallic photonic band-gap materials (MPBG) as angular selective reflector or radome: application to antenna grating lobe reduction

This paper presents numerical and experimental results on metallic photonic band-gap materials (mpbg), composed of metallic wires and used as antenna reflector or radome. Attention is focused on mpbg angular response. In fact, with specified angular characteristics, MPBG materials can be interesting in order to reduce antenna grating lobes. One possible grating lobe reduction solution is based on the use of mpbg as angular filter. The radiation characteristics obtained with this solution are then improved by using a mpbg reflector to enhance the gain. Regarded to a classical metallic reflector, 20 dB and 12 dB gain improvement in the theoretical and in the experimental cases are respectively obtained, when the reflector is composed of more than two layers. The scanning performances are also presented. We show that angular filtering characteristics can be improved either by changing the array interface or by changing the mpbg lattice. In order to select the structure with the best angular behavior, an experimental and numerical characterization method is also presented.RésuméCet article présente les résultats numériques et expérimentaux sur les matériaux à bande interdite photonique métallique (bipm), composés de fils et utilisés en tant que réflecteur ou radôme. L’attention est particulièrement portée sur la réponse angulaire des bipm. En effet, certains comportements angulaires peuvent se révéler très intéressant pour réduire les lobes de réseau des antennes. Une méthode consiste notamment à utiliser un bip comme filtre angulaire. Les caractéristiques de rayonnement ainsi obtenues peuvent encore être améliorées grâce à l’utilisation d’un réflecteur bip. Ceci permet notamment d’augmenter le gain par rapport au cas d’un simple réflecteur métallique. L’augmentation est respectivement de 20 dB et 12 dB théoriquement et pratiquement, quand le réflecteur est composé d’au moins deux couches. Les performances de balayage de telles structures sont aussi présentées. Les auteurs montrent qu ’un changement du type de réseau permet d’améliorer le comportement angulaire de l’antenne tout en conservant une bonne réjection des lobes de réseau.