Nicolas Guérin

A metallic Fabry-Perot directive antenna

We report the design of a directive antenna using the electromagnetic resonances of a Fabry-Perot cavity. The Fabry-Perot cavity is made of a ground plane and a single metallic grid. The resonance is excited by a patch antenna placed in the cavity at the vicinity of the ground plane. The two remarkable features of Fabry-Perot cavity antennas are, first, that they are very thin and second that only one excitation point is needed. A directivity of about 600 is measured at f=14.80 GHz which is to our knowledge one of the highest directivities reported for an antenna using Fabry-Perot resonances.

Combined Method for the Computation of the Doubly Periodic Green's Function

The performances of several methods used for the computation of the free space Greens function for doubly periodic arrays are investigated. We make a careful study of these methods, based on accuracy and computing time criteria. We show that none of them is able to fulfil both criteria for a large range of parameters (position in space, wavelength, periods, ... ). Fortunately, it is possible to retain three complementary algorithms. We combine them in order to implement a numerical code that automatically chooses the appropriate algorithm depending on the parameters.

Accelerated Computation of the Free Space Green's Function Gradient of Infinite Phased Arrays of Dipoles

The performances of different methods used for the computation of the gradient of the free space Greens function for doubly periodic infinite arrays are investigated, for spacings smaller than the wavelength. An optimal transition between plane wave and cylindrical wave decompositions is proposed and an extension of the method is proposed for the large wavelength case. The joint use of different wave decompositions, combined with the Levin accelerator, allows to obtain exponential convergence for all observation points.

Compact directive antennas using metallic photonic crystals

The paper presents a theoretical, numerical and experimental study for the design of a three-dimensional directive antenna for microwave telecommunications (Ku-band: 12-18 GHz) applications. This antenna uses metallic photonic crystals which act as an ultrarefractive metamaterial. This structure is much more compact than classical solutions and uses a single feeding device. The development of a numerical 3D code computing the diffraction by metallic biperiodic gratings allows this kind of antenna to be modelled and optimized. Numerical results are confirmed by experiments in an anechoic chamber.

Optimization of metallic bi-periodic photonic crystals application to compact directive antennas

This paper presents a theoretical, numerical and experimental study for the design of a three-dimensional directive antenna for microwave telecommunications (KU-band: 12-18 GHz) applications. The presented structure consists of a stack of 6 metallic crossed grids above a ground plane, which is potentially capable to replace parabolic antennas, because it is much more compact than classical solutions and uses a single patch as feeding device. Such structure acts as a metallic photonic crystal at the band edge or as an ultra-refractive metamaterial. A numerical 3D code computing the diffraction by metallic bi-periodic gratings, and a fast layer-by-layer approach, allows to model and to optimize this kind of antennas. Especially, it is reported how both directivity and frequency bandwidth can be improved simultaneously. Numerical results are confirmed by experiments in an anechoic chamber.

On the role of the losses in metamaterials

Contrarily to classic Right-Handed Materials (RHMs), the role of losses is crucial for composite materials called metamaterials such as Ultra-refractive Right-Handed Materials (URHMs) and Left-Handed Materials (LHMs). As the loss-free case for a metamaterial is not stable, a small variation of losses can drastically modify the expected properties of such a material. Thus, it is important to understand how the input of lossy term affects URHM and LHM aspects, and also to define, for each of them, the tolerance level for which the interesting metamaterial properties are still valid. The role of losses is investigated analytically and numerically, a full study about the action of the losses on all the properties is done. It is shown that those properties almost completely disappear for an LHM slab with loss tangent over 0.01, which at optical frequencies corresponds to a good material.

Metallic photonic crystals at RF and at optical frequencies

RF models are frequently used for testing concepts that should finally work at optical frequencies. Since metals loose their conductivity at optical frequencies (OF), such models are of questionable value. In this paper we present simulations of 2D metallic photonic crystals (PhC) consisting of arrays of metallic wires at RF and at OF that show the limitations of RF models.

Compact directive antennas using frequency-selective surfaces (FSS)

This paper presents a theoretical, numerical and experimental study for the design of three-dimensional directive antennas for microwave telecommunications (KU-band: 12-18 GHz) applications. These antennas are resonant cavities surrounded by a metallic ground plane and a metallic grid, which acts as a frequency-selective surface (FSS). These structures are much more compact than classical solutions and use a single feeding device. The development of a numerical 3D code computing the diffraction by periodic metallic gratings allows to model and to optimize this kind of antennas. Numerical results are confirmed by experiments in an anechoic chamber.