Presentation
The HIPE team develops and exploits several measurement apparatuses in the
hyperfrequency regime. These setups permit one to measure:
- active components: antennas, RCS, ...
- passive components; scattering,
dielectric characterization.
The achievable measurements are tightly linked to the
geometrical features of the
available setups.
- a large anechoic chamber with a
spherical geometry, - a small anechoic chamber with a planar
configuration, - a metallic cavity with circular cross-section,
- and cylindrical coaxial cells.
The large anechoic chamber
The experiments are carried out in the anechoic chamber of the Centre Commun de Ressources Micro-Ondes (CCRM)
(CCRM),
managed for this topic by the researchers of Institut Fresnel in Marseille France. The experimental set-up consists of a large faradized anechoic chamber with 14.50 m long, 6.50 m wide, and 6.50 m high, which allows to simply model all the propagation phenomena as free space ones. Its main specificity consists in a semi-circular vertical arch along which two wagons are able to move. The main applications are:
- radar cross section,
- spherical scattering patterns,
- spherical near-field and far-field antennas
measurements.
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| Large anechoic chamber |
A large variety of experimental configurations can be studied, thanks to five mechanical positioners. The first positioner permits to adjust the orientation of the target which is positioned at the center of the set-up on an expanded polystyrene arm. The second positioner controls the antenna which is placed on an arm rotating around the vertical axis within the azimuthal plane. The third and fourth ones are displacing the antenna which are fixed on two wagons which can move along the arch. Both the azimuthal arm and the trail have a 2 m radius. Finally, the fifth positioner, placed at 10.5 m from the target is devoted to RCS measurements.
The available frequency range is from 700 MHz to 26 GHz. All the measurements are performed with a vector network analyzer (Agilent HP 8530) used in a multi-source set-up with two synthetizers and two external mixers. All the mechanical movements and the network analyzer are controlled and synchronized thanks to a PC and a C++ monitoring software.
This chamber has been used for example to provide the scattered fields
of the Fresnel database for
inverse problems applications, both for two-dimensional and three-dimensional
complex targets.
It is currently used to measure the scattering pattern of soot particles
(ANR SOOT).
Small
anechoic chamber
In collaboration with the studies performed in the large anechoic chamber,
we are developing a new setup. It is constituted of an anechoic chamber
(a cube of roughly 3m side), of antennas positioners (horizontal displacement on a 2.50 mx2.50 m squared area and with rotations in order to change the antennas orientations), and a network analyzer which can work up to 40 GHz.
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| Small anechoic chamber |
This configuration enables to position antennas in air above the investigation area, for example a tank of reconstituted soil. Several types of antennas as well as several types of experimental configuration will be tested in order to define the optimal setups for the envisaged applications. In particular,
this setup is used for the control of soil moisture (ANR CESAR). It will also be exploited for the detection and
characterization of buried targets, or for near-field antennas measurements.
This anechoic chamber has been financed thanks to
the University of Provence , the University Paul Cézanne, the CNRS, Marseille town council, the Regional Council of Bouches du Rhone and the State province Council of Provence-Alpes-Cote-d’Azur.
Circular scanner
This setup consists in an array of 64 biconical antennas which are designed to radiate in water at 434 MHz. It is coupled to a multiplexer/demultiplexer device which enables to select any kind of antenna emitter/receiver couple and which can work up to 2 GHz. The antennas are positioned on a ring within a metallic cylinder of 60cm diameter. This metallic casing enables to model the reflexions at the boundaries and prevents parasitic reflexions fro the surroundings. The various transmission coefficients between the antenna pairs are measured thanks to a network analyzer synchronized with a PC. All the transmission coefficients are then entered into inversion algorithms.
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| Circular scanner |
As it can be seen in the previous picture, a column of reconstructed soil can be placed within the circular scanner in order to measure its scattered field for various water content configurations.
This setup has been first developped at Laboratoire des Signaux et Systèmes
for biomedical applications and has been transfered to Institut Fresnel in 2002.
It is now exploited in the ANR CESAR project.
EpsiMu cells
We are also developing measurement tools in order to characterize solid or granular materials in terms of permittivity and permeability values. These measurements are performed thanks to coaxial cells wherein the sample is placed. By measuring the reflexion and transmission coefficients inside the waveguide, it is possible to retrieve the intrinsic dielectrical characteristics of the sample on a large frequency band, from 1 GHz to 18 GHz.
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| Two EpsiMu cells |
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