David Carsenat

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.

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.

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.

Triband Compact Antenna for Multistandard Terminals and User's Hand Effect

A novel compact wideband triband antenna for mobile terminals based on PIFA element is proposed. The antenna operates at the following frequency bands: Wireless-LAN 802.11 b, g, a and WiMAX 3.5 GHz. The antenna was studied by means of numerical simulations as well as the ground plane dimensions and users hand effects. The overall size of the radiating element which is 1.8×1.54×9 mm makes it suitable for use in terminals and appropriate to integrated as an internal laptop antenna. The measured bandwidths show that the proposed antenna can cover three bands (2.39–2.48 GHz), (3.36–3.76 GHz), and (4.7–6.3 GHz) and the total efficiency is better than 90%. The radiation patterns of the antenna were carried in an anechoic chamber and are given to demonstrate the antennas performance.

Antenna Radiation Pattern Measurements in Reverberation Chamber Using Plane Wave Decomposition

Reverberation chambers (RCs) are electrically large, highly conductive resonant enclosures used as test facilities for radiated emissions and immunity measurements on electronic devices. In recent literature, it has been claimed that RCs can be an interesting alternative to anechoic chambers as facilities for accurately characterizing the radiation pattern of an antenna under test, but this assertion has only been supported by numerical simulations, using elementary dipoles in a scalar two-dimensional RC. On the contrary, in this contribution, a novel technique that allows for the first time to perform actual antenna radiation pattern measurements in RC is presented. In order to demonstrate its validity, the radiation pattern for both E- and H- planes of a horn antenna has been measured in an RC at 10 GHz, in X band, and compared to the ones obtained in anechoic chamber, being the results in good agreement.

Antenna Gain and Radiation Pattern Measurements in Reverberation Chamber Using Doppler Effect

In a recent paper, a novel technique that allows for the first time to perform actual antenna radiation pattern measurements in reverberation chamber (RC) has been presented. Even though its results were in good agreement with the ones obtained in anechoic chamber (AC), it was necessary to repeat stationary measurements locating the antenna under test (AUT) at N different fixed positions along its line-of-sight to a fixed probe antenna per angle under study, thus multiplying by N the measurement time when compared to measuring in AC. On the contrary, in this contribution, an improvement of this technique is presented, obtaining an antenna radiation pattern by performing only one measurement per angle under study, taking advantage of real-time Doppler effect. Moreover, the antenna gain is obtained from only one of these measurements, without the need to know the antenna efficiency, by using the Friis transmission equation. In order to demonstrate the validity of this improved technique, the radiation pattern for both E- and H- planes and the gain of a horn antenna have been measured in an RC, being the results in good agreement with the ones obtained in AC and the values provided by the antenna manufacturer, respectively.

UWB passive beamforming for large antenna arrays

A passive technique is developed in this paper to achieve UWB beamforming using a 1 × N device able to code the waves received and transmitted by an antenna array, preventing the use of phase shifters, delay lines, or moving parts. The link between the array inter-element space and the beamforming performance is studied to show the possible application of this device for far-field high resolution beamforming, achieved in a passive way.