A wideband high-gain terahertz dielectric reflectarray working at 220 GHz is investigated both theoretically and experimentally. The reflectarray unit cell consists of a ground plane and a dielectric block. The reflection phase is obtained by adjusting the height of the block. Using the reflection phase computational algorithm, a dielectric reflectarray composed of 40 × 40 unit cells is designed and fabricated through three-dimensional (3-D) printed technology. Four types of 3-D printed material are measured using the THz time-domain spectroscopy system. It is found that the maximum gain and gain bandwidth of the proposed reflectarray is 31.3 dBi and 20.9%, respectively. Measured results are in reasonable agreement with simulated results. This result is an important step toward the 3-D printed THz dielectric reflectarray above 220 GHz.

In this paper, a reconfigurable reflectarray operating at 220 GHz based on the simple patch element has been designed. The element can provide two states with a phase difference of 180°, by controlling the connection between ground and patch. To implement the reconfigurable performance, the PIN diode has been integrated in the unit. A $15 \times 15$ reconfigurable reflectarray (RRA) prototype has been designed. It can realize beam scanning in the range of 0°-50° with the maximum gain of 21 dBi and the aperture efficiency of 43.7% at 220GHz.

This paper investigates the performance of a wide variety of radar imaging modes, such as nadir-looking B-scan, or side-looking synthetic aperture radar tomographic acquisitions, performed in both back- and forward-scattering geometries, for the inspection and characterization of roadways. Nadir-looking B-scan corresponds to a low-complexity mode exploiting the direct return from the response, whereas side-looking configurations allow the utilization of angular and polarimetric diversity in order to analyze advanced features. The main objective of this paper is to evaluate the ability of each configuration, independently of aspects related to operational implementation, to discriminate and localize shallow underground defects in the wearing course of roadways, and to estimate key geophysical parameters, such as roughness and dielectric permittivity. Campaign measurements are conducted using short-range radar stepped-frequency continuous-waveform (SFCW) devices operated in the C and X bands, at the pavement fatigue carousel of Université Gustave Eiffel, over debonded areas with artificial defects. The results indicate the great potential of the newly proposed forward-scattering tomographic configuration for detecting slight defects and characterizing roadways. Case studies, performed in the presence of narrow horizontal heterogeneities which cannot be detected using classical B-scan, show that both the coherent integration along an aperture using the back-projection algorithm, and the exploitation of scattering mechanisms specific to the forward-looking bistatic geometry, allows anomalous echoes to be detected and further characterized, confirming the efficacy of radar imaging techniques in such applications.

There is great necessity to allocate/combine the power of signal in the present 340GHz microwave system. Therefore, this paper designed a 340GHz directional coupler with branch waveguide structure. A five-branch waveguide structure was designed in this paper considering relative bandwidth and the size of the structure. After simulating and analyzing the model of coupling structure by finite element method, we got the result that it can realize 3dB coupling during 325GHz~352GHz, while the flatness is less than 0.16dB. The phase difference of two output ports is 120 degrees.

Several wideband millimeter-wave dielectric reflectarray antennas are discussed in this paper. Different phase distributions are realized by changing the shape or material of the array element. Three dielectric reflectarray of 20×20 elements operating at 100GHz are compared. The 1dB gain bandwidths of the dielectric reflectarray are larger than 10% and up to 40%. As compared to the microstrip reflectarray, the dielectric reflectarray can reduce the metal losses and effectively improve the gain bandwidth.

Techniques d'imagerie radar pour la caractérisation et le diagnostic des chaussées: Ce travail concerne l'imagerie tomographique 3-D par Radar à Synthèse d'Ouverture de terrain (GB-SAR) pour la détection in situ des défauts de chaussée.Un GB-SAR bistatique à visée latérale, fonctionnant en mode de propagation vers l'avant (FSC), caractérisé par un rapport Signal sur Bruit (SNR) élevé et une résolution verticale constante, est proposé. Une focalisation tomographique utilisant une ouverture dans la direction verticale est introduite pour résoudre l'ambiguïté et améliorer la résolution en distance au sol. Une configuration SAR bistatique FSC à déplacement horizontal et à décalage constant (COSBis), est proposée afin de réduire la complexité du système à un niveau minimal, en utilisant une seule paire d'antennes Tx et Rx, et qui permet d'obtenir une résolution en distance au sol améliorée par focalisation sur une ouverture angulaire générée par le mouvement horizontal. Les résultats expérimentaux démontrent la capacité du mode proposé à détecter des défauts artificiels et à caractériser des détails fins en utilisant une diversité de polarisation. Des techniques d'analyse spectrale à haute résolution sont appliquées à l'approche COSBis pour affiner le diagnostic routier. Cette configuration innovante de GB-SAR, associée à des techniques d'imagerie à haute résolution, démontre un fort potentiel pour l'inspection et la maintenance des chaussées.