Laurent Le Coq

A new accurate design method for millimeter-wave homogeneous dielectric substrate lens antennas of arbitrary shape

The synthesis and the optimization of three-dimensional (3-D) lens antennas, consisting of homogeneous dielectric lenses of arbitrary shape and fed by printed sources, are studied theoretically and experimentally at millimeter(mm)-wave frequencies. The aim of the synthesis procedure is to find a lens profile that transforms the radiation pattern of the primary feed into a desired amplitude shaped output pattern. This synthesis problem has been previously applied for dielectric lenses and reflectors. As far as we know, we propose, for the first time, to adapt and implement it for the design of substrate lens antennas. The inverse scattering problem is solved in two steps. In the first one, the geometry of the 3-D lens is rigorously derived using geometrical optics (GO) principles. The resulting second-order partial-differential equation is strongly nonlinear and is of the Monge-Ampe/spl grave/re (M.A) type. The iterative algorithm implemented to solve it is described in detail. Then, a surface optimization of the lens profile combined with an analysis kernel based on physical optics (PO) is performed in order to comply with the prescribed pattern. Our algorithms are successfully validated with the design of a lens antenna radiating an asymmetric Gaussian pattern at 58.5 GHz whose half-power beamwidth equals 10/spl deg/ in H plane and 30/spl deg/ in E plane. The lens is illuminated by a microstrip 2/spl times/2 patch antenna array. Two lens prototypes have been manufactured in Teflon. Before optimization, the measured radiation patterns are in very good agreement with the predicted ones; nevertheless, the -12 dB side lobes and oscillations appearing in the main lobe evidence a strong difference between the desired and measured patterns. This discrepancy is significantly reduced using the optimized lens.

Multi-Beam Multi-Layer Leaky-Wave SIW Pillbox Antenna for Millimeter-Wave Applications

This work proposes a novel multi-beam leaky-wave pillbox antenna. The antenna system is based on three main parts: feeding part (integrated horns), quasi-optical system and radiating part. The radiating and input parts are placed in two different stacked substrates connected by an optimized quasi-optical system. In contrast to conventional pillbox antennas, the quasi-optical system is made by a pin-made integrated parabola and several coupling slots whose sizes and positions are used to efficiently transfer the energy coming from the input part to the radiating part. The latter consists of a printed leaky-wave antenna, namely an array of slots etched on the uppermost metal layer. Seven pin-made integrated horns are placed in the focal plane of the integrated parabola to radiate seven beams in the far field. Each part of the antenna structure can be optimized independently, thus facilitating and speeding up the complete antenna design. The antenna concept has been validated by measurements (around 24 GHz) showing a scanning capability over ±30° in azimuth and more than 20° in elevation thanks to the frequency scanning behavior of the leaky-wave radiating part. The proposed antenna is well suited to low-cost printed circuit board fabrication process, and its low profile and compactness make it a very promising solution for applications in the millimeter-wave range.

Compact Ka-Band Lens Antennas for LEO Satellites

Two new compact lens antenna configurations are presented and compared for data link communications with LEO satellites at 26 GHz. These lenses match a secant type radiation pattern template in the elevation plane while having a mechanically scanned sector beam in azimuth to enhance gain as much as possible. No rotary joints or multiple feeds are required and emphasis is put also on the compactness of the proposed solutions (< 6lambda0). Two alternative lens configurations are evaluated numerically and experimentally: one is based on modified axial-symmetric dome lens geometry, and the other one consists of a full 3-D double-shell lens antenna. In contrast to current nearly omnidirectional antennas, the directivity of our lens prototypes is above 15.4 dBi. Up to 4.2 dB loss obtained in the prototypes can be significantly reduced by using lower loss dielectrics and matching layers, without affecting the conclusions. The numerical and experimental results are in good agreement with the radiation specifications given the compact size of the antennas.

Wearable Endfire Textile Antenna for On-Body Communications at 60 GHz

A textile endfire antenna operating in the 60-GHz band is proposed for wireless body area networks (BANs). The permittivity of the textile substrate has been accurately characterized, and the Yagi-Uda antenna has been fabricated using an ad hoc manufacturing process. Its performance in terms of reflection coefficient, radiation pattern, gain, and efficiency has been studied in free space and on a tissue-equivalent phantom representing the human body. It is shown that the antenna is matched in the 57-64-GHz band. Its measured on-body efficiency and maximum gain equal 48.0% and 11.9 dBi, respectively. To our best knowledge, this is the first textile antenna for on-body wireless communications reported at millimeter waves.

Characterization of the Interactions Between a 60-GHz Antenna and the Human Body in an Off-Body Scenario

Interactions between a 60-GHz microstrip patch antenna array designed for off-body communications and the human body are investigated numerically and experimentally. First, the array is characterized in free space and on a homogeneous skin-equivalent phantom in terms of reflection coefficient, radiation pattern, and antenna efficiency. Second, a multiphysics dosimetry technique is proposed and implemented to determine the specific absorption rate (SAR) and incident power density (IPD) from the heating dynamics measured on an experimental phantom using a high-resolution infrared (IR) camera. The SAR and IPD are found by fitting the analytical solution of the bio-heat transfer equation to the measured heating dynamics. The experimental and numerical results are in a very good agreement. They demonstrate that for the considered scenario the impact of the body on the antenna characteristics is almost negligible, and even relatively high radiated powers (up to 550 mW) result in exposure levels that are below international exposure limits.

Design and Characterization of 60-GHz Integrated Lens Antennas Fabricated Through Ceramic Stereolithography

Three integrated lens antennas made in Alumina and built through ceramic stereolithography are designed, fabricated and characterized experimentally in the 60-GHz band. Linear corrugations are integrated on the lens surface to reduce the effects of multiple internal reflections and improve the antenna performance. The lenses are excited by Alumina-filled WR-15 waveguides with an optimized dielectric impedance matching taper in E-plane. The main characteristics of the first two prototypes with corrugations of variable size are compared to those of a smooth lens without corrugation (third prototype). Experimentally their reflection coefficient is smaller than -10 dB between 55 GHz and 65 GHz, and their radiation characteristics (main beam, side lobe level, cross-polarization level) are very stable versus frequency. In particular, at the center frequency (60 GHz), the total antenna loss (including feed loss) is smaller than 0.9 dB and the radiation efficiency exceeds 80%.

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

60-GHz Textile Antenna Array for Body-Centric Communications

To demonstrate that commercial textiles can be used as antenna substrates at millimeter waves, a microstrip patch antenna array printed on textile is proposed for off-body communications in the 60-GHz band. The textile substrate is characterized in V-band using the open stub technique. A new fabrication process is introduced for the reliable and accurate manufacturing of millimeter-wave microstrip antennas on textiles. The antenna reflection coefficient, radiation patterns and efficiency are studied in free space, with and without bending, and on a homogeneous skin-equivalent phantom. The numerical and experimental results are in a good agreement. To the best of our knowledge, this is the first textile millimeter-wave antenna optimized for off-body communications presented in the literature at millimeter waves.

On the Near-Field Shaping and Focusing Capability of a Radial Line Slot Array

We describe the design of a radial line slot array antenna with a shaped and focused near field. The antenna is designed in such a way to control the side lobe level and beamwidth of the normal component of the electric field with respect to the radiating aperture. The design procedure consists of two steps. In the first step, the requirements on the near-field pattern are provided over a focusing plane at a given distance from the radiating aperture. A set theoretic approach is then used to derive the aperture field distribution fitting the requirements over the near field. In the second step, the aperture field distribution is synthesized by accurately placing and sizing the slots of the antenna. The spillover efficiency is maximized during the design process. The antenna is centrally fed by a simple coaxial probe. The antenna design is validated by a prototype and measurements at 12.5 GHz.

SIW Slotted Waveguide Array With Pillbox Transition for Mechanical Beam Scanning

A dual-layer pillbox antenna is proposed for mechanical beam-scanning applications at millimeter-wave frequencies. It consists of three main subsystems (multislot quasi-optical transition, input part, and radiating part). The input and radiating parts are placed in two different layers, and the quasi-optical transition behaves as a 180° E-plane coupler-type bent. The latter is made of an integrated parabolic reflector and several coupling slots etched in the metal layer located between the two substrates hosting the input and radiating parts. A physical optics analysis of the transition is proposed and compared to full-wave simulations. The radiating part is a planar slotted waveguide array. The input part is an H-plane integrated sectoral horn placed in the focal plane of the parabola and moved along a straight line to obtain the beam scanning. For the horn aligned with the parabola axis, the radiation patterns present half-power beamwidth equal to 6° and 15° in E- and H-plane, respectively. The scan range is ±35°. This mechanical scanning approach represents an attractive solution for those applications where a continuous steering of the main beam is required.