L. Le Coq

Millimeter Wave Reconfigurable Antenna Based on Active Printed Array and Inhomogeneous Lens

This paper deals with radiation pattern reconfigurable antenna in millimetre wave range. An active printed antenna array is designed in 24 GHz band and feed an inhomogeneous lens (Half Maxwell Fish Eye) to obtain reconfigurable patterns and in particular sectorial and directive cases. In the first part, the authors describe a four patches multilayer active array which allows achieving radiation pattern control by associating a commutator to each element and by changing the fed patches number. In a second part, this array feed an inhomogeneous lens to shape radiation pattern.

Improvement of the Scanning Performance of the Extended Hemispherical Integrated Lens Antenna Using a Double Lens Focusing System

We demonstrate that an integrated lens antenna (ILA) with a double lens (DL) focusing system can provide simultaneously a high broadside directivity and a low scan loss over a wide angular range. The proposed DL ILA system consists of a hemispherical substrate lens and a planoconvex objective lens. A prototype of a high-gain DL ILA with lenses made of a low permittivity dielectric material is fabricated and characterized in the frequency range of 75-79 GHz. The realized scan loss in terms of gain within a ±30° field of view is <;1.1 dB in both planes. The performance of the DL ILA is compared with that of two hemispherical ILAs designed to provide the best broadside directivity and the lowest scan loss, respectively.

Dielectric resonator antenna reflectarray in Ka-band

A reflectarray antenna combines some of the best features of reflector antennas and phased array antennas [1]. It consists of a primary source illuminating a planar surface composed of many unit-cells. By varying the parameters of each cell, it is possible to control the main beam direction and shape the beam. Many prototypes in microstrip technology have been proposed recently [2,3]. Nevertheless, at millimeter waves, the conductor losses become severe, and the antenna efficiency may drop significantly. On the other hand, dielectric resonator antennas (DRAs) have been introduced due to their low loss, relatively wide bandwidth and high radiation efficiency [4]. Due to these advantages, a first DRA reflectarray was developed in Ka-Band in [5]; in that work, the required phase delay was achieved by varying the DRA length, and the reflectarray was made of DRA blocks of various size. We have introduced recently an alternative solution based on strip-loaded DRAs [6]. In this design, the desired phase delay is only controlled by the length of the metallic strip printed on top of constant-size DRA; this concept has been validated experimentally in C-band in waveguide simulators [6]. In this paper we apply similar ideas in Ka-band (30 GHz), and we present the design and measurement of a complete 24×24-element reflectarray.

Size reduction of synthesized elliptical substrate lenses using air cavities

A new configuration of extended hemispherical lenses with an air cavity above the feed region has been proposed. This technique enables one to achieve the same beam patterns as synthesized elliptical lenses, but with smaller height (10.1%), dielectric loss (15.7%) and weight (13.6%). Various lens configurations fed by printed patch antennas have been designed and compared in Ka-band.

Printed bowtie antenna fed by electromagnetic coupling

Printed planar antennas are widely used in many current applications. One of the main limitations is their narrow bandwidth. To improve this last parameter, several shapes have been studied, namely: bowtie, spiral, logarithmic antennas, ... The investigated results indicate that the radiating performances are influenced, as expected, by the dielectric substrate, the radiating element shape and the feeding circuits. In the present research, printed bowtie antennas fed by electromagnetic coupling from an embedded microstrip line are investigated, An impedance transformer circuit is optimized and the obtained performances are compared to those given by a simple 50 /spl Omega/ microstrip line. Measurements of return loss and radiation patterns are also presented and compared to the calculated ones.

Far field millimetric band antenna test facility : Positioning procedure using phase measurements

Since several years IETR has been conducting active research activities on the modelling and design of millimetric radiating structures and devices. The experimental validation of innovative designs and homemade electromagnetic CAD tools is of uppermost importance. To this end, prototyping capabilities and complementary sets of antenna test facilities at millimetre waves are available for routine experiments (e.g. [18-110] GHz far field chamber, [2-110]GHz coaxial vector network analyser). In such a context, antenna measurements are considered as a key step of the research process. Even though our measurements facilities are not used for certification purposes, they need to provide reproducible, reliable and accurate data for a wide diversity of antenna topologies and dimensions. Then, the definition of the same coordinates system for measurements and simulations remains a sensitive point. We present in this paper an easy-to-use positioning procedure based on phase measurements from Ka-band to W-band. This technique is briefly described in Section 1. Various experimental results are given in Section 2 and conclusion are drawn in section 3..

Small and ultra wide band antennas : A new challenge for characterisation

Research activities on antenna miniaturisation are particularly important to meet systems requirements in terms of compact, integrated antennas including broadband antennas for high data rate communications. IETR has been involved with such a topic for several years. As far as compact and broadband antennas are concerned, one has to deal with specific characterisation issues. Among different factors, the environment effects and the excitation devices are key parameters to consider. This paper focuses on some of these parameters and their influence on gain, impedance or efficiency measurements, and describes some possible solutions to control the reproducibility of these measurements. In this paper we present different hard point we have identified during our measurements. The advantages of some specific test environments such as reverberation chamber and near field test set up was also discussed.

Lens antennas with beam shaping capabilities at the feed level

The performances of focal array fed lenses have been studied for beam diversity applications. We have shown that optimizing the feed sub-arrays enables one to achieve very attractive radiation characteristics without using sophisticated techniques based on shape optimization. A specific and powerful design methodology based on FDTD and GA has been proposed to synthesize reconfigurable integrated lens antenna. It has been validated numerically through the design of several extended hemispherical ILAs producing flat-top and multiple shaped beams.

A stepwise and effective procedure for impedance matching of slot-fed planar antennas. application to the design of wide band printed antennas and reconfigurable EBG resonator antennas

In this paper, the authors propose an effective design methodology for the impedance matching of aperture-coupled microstrip antennas. Our impedance matching method is described in detail in section 1. Then it is applied to design a 20%-bandwidth stacked patch antenna at 7GHz in section 2, as well as a Ku-band reconfigurable EBG resonator antenna with an embedded slot-fed patch antenna and a reconfigurable partially reflecting surface in section 3.

60 GHz electromagnetic fields do not activate stress-sensitive gene expression

The purpose of this study was to determine whether millimeter waves exposure at 60GHz, upcoming to use for indoor high rate communications in local area networks, could lead to a stress response in human brain cells. U-251 MG cell line was sham-exposed or exposed to low power density millimeter radiation for different duration, from 1h to 33h. Using the transfection technique, we analyzed the gene expression for reporter genes previously shown highly sensitive to many environmental insults. We have tested the influence of 60GHz radiations on 3 different gene expression systems, overlaying the main cellular response pathways to physical and chemical stresses. No statistically significant difference was detected in transcriptional activity of reporter genes after radiation exposure. These results suggest that radiation in the frequency range around 60GHz is not a stressor strong enough to modify the stress-sensitive gene expression.