Gaël Godi

Performance of reduced size substrate lens antennas for Millimeter-wave communications

This paper presents the theoretical performance (input impedance, -10 dB return-loss bandwidth, radiation patterns and surface efficiencies) of reduced size substrate lenses fed by aperture-coupled microstrip patch antennas. The diameter of the extended hemispherical homogeneous dielectric (/spl epsiv//sub r,lens/) lenses varies between one and five wavelengths in free-space, in order to obtain radiating structures whose directivity is comprised between 10 and 25 dB. A lot of configurations of lenses are investigated using the finite-difference time-domain methods technique and compared in the 47-50 GHz band as a function of their diameter, extension length and dielectric constant. In particular, the analysis of internal reflections-in time and frequency domains-shows that the latter have potentially a strong influence on the input impedance of small lens antennas, even for low values of /spl epsiv//sub r,lens/(2.2), whereas the usual limit (beyond which anti-reflection coatings are required) is /spl epsiv//sub r,lens/=4. We also demonstrate that the diffraction limit of reduced size lenses is reached for extension lengths varying between 50% and 175% of the extension of synthesized ellipses, depending on the lens material and diameter. Finally, we show that superdirective structures with surface efficiencies reaching 250% can be obtained with small lens diameters, justifying the interest in reduced size lens antennas.

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.

Small Hemielliptic Dielectric Lens Antenna Analysis in 2-D: Boundary Integral Equations Versus Geometrical and Physical Optics

We assess the accuracy and relevance of the numerical algorithms based on the principles of geometrical optics (GO) and physical optics (PO) in the analysis of reduced-size homogeneous dielectric lenses prone to behave as open resonators. As a benchmark solution, we use the Muller boundary integral equations (MBIEs) discretized with trigonometric Galerkin scheme that has guaranteed and fast convergence as well as controllable accuracy. The lens cross-section is chosen typical for practical applications, namely an extended hemiellipse whose eccentricity satisfies the GO focusing condition. The analysis concerns homogeneous lenses made of rexolite, fused quartz, and silicon with the size varying between 3 and 20 wavelengths in free space. We consider the 2D case with both - and -polarized plane waves under normal and oblique incidence, and compare characteristics of the near fields.

A shaping technique of substrate lens antennas with genetic algorithm

A powerful optimization procedure of substrate lens antennas has been proposed at millimeter wave frequencies. Compared to previous works, this approach is global and thus does not require the a priori knowledge of an initial lens profile computed with conventional GO-based synthesis techniques. Our design methodology combines a genetic algorithm with an efficient asymptotic analysis of the radiation characteristics of 3D substrate lens antennas.

Small hemielliptic dielectric lens antenna analysis boundary integral equations vs. GO and PO

The purpose of research is to outline the domain of applicability of the geometrical optics (GO) and physical optics (PO) in the small dielectric lens analysis. As a benchmark solution, we use the Mullers boundary integral equations (IE) discretized with trigonometric Galerkin scheme that has guaranteed and fast convergence. The lens cross-section is chosen typical for practical applications, namely an extended hemiellipse whose eccentricity satisfies the GO focusing condition. The lens flat side dimension varies between 2 and 8 wavelengths in free space, and its material is rexolite (s = 2.53). We consider the 2D case with an E-polarized plane wave incidence and extract comparison characteristics from the near field analysis.

FDTD analysis of reduced size substrate lens antennas

The input impedance and far-field radiation patterns of reduced size extended hemispherical lenses (fed by aperture-coupled microstrip patch antennas) have been investigated in the 47-50 GHz band, using the finite-difference time-domain (FDTD) technique. Good focusing capabilities and very interesting surface efficiencies have been found for some electrically small lenses. The effects of internal reflections have been quantified both in time and frequency domains. Diffraction and possible resonance effects have also been taken into account for an accurate analysis of radiating structures whose size is comparable to the operating wavelength.

Shape optimization of lens antennas for Short Range and Long Range sensors at millimeter waves

We have shown that a single antenna array excited by two different feed networks and illuminating a shaped substrate lens enables one to generate two radio coverage by properly shaping the lens profile and optimizing the array parameters (number of elements, amplitude of excitation, inter-element spacing). This concept has been successfully applied to SRR / LRR sensors. Antenna prototypes are under fabrication.

Single- and double-shell shaped lens antennas with asymmetrical radiation characteristics

A computer-aided design (CAD) tool is proposed for the analysis and optimization of multi-shell Integrated Lens Antennas (ILAs) of arbitrary three-dimensional (3-D) shape and dielectric constitution. The analysis of the lens performance is carried out using the conventional hybrid geometrical / physical optics (GO/PO) method. The optimization of the lens shape is based on a binary genetic algorithm (GA) coupled to the GO/PO kernel. The ILAs considered here are single- and double-shell lenses of arbitrary shape. Two designs of single-shell lenses made in Rexolite and ceramic materials are presented and compared for non axis-symmetric Gaussian far-field specifications. The drawbacks of single-shell geometries are highlighted, and a double-shell ILA is designed in order to maximize the power transfer efficiency of the antenna. These results demonstrate that double-shell configurations can improve significantly the performance of ILAs of moderate size.

Far field millimetric band antenna test facility : Positioning procedure using phase measurements

Since several years IETR has been conducting active research activities on the modelling and design of millimetric radiating structures and devices. The experimental validation of innovative designs and homemade electromagnetic CAD tools is of uppermost importance. To this end, prototyping capabilities and complementary sets of antenna test facilities at millimetre waves are available for routine experiments (e.g. [18-110] GHz far field chamber, [2-110]GHz coaxial vector network analyser). In such a context, antenna measurements are considered as a key step of the research process. Even though our measurements facilities are not used for certification purposes, they need to provide reproducible, reliable and accurate data for a wide diversity of antenna topologies and dimensions. Then, the definition of the same coordinates system for measurements and simulations remains a sensitive point. We present in this paper an easy-to-use positioning procedure based on phase measurements from Ka-band to W-band. This technique is briefly described in Section 1. Various experimental results are given in Section 2 and conclusion are drawn in section 3..