Mohamed Himdi

Synthesis of uniform amplitude unequally spaced antenna arrays using the differential evolution algorithm

A computationally efficient global optimization method, the differential evolution algorithm (DEA), is proposed for the synthesis of uniform amplitude arrays of two classes, i.e., unequally spaced arrays with equal phases and unequal phases. Phase-only synthesis and the synthesis of uniformly exited unequally spaced arrays (position only synthesis) are compared and it is seen that, by using the unequal spacing, the number of array elements can be significantly reduced for attaining reduced sidelobe levels. From the DEA-based synthesis of unequally spaced arrays with uniform amplitudes and unequal phases, it is found that a tradeoff exists between the size of the unequally spaced arrays and the range of phases for the same radiation characteristics. The proposed synthesis technique using uniform amplitudes, unequal spacing, and unequal phases (position-phase synthesis) not only decreases the size of the array for the same sidelobe level compared to both the phase-only synthesis and position-only synthesis but also retains their advantages.

ELECTRONICALLY SWITCHED BEAM DISK-LOADED MONOPOLE ARRAY ANTENNA

A disk-loaded monopole array antenna with coplanar waveguide (CPW) feeding systems that has the capability of beam switching has been successfully demonstrated. The antenna utilises the advantages of CPW and the transmission line of input impedance equation and is integrated with RF/Microwave devices to enable beam switching in the elevated and azimuthal planes. The measured gain of the antenna in the direction of the open-circuited parasite element is in the range of 5.10 to 5.60dBi. It has good input return loss at 2.45GHz and produces useful gain in the direction of the open circuited element. The E- and H-plane patterns show that the beam can be steered by pin diodes switching.

A sliced spherical Luneburg lens

The Luneburg lens (LL) represents a very attractive candidate for many applications such as multibeam antennas, multifrequency scanning, and spatial scanning, due to its focusing properties. Indeed, it is a dielectric sphere on which each surface point is a frequency-independent perfect focusing point. This is produced by its index governing law n, which follows the radial distribution n/sup 2/=2-r/sup 2/, where r is the normalized radial position. Practically, an LL is manufactured as a finite number of concentric homogeneous dielectric shells - this is called a discrete LL. The inaccuracies in the curved shell manufacturing process produce intershell air gaps, which degrade the performance of the lens. Furthermore, this requires different materials whose relative dielectric constant covers the range 1-2. The paper proposes a new LL manufacturing process to avoid these drawbacks. The paper describe the theoretical background and the performance of the obtained lens.

Interactions between 60-GHz millimeter waves and artificial biological membranes: dependence on radiation parameters

Due to the increasing interest in millimeter-wave (MMW) applications for wireless communication systems, the investigation of their potential biological effects is of utmost importance. In this paper, we report experimental results of the study of interactions between low-power radiation at 60 GHz and artificial models of biological membranes. In the first part of this study, we demonstrate an increase of superficial pressure of phospholipid monolayers during MMW exposure. Two of the most prominent in quantity lipid constituents of biological membranes, dipalmitoylphosphatidylcholine and dioleoylphosphatidylcholine, are considered. The role of different radiation parameters, namely, power density, polarization, amplitude modulation, permanent, and discontinuous exposure, is discussed. The results have proved to be reproducible in independent experiments. In the second part of this study, through atomic force microscopy analysis, we investigate the influence of MMW radiation on the microdomain distribution in mixed phospholipid monolayers with phase separation. No significant modifications are observed in microdomain distribution after 5 h of exposure. The main outcomes of this study lead to the conclusion that short-term low-power MMW exposures result in an increase of lateral pressure of the phospholipid monolayer, but their influence is not sufficiently strong to disturb phospholipid microdomain organization in biomembranes

Design of an unequally spaced reflectarray

We present the design and experimental results of an X-band unequally spaced reflectarray of microstrip patch elements. For a given number of elements, it is shown that reduced sidelobe levels can be attained for unequally spaced reflectarrays compared to that of equally spaced reflectarrays with no significant change in directivity and array size. The synthesis tool used for deriving the element positions is a variant of the genetic algorithm, namely the differential evolution algorithm.

Ka-Band Phased Array Antenna for High-Data-Rate SATCOM

The general issue of this letter deals with the design of a phased array antenna for high-data-rate SATCOM. A final demonstrator antenna could be installed on an unmanned aerial vehicle (UAV) to communicate with a satellite in Ka-band. First, a compact reflection-type phase shifter is designed and realized. Second, the conception of a phased array antenna prototype is detailed. Third, a new calibration method is involved that can provide the bias voltage to be applied to each phase shifter in order to scan the beam in the desired direction.

Scattering of Spherically and Hemispherically Stratified Lenses Fed by Any Real Source

An analytical method to compute the scattering of spherically and hemispherically stratified lens antennas is described. The expansion of any real source on spherical wave functions is detailed and validated by comparison to commercial software simulations and measurements at both 50 GHz and 77 GHz. A mode matching technique (MMT) based on spherical wave functions is first used to analyze the scattering by spherically stratified lens antennas. The far field patterns and directivity obtained are in excellent agreement with commercial software simulations and measurements for a six-shell Luneburg lens at 6 GHz. This MMT is then extended to hemispherically stratified lens antenna analysis. Its validation is also carried out by comparisons to both commercial software and measurements for a three-shell half Maxwell fish-eye lens fed by an open-ended waveguide at W-band. The expansion on spherical modes gives direct access to the field everywhere. To highlight the progressive focusing effect of inhomogeneous lens antennas, the electric field is mapped in terms of magnitude and phase in the neighborhood of the entire structure. One of the originalities of this work is the quantification of the reaction created by the scatterer on the feed. Narrowing the scatterer to a stratified lens does not affect the generality of the presented procedure. While providing controlled accuracy, the MMT tremendously reduces both computation time and memory load in comparison to commercial software.

Foam Based Luneburg Lens Antenna at 60 GHz

An innovative technological process is investigated to easily manufacture inhomogeneous Luneburg lenses. A unique foam material is drilled and pressed to achieve the difierent dielectric constant needed to follow the index law inside the lens. The performance of such 60GHz antenna is described and the antenna prototype is measured in terms of gain and radiation patterns. The results show a good e-ciency (60% with a directivity of 18{19dBi) and demonstrate the feasibility of this kind of Luneburg lens, through the use of a simple technological process. The lens with a diameter of 56mm and a thickness of 3mm operates in the 57{66GHz bandwidth. The magnitude of S11 parameter is under i10dB in the whole bandwidth and an half-power beamwidth of 5 - and 50 - in H-plane and E-plane respectively is reached.

An Active Reconfigurable Antenna at 60 GHz Based on Plate Inhomogeneous Lens and Feeders

The conception and performances of a 60 GHz active antenna, reconfigurable in terms of radiation pattern is described in this paper. This antenna is based on a plate inhomogeneous Luneburg lens fed by several ridged waveguide sources. The manufacturing technique of the plate lens is briefly described and its measured radiation patterns are given, showing the good performances of this lens. Simulated and measured radiation patterns are given for a passive lens antenna fed by several sources. The results show the beam scanning capability of this antenna. The active antenna is described and measurements of radiation patterns for several beams are given and demonstrate the beam scanning and beam shaping reconfigurability.

Performance and Radiation Patterns of a Reconfigurable Plasma Corner-Reflector Antenna

A novel reconfigurable plasma corner reflector antenna is proposed to better collimate the energy in forward direction operating at 2.4 GHz. Implementation of a low-cost plasma element permits beam shape to be changed electrically. The maximum measured gains are 5.7, 10.8, and 10.5 dBi for the omnidirectional, single-, and double-beam shapes, respectively.