Cyril Decroze

Computational imaging using a mode-mixing cavity at microwave frequencies

We present a 3D computational imaging system based on a mode-mixing cavity at microwave frequencies. The core component of this system is an electrically large rectangular cavity with one corner re-shaped to catalyze mode mixing, often called a Sinai Billiard. The front side of the cavity is perforated with a grid of periodic apertures that sample the cavity modes and project them into the imaging scene. The radiated fields are scattered by the scene and are measured by low gain probe antennas. The complex radiation patterns generated by the cavity thus encode the scene information onto a set of frequency modes. Assuming the first Born approximation for scattering dynamics, the received signal is processed using computational methods to reconstruct a 3D image of the scene with resolution determined by the diffraction limit. The proposed mode-mixing cavity is simple to fabricate, exhibits low losses, and can generate highly diverse measurement modes. The imaging system demonstrated in this letter can find application in security screening and medical diagnostic imaging.

Compact and Multiband Dielectric Resonator Antenna With Pattern Diversity for Multistandard Mobile Handheld Devices

A compact multiband antenna system using a dielectric resonator antenna (DRA) is presented in this paper. Designed to be integrated in a tablet, it is not only heavily miniaturized (λ0/15×λ0/38×λ0/94 at 800 MHz), but also able to cover three frequency bands for different wireless applications (DVB-H, WiFi and WiMAX). Since a reconfigurable radiation pattern can result in an improved quality and reliability of wireless links, two DRAs have been integrated to implement this feature on the three frequency bands. These improvements are demonstrated by the presentation of the correlation coefficient and the effective diversity gain, both measured in a reverberation chamber. The experimental measurements are in very good agreement with the simulated ones. Good overall performances are obtained, and the requirements of all three applications are perfectly met. Moreover, the antenna operative frequencies are independent of the ground plane dimensions, making this system a very good candidate for all kinds of mobile devices.

Frequency Tunable Antenna Using a Magneto-Dielectric Material for DVB-H Application

This paper presents an ultracompact antenna design suited for digital video broadcasting-handheld (DVB-H) reception devices. The DVB-H frequency band is ranging from 4 70 to 862 MHz and divided in 49 channels of 8 MHz. Designed to be integrated in a tablet, it is not only heavily miniaturized (λ0 /49 × λ0/71 ×λ0/160 at 470 MHz), but also able to cover each channel thanks to the use of a magneto-dielectric material. The advantage of using such a material is studied and described in this paper. Moreover, the operating frequency is continuously tuned over the whole DVB-H band by the integration of a varactor diode. This varactor diode has been characterized and modeled to properly cosimulate its behavior within the antenna. Limitations in terms of accepted power by the diode are emphasizing. Finally, the antenna design, including both magneto-dielectric material and varactor diode is integrated in the DVB-H receiver device. Measurement performances are presented and discussed.

UWB Antennas Beamforming Using Passive Time-Reversal Device

In this letter, the feasibility of a new concept of passive antenna beamformer is investigated. The main idea is to develop a (1×N)-ports device in which the weightings on output ports are applied by time-reversal operation. The control of antennas weightings is then contained in the input waveform without the need of active components or external control signals. This approach is validated experimentally by radiation pattern measurement of a four-Vivaldi-antennas array, associated to a small reverberation cell beamformer. Finally, this concept is applied to realize a passive ultrawideband (UWB) phased-array radar for target imaging.

3GPP Channel Model Emulation with Analysis of MIMO-LTE Performances in Reverberation Chamber

Emulation methodology of multiple clusters channels for evaluating wireless communication devices over-the-air (OTA) performance is investigated. This methodology has been used along with the implementation of the SIMO LTE standard. It consists of evaluating effective diversity gain (EDG) level of SIMO LTE-OFDM system for different channel models according to the received power by establishing an active link between the transmitter and the receiver. The measurement process is set up in a Reverberation Chamber (RC). The obtained results are compared to the reference case of single input-single output (SISO) in order to evaluate the real improvement attained by the implemented system.

Ultrawideband Dielectric Resonator Antenna for DVB-H and GSM Applications

This letter presents a novel design of compact dielectric resonator antenna (DRA) that is dedicated to ultrawideband applications such as digital video broadcasting-handheld (DVB-H). The dimensions of the radiation element are lambda0/7 times lambda0/13 times lambda0/28 at 466 MHz. A miniaturization technique has been used in order to reduce the antenna size, and a parametric analysis of the antenna is performed. The measured results agree well with the simulated ones. The proposed antenna offers a bandwidth of 70% around 700 MHz for -8 dB impedance matching bandwidth definition and covers the Ultra High Frequency (UHF) IV, V and Global System for Mobile communications (GSM) bands.

Single-Shot Compressive Multiple-Inputs Multiple-Outputs Radar Imaging Using a Two-Port Passive Device

This paper presents a compressive technique that simplifies the architecture of multiple-input multiple-output (MIMO) radar imaging systems. By means of a passive device connected to an MIMO array of antennae, a novel approach is introduced to extract the interaction between antennae from a compressed signal measured between two ports. This technique relies on a multiplexing principle that exploits the frequency diversity and it is thus particularly suitable for ultrawideband imaging systems. This paper presents the theoretical principle underlying this compressive technique, defining the key parameters affecting the information retrieval from a measured frequency signal and the prior characterization of the compressive devices transfer functions. Simulations are performed to demonstrate the potential of the technique for MIMO ultrawideband imaging systems and its compatibility with fast range migration algorithms based on fast Fourier transforms. Finally, an experimental validation is performed with a two-dimensional radiating aperture connected to a compressive device, allowing for the three-dimensional near-field imaging of different targets.

Waveform Coding for Passive Multiplexing: Application to Microwave Imaging

This paper proposes a novel passive technique for the collection of microwave images. A compact component is developed that passively codes and sums the waves received by an antenna array to which it is connected, and produces a unique signal that contains all of the scene information. This technique of passive multiplexing simplifies the microwave reception chains for radar and beamforming systems (whose complexity and cost highly increase with the number of antennas) and does not require any active elements to achieve beamsteering. The preservation of the waveforms is ensured using orthogonal codes supplied by the propagation through the components uncorrelated channels. Here we show a multiplexing technique in the physical layer that, besides being compact and passive, is compatible with all ultrawideband antennas, enabling its implementation in various fields.

A New CLEAN Algorithm for Angle of Arrival Denoising

In a previous work, a novel technique for angle of arrival (AOA) measurement was proposed. This technique consists of sweeping the angular domain with one antenna, step by step, such that at each measurement step the received signal voltage at the rotating antenna (sensor) is measured. The signal voltage vector is the convolution between the antenna electric field pattern and the AOAs (magnitude and phase) of the incident wave. In this letter, a denoising CLEAN algorithm is modified and applied to this technique in order to eliminate spurious peaks and accurately find the AOAs of incoming waves. A set of measurements is made to evaluate the proposed algorithm. The results show the effectiveness of the denoising algorithm in reducing the noise level; a high angular precision in measured AOAs is noticed.

A simple technique for angle of arrival measurement

A simple method to calculate the angle of arrival is presented in this paper. The advantages of this method are the unlimited number of the detected angle of arrival in hand and the fact that we donpsilat need to know the nature of the radiating sources in the other hand. However, some disadvantages have been seen. Firstly a positioning system is indispensable to rotate the sensor and secondly, the propagation channel must be stable during the sensor rotation.