Jean-Yves Dauvignac

Dual-frequency and broad-band antennas with stacked quarter wavelength elements

Original lightweight, low-cost, and compact air-filled planar antennas with short-circuited elements, fed by a coaxial probe, for dual-frequency (S-antenna) and wide-band applications (E-antenna) are investigated. The two-band frequency antenna is formed of two stacked quarter-wavelength elements, short-circuited along diametrically opposed planes. This structure offers two modes with different radiation characteristics. The ratio between the two frequencies can be closely controlled within a range varying from 1.3-2. A bandwidth of 30% for a VSWR <2 is demonstrated using two stacked quarter-wavelength elements short-circuited along the same plane. Numerical simulation results are compared with experiments and a very good agreement is observed. Radiation patterns and input impedance of both structures are measured and the effects of various physical parameters are presented.

An inverse scattering method based on contour deformations by means of a level set method using frequency hopping technique

A shape reconstruction method for electromagnetic tomography based on contour deformations by means of a level set method is proposed. The level set method adds quite valuable features to the inverse procedure such as natural regularization of the contours and automatic breaking and merging capability. The frequency hopping technique turns out to be a key point of the inverse scattering procedure. The numerical results clearly indicate that the use of this inversion algorithm yields to accurate reconstructions of one or several objects from one initial guess object, even with noise-contaminated data and limited coverage of the fields.

94 GHz Folded Fresnel Reflector Using C-Patch Elements

A 94 GHz folded Fresnel reflector (FFR) for helicopter collision avoidance Radar is presented. The antenna system consists of a primary source illuminating a semi-reflecting grid that reflects the primary source polarization toward the main reflector opposite the grid. The main reflector has two functions. It focuses the field in the desired direction and rotates the incident polarization by 90deg to enable it to pass through the grid and radiate. Specific patch elements having a C-shape have been designed for this purpose. In order to increase overall efficiency, the reflector combines 8 correcting zones in its center and 4 at the periphery. The reflector is manufactured using standard photolithographic techniques. The primary source consists of a metal waveguide covered with a small frequency selective surface (FSS) for matching purposes. The maximum measured gain is 36.5 dBi at 94 GHz. The maximum side lobe level is -18 dB. The return loss value does not exceed -25 dB. The frequency bandwidth -3 dB in gain and return loss is 10%. In-flight measurements were conducted demonstrating the ability to detect power lines at distances up to 680 m.

Performance of obstacle detection and collision warning system for civil helicopters

Some helicopters strike the power lines under the good weather conditions. Helicopter pilots sometimes have some difficulties to find such long and thin obstacles. We are developing an obstacle detection and collision warning system for civil helicopters in order to solve such problems. A color camera, an Infrared (IR) camera and a Millimeter Wave (MMW) radar are employed as sensors. This paper describes the results of different flight tests that show good enhancement of radar detection over 800m range for power lines. Additionally, we exhibit the processed fusion images that can assist the pilots in order to recognize the danger of the power lines.

Time‐domain processing of electromagnetic data for multiple‐target detection

This research represents a synthesis of ultra‐wideband antenna hardware, employed for multiple target detection, using time‐reversal processing and the decomposition of the time‐reversal operator to obtain target location. Real‐data examples are presented using a symmetric and asymmetric configuration consisting of two scatterers. A new entropy‐based criterion for stopping the time‐reverse sequence is employed.

Recent nonlinear inversion methods and measurement system for microwave imaging

The paper reviews different inversion methods in connection with different measurement systems to solve nonlinear inverse scattering problems for various applications where the discrepancy between the measured and computed scattered field is minimized at each step of an iterative procedure. First, the reconstruction of the complex permittivity profile (permittivity and conductivity profiles) of inhomogeneous buried objects using polarization diversity (TM, TE and cascaded TE-TM polarizations) is considered for nondestructive testing, geophysical, civil engineering, or humanitarian applications. Second, a boundary-oriented method based on contour deformations is exposed for reconstructing the shape of metallic objects for radar imaging purposes.

Real data microwave imaging and time reversal

The development of SIMIS (Synthetic Impulse Microwave Imaging System), a microwave array of eight ultra-wideband Vivaldi-type ETSA antennas, employed to image unknown targets situated in an anechoic chamber, is presented. Real scattering data, collected via an RF multiplexer interfaced to a vector network analyzer, is imaged using the Time Reversal Method. The imaging algorithm is applied to the scattered field from a dielectric cylinder. In addition, real data is presented for the same dielectric cylinder, located behind a vertical wall.

Design Optimization of UWB Printed Antenna for Omnidirectional Pulse Radiation

The use of ultrawideband technology in many applications implies the use of a suitable radiating structure, especially for pulsed systems. The development of a triangular CPW-fed printed antenna with specific ground plane shape is presented. First the triangular element was optimized to minimize return losses and size of the antenna in the [3.1-10.6] frequency band. The evolution of radiation patterns with frequency was also studied, as changes in phase center position and radiation characteristics alter the integrity of transmitted pulses. Thus the antenna ground plane shape was modified in order to maintain almost constant radiation patterns over the entire bandwidth. Time domain measurement methods were used to characterize the antennas and validate these improvements. The procedure is presented and results are plotted in a 3D format and discussed.

Development of Antennas for Subsurface Radars within ACE

The paper gives an overview of the joint activities of the ACE-2 partners in the area of antennas for surface penetrating radar. Main areas of joint research and development are discussed and main results of joint activities are presented. Special attention is given to experimental verification of proposed antenna designs.

76.5 GHz millimeter-wave radar for foreign objects debris detection on airport runways

The paper is a joint work between the LEAT (France) and the ENRI (Japan) in the framework of a Sakura project supported by the JSPS and the French Ministry of Foreign Affairs. The purpose is the study of a FOD (Foreign Object Debris) detection system on airport runways. A FM-CW mm-Wave radar working between 76.25 and 76.75 GHz is used together with a high directivity printed reflectarray. Measurement results show detection capabilities of a -20 tlBsm cylinder up to 35 m which is 10 m less than the FAA recommendations. Antenna improvements are discussed for reaching the requirements and system performance as well as the use of calibration objects.