Ettien Lazare Kpré

CLEAN Deconvolution Applied to Passive Compressed Beamforming

In this article, a matching pursuit algorithm is developed to improve the performance of a passive multiplexing technique based on compressed sensing. This deconvolution technique is applied to RADAR imaging in the microwave range, starting from previous studies based on a compact coding device and L 1 -norm regularizations. This study demonstrates that in this context, the quality of the reconstructed RADAR images can be improved using an algorithm close to Hogboms Clean, and based on a dictionary built with Tikhonov pseudo-inversions. The theoretical principle of this new algorithm is developed, followed by a parameters study. Finally, an experimental validation is presented to demonstrate the efficiency of this iterative algorithm.

Passive compression technique applied to UWB beamforming and imaging architectures

Recent works have demonstrated the feasibility of microwave imaging using compressive techniques, exempting the use of active delay lines, phase shifters, or moving parts to achieve beamforming. With this method, waves are coded in a passive way by a compressive device to reduce the complexity of the transmitter and/or receiver chains of the telecommunication and radar systems requiring beamsteering. Such a technique is based on the exploitation of the frequency diversity, implying that a reduction of the compressive devices volume imposes a diminution of the number of driven antennas. In this paper, the improvement brought by simultaneous excitations of the compressive device is presented. Adapting a new mathematical formulation, it is shown that M inputs can send independent waveforms allowing the beamsteering of an N-elements antenna array, while maintaining N > M.

Passive Coding Technique Applied to Synthetic Aperture Interferometric Radiometer

For real-time and high-resolution radiometric imaging, the synthetic aperture interferometric radiometer (SAIR) technique seems to solve the tradeoff between imaging resolution and aperture size. Indeed, it can synthesize a large antenna array by sparsely arranging a small number of antennas to achieve high spatial resolution. Nevertheless, a conventional interferometric radiometer requires as many receivers as antennas needed. This constraint is one of the limitations of SAIR regarding the hardware cost, the system complexity, and the computation load. In this letter, a compressed acquisition technique is proposed to collect the antenna signals. In this method, the antenna’s signals are coded and combined red with a passive microwave device. From the measured waveforms at the receiver’s outputs, a decoding process is performed to estimate the received signal by each antenna. This allows the computation of the visibility function required for image reconstruction. The effectiveness of the proposed method has been tested by means of simulations analysis and has experimentally been applied to a punctual noise source detection. The results reveal that this method can be an efficient alternative for the simplification of the conventional interferometric radiometers’ architectures.

Synthetic aperture interferometric imaging using a passive microwave coding device

There has been growing interest in the use of microwave synthetic aperture radiometers since their could solve the trade-off between the image resolution and the antennas aperture size. Compared to classical techniques, SAIR (Synthetic Aperture Interferometric Radiometer) can reach a large field of view (FOV) and high imaging rate. Nevertheless, the architecture of a conventional radiometer still bulky and costly. In this paper, a passive combining technique is proposed to reduce the hardware complexity as well as the dimensional requirements of the receiving antennas. Experimental results are presented to highlight the effectiveness of the proposed technique.

Millimeter wave computational interferometric radiometer

This work is focused on the conception of a new kind of mm-wave radiometer based on a computational imaging technique. The aim is the design of a radiating aperture associated with a dispersive component able to passively multiplex the received signals, allowing for a massive simplification of the active part in comparison with conventional solutions. This approach also requires the implementation of fast algorithms for retrieving the coded signals and reconstruct images of the target, desirably at the speed of several frames per second.