Larbi Talbi

Novel butler matrix using CPW multilayer technology

In this paper, a novel 4 times 4 two-layer Butler matrix based on a broad-band two-layer slot-coupled directional coupler is presented and implemented at 5.8 GHz using coplanar waveguide technology. With the slot-coupled directional coupler, the proposed matrix was designed without using any crossovers as used in conventional Butler matrices, which leads to significant size reduction and loss minimization. To examine the performance of the proposed matrix, experimental prototypes of the multilayer directional coupler and the Butler matrix were fabricated and measured. Furthermore, a four-antenna array was also designed and fabricated at 5.8 GHz and then connected to the matrix to form a beamforming antenna system. As a result, four orthogonal beams at -45deg, -15deg, 15deg, and 45deg are produced. Measured results on the entire system agree well with the theoretical predictions, validating the proposed design

Analysis and design of a cylindrical EBG-based directive antenna

In this paper, a cylindrical electromagnetic bandgap (CEBG) structure composed of infinite metallic wires is analyzed, designed and used as a model to develop a new reconfigurable directive antenna. This structure is circularly and radially periodic, and it is excited at its center using an omnidirectional source. The analysis is based on calculating the transmission and reflection coefficients of a single cylindrical frequency selective surface (FSS) and then, considering only the fundamental mode interaction, deducing the frequency response of the CEBG structure composed of multiple cylindrical FSSs. For this structure, new analytical formulas are derived, and their accuracy is assessed compared to those obtained by the finite-difference time-domain method. As in rectangularly periodic structure case, the frequency response of the CEBG structure exhibits pass-bands and bandgaps, and it is possible to obtain directive beams by introducing defects in the periodic structure. Using this concept, a new antenna was developed to obtain a controllable directive beam. An antenna prototype, without control, was designed, fabricated, and tested. An excellent agreement was obtained between theory and experiment for both return loss and radiation patterns.

A Conducting Cylinder for Modeling Human Body Presence in Indoor Propagation Channel

We demonstrate that in indoor radio propagation modeling, the presence of the human body may be approximated by a conducting circular cylinder at microwave frequencies. Therefore, a perfect tool such as the uniform theory of diffraction may be used to predict the diffracted field over a smooth circular surface. To validate the model, vertically and horizontally polarized continuous wave (CW) measurements were performed at 10.5 GHz between two fixed terminals inside a room along with the presence of an obstacle (person or metallic cylinder) moving along predetermined parallel and perpendicularly crossing paths with respect to the line-of-sight direction. Results indicate that there is a strong correlation between the effects of the human body and those of a conducting circular cylinder. The simulation results successfully agree with the CW experimental measurements.

Wideband Fabry-Perot Resonator Antenna With Two Complementary FSS Layers

This paper presents a novel design of a Fabry-Perot (FP) resonator antenna with a wide gain bandwidth in X band. The bandwidth enhancement of the antenna is attributed to the positive reflection phase gradient of an electromagnetic band gap (EBG) structure, which is constructed by the combination of two complementary frequency selective surfaces (FSSs). To explain well the design procedure and approach, the EBG structure is modeled as an equivalent circuit and analyzed using the Smith Chart. Experimental results show that the antenna possesses a relative 3 dB gain bandwidth of 28%, from 8.6 GHz to 11.4 GHz, with a peak gain of 13.8 dBi. Moreover, the gain bandwidth can be well covered by the impedance bandwidth for the reflection coefficient ( S 11) below -10 dB from 8.6 GHz to 11.2 GHz.

Experimental Characterization of an UWB Propagation Channel in Underground Mines

An experimental characterization of the ultrawideband (UWB) propagation channel in an underground mine environment over the frequency range from 3 GHz to 10 GHz is reported in this paper. Two kinds of antennas, directional and omnidirectional, were used to investigate the effect of the antenna directivity on the path loss propagation and on the time dispersion parameters in both line-of-sight (LOS) and no-line-of-sight (NLOS) underground galleries. The measurement and simulation results show that the path loss exponents in an underground environment are larger than their counterparts in an indoor environment. In NLOS, the directional-directional (Direct-Direct) antenna combination showed better radiation efficiency for reducing the time dispersion parameters while the omnidirectional-omni directional (Omni-Omni) case resulted better performance in term of path loss. After extracting the channel parameters, a statistical modeling of the UWB underground channel based on data measurements was conducted.

MIMO-UWB Channel Characterization Within an Underground Mine Gallery

Multiple input multiple output-ultrawide band (MIMO-UWB) systems are experimentally evaluated for underground mine high-speed radio communications. Measurement campaigns using two different antenna configurations have been made in an underground gold mine. Furthermore, two scenarios, which are the line of sight (LoS) and the non-LoS (NLoS), i.e., taking into account the mining machinery effect, are distinguished and studied separately. In fact, the channel is characterized in terms of coherence bandwidth, path loss, shadowing, channel correlation, and capacity. Results reveal how antenna array configuration affects main channel parameters and suggest that mining machinery presence substantially affects both received power and time dispersion parameters within the underground mine and should, therefore, be considered when assessing the performance of in-gallery wireless systems. Moreover, it is shown that the MIMO-UWB takes benefit of the large spreading bandwidth and the multipath propagation environment to increase the channel capacity.

Design of a Broadband Hybrid Dielectric Resonator Antenna for X-band Applications

In this paper, a new design of a broadband hybrid antenna for X-band applications is presented. The proposed antenna structure consists of a Dielectric Resonator (DR), an intermediate substrate, and a microstrip fed slot. With the integration of these elements, a wide bandwidth response was achieved. A dual-offset feedline is used to further tune the impedance bandwidth. High Frequency Structure Simulation (HFSS) software package of Ansoft is used to investigate the antenna performance. The input impedance and the far-field patterns were performed out, and a parametric study was done to optimize the antenna performance. The proposed antenna was then fabricated and measured. A good agreement between simulated and measured results was obtained. Experimental results show that the proposed antenna exhibits a wide input impedance bandwidth of 59.1%.

Wideband Fabry–Perot Resonator Antenna With Two Layers of Dielectric Superstrates

This letter presents a new design of a Fabry-Perot resonator antenna (FPRA) with a wide gain bandwidth. A double-layered dielectric superstrate, which produces a reflection phase curve versus frequency with a positive slope, is used as a partially reflective surface (PRS) to enhance the bandwidth of the FPRA. For a physical insight, the PRS is analyzed by using the transmission line theory and Smith Chart. Experimental results demonstrate that the antenna has a 3-dB gain bandwidth over 13.5-17.5 GHz, relatively 25.8%, with a peak gain of 15 dBi. Furthermore, the gain band is overlapped well by the impedance band for the reflection coefficient ( S11) less than -10 dB.

Modeling human body effects for indoor radio channel using UTD

In this paper, a practical deterministic propagation prediction model is introduced to investigate the human body-scattering effects in the indoor channel using the uniform geometrical theory of diffraction (UTD). In the model, the human body is approximated with a perfect conducting circular cylinder and then combined with the ray-tracing technique to deal with particular indoor propagation scenarios. By maintaining both the transmitter and the receiver at fixed positions, we investigated the nature of propagation due to the movement of the cylinder in a predetermined parallel path with respect to the line-of-sight (LOS) path between the transmitter and receiver. In order to validate the developed model, continuous wave (CW) experimental measurements are conducted and have successfully fitted the predicted data. Results also indicate that reflections onto persons are significant and will have to be considered in developing a full deterministic model of the indoor propagation channel.

Novel Butler matrix using CPW multi-layer technology

In this paper, a novel 4 times 4 two-layer Butler matrix based on a broad-band two-layer slot-coupled directional coupler is presented and implemented at 5.8 GHz using coplanar waveguide technology. With the slot-coupled directional coupler, the proposed matrix was designed without using any crossovers as used in conventional Butler matrices, which leads to significant size reduction and loss minimization. To examine the performance of the proposed matrix, experimental prototypes of the multilayer directional coupler and the Butler matrix were fabricated and measured. Furthermore, a four-antenna array was also designed and fabricated at 5.8 GHz and then connected to the matrix to form a beamforming antenna system. As a result, four orthogonal beams at -45deg, -15deg, 15deg, and 45deg are produced. Measured results on the entire system agree well with the theoretical predictions, validating the proposed design