Frédéric Bongard

Experimental verification of broadband cloaking using a volumetric cloak composed of periodically stacked cylindrical transmission-line networks

Cloaking using a volumetric structure composed of stacked two-dimensional transmission-line networks is verified with numerical simulations and measurements. The measurements are done in a waveguide, in which an array of metal cylinders is inserted causing a short circuit in the waveguide. The metal cylinders are cloaked using the transmission-line structure, which “hides” the cylinders and thus enables wave propagation inside the waveguide.

Integral-Equation Analysis of 3-D Metallic Objects Arranged in 2-D Lattices Using the Ewald Transformation

We present a space-domain integral-equation method for the analysis of periodic structures formed by three-dimensional (3-D) metallic objects arranged in a general skewed two-dimensional lattice. The computation of the space-domain Greens function is accelerated using the Ewald transformation. The method is validated on several periodic structures ranging from planar frequency-selective surfaces to 3-D photonic crystals and metamaterials. For these structures, our technique shows a clear advantage in terms of computational speed when compared with available commercial softwares

Sparse Array Antenna for Ku-Band Mobile Terminals Using 1 Bit Phase Controls

This paper presents a new architecture for low-cost mobile terminal antennas suitable for linear-polarized satellite communications systems. It is based on a sparse phased array that uses 1-bit phase controls. In this way it is possible to reduce the array cost by employing simpler and fewer controls. Measurements of a prototype demonstrate the feasibility of the approach.

Broadband cloaking of selected objects in the microwave regime with a volumetric cloak comprising layered networks of transmission lines

A volumetric cloak composed of cylindrical two-dimensional transmission-line networks, has been studied with numerical simulations and measurements. The broadband cloaking effect obtained with this structure is confirmed for two different metallic objects.

A New Aperture for Switched-Beam Low-Profile Ku-Band Mobile Terminal Array Antennas [EurAAP Corner]

This paper presents an innovative switched-beam architecture for a low-cost mobile-terminal antenna, suitable for linear-polarized satellite communications systems. This antenna concept can produce twelve adjacent sector beams that cover the full azimuth field of view with a directivity of 11 dB, using the same physical aperture. This radiating aperture consists of slot-coupled patch antennas arranged in a specific lattice, inspired by the so-called tri-hexagonal tiling of the plane. An innovative beamforming-network layout, based on series feeding, is devised to reduce the circuit-board real estate required by the different beams. A prototype producing two beams has been built, and its radiation pattern has been measured, in order to demonstrate the feasibility of the approach.

Low-profile tunable radiator for small satellite application

A tunable radiator for space application has been developed to meet stringent requirements in terms of electrical and environmental specifications but also low mass, simple manufacturing and low cost. The element is based on the folded planar inverted F-antenna, with size of one quarter of wavelength. It is mechanically tunable to adjust input impedance for any various positions on the satellite body and possible obstacles and protrusions. Results in terms of radiation pattern, S parameters, shock and vibration tests are presented. The antenna operates in ultra-high frequency band (400 MHz) in linear polarization. It has been designed to act as the basic element for miniaturized multi-function antenna systems on board of small satellites that can operate in three different radiating modes and in both left and right hand circular polarizations.

Transmission line based metamaterials for acoustic waves

We present our recent work on a one-dimensional acoustic negative refractive index metamaterial based on the concept of dual transmission line extensively investigated in microwave engineering. The proposed structure consists of an acoustic waveguide periodically loaded with membranes realizing the function of series “capacitances” and transversally connected open channels realizing shunt “inductances”. It exhibits a negative refractive index band over almost one octave, from 0.6 to 1 kHz. Using formal analogies, we describe how simple acoustic circuit models can be used for efficient design of metamaterials both in terms of dispersion and impedance.

Characterization of metamaterial slabs in terms of scattering parameters under oblique plane wave incidence

In this work, a retrieval procedure which allows the determination of equivalent dyadic permittivity and permeability of metamaterials from reflection and transmission coefficients obtained for several incidence directions and polarizations is presented. The main goal is to determine to which extent a model of anisotropic homogeneous material can be applied to specific metamaterials. Preliminary results on wire media and arrays of magnetic resonators show that a certain level of symmetry in the unit cell is required to avoid bianisotropy, and that small unit cells compared to the wavelength are favorable for such a homogenization.