Philippe Coquet

A new concept of focusing antennas using plane-parallel Fabry-Perot cavities with nonuniform mirrors

An original configuration of low-profile directive antennas is presented in V-band. The focusing effect is performed by a plane-parallel Fabry-Perot (FP) resonator illuminated by a printed antenna. Both reflecting mirrors are made of metal strip gratings. The dimensions of the strips and slots of the nonperiodic output mirror are much smaller than the working wavelength; they are computed locally so that this mirror behaves as a spherical equiphase surface. Theoretical and experimental results show that the radiation patterns are symmetric and have low sidelobes. The antenna directivity is controlled by the value of the synthesized radius of curvature, that is to say by the nonperiodic distribution of the metal strips. It typically varies between 15 and 23.5 dB at 60 GHz. This new radiating structure is much more compact than substrate lenses and is compatible with low-cost multilayer technologies at millimeter wave frequencies. This is a possible candidate for user mobile-stations of indoor broadband communication systems.

A Millimeter-Wave Microstrip Antenna Array on Ultra-Flexible Micromachined Polydimethylsiloxane (PDMS) Polymer

The use of polydimethylsiloxane (PDMS), an ultra flexible polymer, as a substrate for the realization of reconfigurable microwave devices in the 60-GHz band is presented. As bulk PDMS is demonstrated to be lossy at millimeter waves, membrane-supported devices are considered. A new reliable and robust technological process has been developed to micromachine membrane-supported transmission lines and microstrip antenna arrays. It is shown that transmission lines printed on 20-¿m-thick membranes exhibit similar performances as bulk substrates commonly used at millimeter-wave frequencies. A microstrip antenna array has been also designed and fabricated to demonstrate the feasibility of directive antennas supported by large membranes. Promising applications for mechanical beam-steering, beam-forming, and frequency-tunable antennas are expected.

Radiation characteristics and performance of millimeter-wave horn-fed Gaussian beam antennas

Radiation characteristics and performance of Gaussian beam antennas (GBAs) are studied theoretically and experimentally in the 60 GHz band. A GBA consists of a plano-convex half-wavelength Fabry-Perot (FP) resonator excited by a guided source with a metal flange. Two reflecting metal mesh mirrors are formed on both faces of the cavity. After a review of the principles and quasi-optical performance of plano-convex FP resonators illuminated by a plane wave, a new formulation is proposed to compute the radiation patterns of GBAs: the usual expression of the waist radius inside open resonators is modified to account for the horn aperture and for the grid parameters of the plane mirror. Standard closed-form relations of vector Gaussian beams are then used to compute the radiated copolar components. In particular, it is shown that the plane mirror is not an equiphase surface, due to the metal flange of the horn. The true phase distribution is approximated by a spherical wavefront. As a result, the directivity of the antenna becomes lower than its quasi-optical value. Experimental data obtained at 60 GHz with several pyramidal horns and various cavities agree very well with the theory. Sidelobes are lower than -25 dB, and the cross-polarization level is the same as that of the primary radiator. Universal curves showing the variations of resonant frequency, -3 dB bandwidth, gain, and radiation efficiency as a function of mirror reflectivity are very useful for the design of GBAs.

VECTOR AND PARALLEL IMPLEMENTATIONS FOR THE FDTD ANALYSIS OF MILLIMETER WAVE PLANAR ANTENNAS

The 3D Finite-Difference Time-Domain (FDTD) method is a powerful numerical technique for directly solving Maxwells equations. This paper describes its implementation on high speed computers. This technique is used here for the analysis of millimeter wave planar antennas. In our algorithm, Berengers Perfectly Matched Layers (PML) are implemented as absorbing boundary conditions to mimic free space. Dielectric and metallic losses are taken into account in a recursive and dispersive formulation. We present the main techniques implemented to optimize the non-sequential program on vector computers. Besides, two parallel supercomputers of different architectures as well as a multi-user network of Sun workstations are used to investigate the parallel FDTD code. The performances obtained on vector/distributed memory massively parallel/hybrid computers show that the FDTD algorithm is ideally suited for the implementations on both vector and parallel computers. Comparisons with experimental results in the millimeter wave frequency band validate our codes.

A Millimeter-Wave Inflatable Frequency-Agile Elastomeric Antenna

This letter reports a millimeter-wave frequency-agile microstrip antenna printed on an ultrasoft elastomeric polydimethylsiloxane (PDMS) substrate. The microstrip patch antenna is supported by a PDMS membrane suspended over an air cavity. The distance H between the patch and the ground plane, and thus the resonant frequency of the antenna, are tuned using pneumatic actuation, taking advantage of the extreme softness of the PDMS membrane. A continuous frequency shift varying from 55.35 to 51 GHz (≈8%) has been obtained for a tuning range of H between 200 and 575 μm. In all configurations, the antenna remains matched and its radiation characteristics are very satisfactory.

A millimeter-wave frequency tunable microstrip antenna on ultraflexible PDMS substrate

At millimeter waves, reconfigurable antennas are increasingly needed for high-speed wireless communications and high-resolution sensing systems [1]. Recently there has been a growing interest for frequency agile antennas due to the multiplication of wireless standards in close proximity to each other. Microstrip patch antennas are widely used because they are low-cost, light-weight, low-profile and compatible with MMIC technology. Various approaches have been implemented to tune the resonance frequency of printed antennas; they are based on electrical or mechanical reconfiguration means. In the early eighties, Lee et al. [2] proposed a manually-reconfigurable circular microstrip antenna with an air gap. In [3], an electrostatically-actuated micromachined copper ground plane was used to tune a microstrip antenna from 16.8 to 17.82 GHz and in [4] electrostatic actuation was implemented to move a microstrip patch antenna fabricated on a flexible Kapton substrate to achieve a tunability between 16.91 and 16.64 GHz. One of the key issues for elaborating mechanically reconfigurable antennas at mm-waves consists in finding materials with suitable electromagnetic and mechanical properties. In this work, we use Polydimethylsiloxane (PDMS) as an antenna substrate. PDMS is an extremely flexible polymer with very low Youngs modulus (EYoung=2 MPa) and is compatible with a number of silicon micromachining techniques. PDMS exhibits many attractive features: it is low-cost, light-weight, biocompatible and chemically resistant. The feasibility and performance of PDMS-based millimeter-wave transmission lines and microstrip antenna arrays have been demonstrated in [5]-[7]. In this paper we describe a PDMS-membrane-based frequency-tunable microstrip antenna in the 60-GHz band where a pneumatic actuation is used to reconfigure the PDMS membrane over an air-filled cavity of variable height.

1 to 220 GHz Complex Permittivity Behavior of Flexible Polydimethylsiloxane Substrate

Coplanar transmission lines (CPW) are realized on polydimethylsiloxane (PDMS) substrate in order to characterize its complex permittivity, from 1 to 220 GHz. By varying the complex permittivity, the propagation constant of the PDMS-CPW calculated with full wave software is matched to those extracted by de-embedding techniques using S-parameters measurements. The real permittivity evolves from 2.9 to 2.55 while the loss tangent increases slowly to reach 0.048 at 210 GHz.

Measurement of the Thermal Conductivity of Polydimethylsiloxane Polymer Using the Three Omega Method

Polydimethylsiloxane (PDMS) has widely appeared in different electronic and medical applications. The knowledge of the thermal properties of PDMS and especially its thermal conductivity is required while processing PDMS to design a particular device. In this paper measurement of the thermal conductivity of PDMS using the three omega method is presented at different temperatures. The three omega method has been chosen because of its ease of use and accuracy. It requires the fabrication of metallic lines which act as heaters and thermometers on the surface of the material under test. A different procedure is introduced in this paper through which the metallic lines are embedded in the surface of PDMS. Experimental results are then compared to Cahills approximate solution and to the results obtained by numerical simulations using a finite element method.

An EWOD driven millimeter-wave phase shifter using a movable ultrasoft metalized PDMS ground plane

This paper reports a novel millimeter-wave microstrip phase shifter on quartz substrate with a key feature: the use of a reconfigurable ground plane supported by a metalized ultrasoft PDMS (Polydimethylsiloxane) membrane, associated to an EWOD (ElectroWetting On Dielectric) vertical actuator.

Droplet based lab-on-chip microfluidic Microsystems integrated nanostructured surfaces for high sensitive mass spectrometry analysis

We present in this paper a microsystem coupling electrowetting on digital microfluidic and nanostructured surfaces for matrix-free Laser Desorption/Ionization Mass Spectrometry (LDI-MS) analysis of small biomolecules. Silicon nanowires are processed to form highly sensitive pads for LDI analysis and also to produce superhydrophobic surfaces for enhanced transfer of droplets containing the analytes to the analyzing pads. By this way, analysis of low molecular weight compounds with high sensitivity can be achieved. In addition, wetting properties of carbon nanotubes surfaces are investigated in the perspective of further increasing the detection performances.