Halim Boutayeb

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.

Gain Enhancement of a Microstrip Patch Antenna Using a Cylindrical Electromagnetic Crystal Substrate

The performance of a circular microstrip patch antenna is improved using a new cylindrical electromagnetic bandgap (EBG) substrate. The microstrip patch antenna is fed by a coaxial probe and is integrated within a cylindrical electromagnetic bandgap substrate, based on the mushroom-like substrate, to increase the antenna gain. The cylindrical electromagnetic bandgap structure is a combination of two periodic structures with different periods. One is made of metallic rings and the other of grounding vias, which are disposed such as to form a radially and circularly periodic structure. A parametric analysis using a full-wave method was carried out in order to design the EBG structure. With the proposed concept, an antenna prototype was fabricated and tested. The radiation patterns and return loss obtained from measurements show a good impedance matching and a gain enhancement of the proposed antenna.

Hybrid Dielectric Resonator Antenna With Circular Mushroom-Like Structure for Gain Improvement

In this paper, the performance of a cylindrical dielectric resonator antenna (DRA) is improved using a new cylindrical electromagnetic bandgap substrate. The DRA is fed by a coaxial probe and integrated within a cylindrical electromagnetic bandgap (EBG) substrate to increase the antenna gain. The cylindrical electromagnetic bandgap structure is composed of two distinctive periodic structures. The first structure is made of metallic rings, while the second is formed of grounding vias, which are placed radially and circularly. To describe and optimize this EBG stucture, a parametric study using a finite integration method was carried out. Furthermore, an antenna prototype was fabricated and measured to validate the proposed concept. The radiation patterns and return loss obtained from measurements demonstrate a good performance in terms of impedance matching and gain enhancement.

Broadband Microstrip-Fed Dielectric Resonator Antenna for X-Band Applications

A new microstrip fed low profile broadband dielectric resonator antenna is proposed. The antenna is composed of a dielectric resonator, a microstrip fed stepped patch and an intermediate substrate. The stepped patch and the intermediate substrate allow to widen the matching bandwidth. Using a finite integration method (CST Microwave), a parametric investigation was performed for the optimization. To validate the proposed design, a prototype of the optimized antenna was fabricated and measured. The predicted results are compared with the measured data, and a good agreement is achieved. The proposed antenna offers a fractional bandwidth of 50% around the center frequency 10.16 GHz, and relatively stable radiation patterns in the matching band.

Noise and Sensitivity of Harmonic Radar Architecture for Remote Sensing and Detection of Vital Signs

This paper addresses noise and sensitivity issues in remote sensing and detection of vital signs based on a continuous wave biomedical radar operating at multiple harmonic carrier frequencies or channels. This Doppler radar makes use of a single mixer, taking advantage of the inherent nonlinearity and harmonic characteristics of the mixer. Other system building elements such as antennas, amplifiers, and circulators can also operate at and comply with multiple harmonic frequencies or channels requirements, which makes the system compact. Noise is one of the most important factors that affect the sensitivity of this type of system. The total noise is the combined contribution of thermal noise, residual phase noise, and flicker noise. Flicker noise is found to be the critical parameter for the baseband detection. Experimental results show that with the use of the harmonic radar technique, the flicker noise can be reduced by 20 dB around 1-Hz baseband frequency compared with the counterpart in a conventional radar operating at single frequency. The noise and sensitivity of a harmonic radar system operating at 12 and 24 GHz for vital signs detection are studied theoretically and experimentally. It is proven that the harmonic radar solution is able to increase detection sensitivity by increasing the signal-to-noise ratio. The performance of the harmonic radar is tested experimentally with a moving plate and also a real patient. For the heartbeat detection, an oximeter giving the oxygen saturation of blood and heart rate is used as the reference.

Integrated radar systems for precision monitoring of heartbeat and respiratory status

This work presents simulation and measurement results of the vital sign parameters based on low-power microwave and millimeter-wave monitoring systems through Doppler radar techniques. The cardiac beating and the breathing of patients are examined. Three systems operating at 5.8 GHz, 24 GHz and 35 GHz, respectively, are designed, simulated, and fabricated. Using such three systems and applying signal processing techniques, measured signals obtained at distance up to 1 m from the patient of reference are presented. These results show that the heartbeat and the frequency of breath are well detected which validates our radar analysis and design approach. Performances (sensitivity, complexity, etc.) of the different systems are compared and studied, showing that the highest sensitivity detection can be achieved with the system at the highest frequency (35 GHz) in this case.

Metallic Cylindrical EBG Structures With Defects: Directivity Analysis and Design Optimization

An analysis is presented of the directivity and the design optimization of cylindrical electromagnetic band gap (CEBG) structures constituted of metallic wires and with defects. The directivity is studied for different transversal periods, radial periods and numbers of rings. In the proposed configuration, the defects are designed by removing multiple wires, such as to form a horn-shaped aperture inside the periodic structure. From numerical results, obtained with a home-made finite difference time domain (FDTD) code, it is shown that the structures with defects present a directive beam in the stop-bands of the corresponding structures without defects. The radiation characteristics of the CEBG material are compared with those of an equivalent-plane sectoral horn to explain the directivity mechanism. An optimization method is also proposed for minimizing the number of wires. To validate the analysis, an optimized directive antenna with a dipole as an excitation source was fabricated and measured.

Internally Excited Fabry-PÉrot Type Cavity: Power Normalization and Directivity Evaluation

This letter presents a new approach to analyze Fabry-PÉrot cavities excited from their inside by electromagnetic waves. While Fabry-PÉrot cavity antennas found in literature use often the magnitude of the transmission coefficient to determine the antenna directivity, the proposed approach suggests a new strategy that uses a normalized transmission coefficient, which is derived by using a transmission line model and by considering the available power from the source. Furthermore, a new analytical expression is also proposed for evaluating the directivity. The obtained results are presented and compared to experimental results reported in literature.

BANDWIDTH WIDENING TECHNIQUES FOR DIRECTIVE ANTENNAS BASED ON PARTIALLY REFLECTING SURFACES

The directivity bandwidth of Fabry-Perot directive antennas is first evaluated theoretically. Then, different techniques are proposed to widen the directivity bandwidth of antennas using Partially Reflecting Surfaces. The bandwidths obtained with the proposed solutions are compared to the bandwidth of a classical Fabry- Perot directive antenna.

Analysis of radius-periodic cylindrical structures

The purpose of this communication is to present an analysis method for cylindrical structure which are periodic along their radii and are excited by a line source placed in the center. At first. we derive analytical formulas for the transmitted wave and the wave inside the structure of a single layer cylindrical structure, which allow to extract the characteristics of the cylindrical layer. Then we obtain the dispersion equation and the transmission coefficient of multiple layer periodic structures.