Jean-Pierre Daniel

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.

Tunable bilayered metasurface for frequency reconfigurable directive emissions

The directive emission from a bilayered metamaterial surface is numerically and experimentally reported. The LC-resonant metasurface is composed of both a capacitive and an inductive grid constituted by copper strips printed on both sides of a dielectric board. By the incorporation of varactor diodes in the capacitive grid, resonance frequency and phase characteristics of the metamaterial can be tuned. The tunable phase metasurface is used as a partially reflecting surface in a Fabry–Perot resonance cavity. Far field radiation patterns obtained by direct measurements show the reconfigurability of emission frequency while maintaining an enhanced directivity.

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.

Mutual coupling between antennas--Optimization of transistor parameters in active antenna design

It is demonstrated theoretically that mutual coupling effects on the radiation pattern of an element in the presence of another one can be reduced with appropriate loads. Constant coupling circles are calculated and plotted on a Smith chart. The choice of transistors for active antenna design then becomes clearer either for reception or for emission.

Study of Fabry-Perot Cavities with Metal Mesh Mirrors Using Equivalent Circuit Models. Comparison with Experimental Results in the 60 GHz Band

The equivalent circuit modelling technique is used to study the resonant frequency and Q factor of plane parallel Fabry-Perot cavities with square aperture metal mesh mirrors. Comparison of different models found in literature with experimental data in the 60 GHz band is given for thin and thick cavities. Chens model is shown to give a good agreement with measurements, as long as the cavity is not too selective and for large enough cavity.

MAR analysis of a spherical-circular printed antenna with finite ground excited by an axially symmetric probe

The paper deals with an accurate mathematical and numerical analysis of a spherical-circular antenna printed over a coaxial spherical-circular ground conductor. A coaxial probe simulated by a radial driving current placed between two conductors excites the antenna. Consideration is done in terms of the spherical vector wave function expansions of the field in each partial domain. The problem is cast into a coupled set of the dual-series equations for the expansion coefficients, and then to an infinite-matrix equation having favorable features. This is achieved by following the Method of Analytical Regularization developed earlier for the analysis of spherical reflectors.

Theoretical Reflection Coefficient of Metal Grid Reflectors at a Dielectric Interface

Reflection properties of square apertures metal mesh mirrors are studied theoretically with the Finite-Difference Time-Domain (FDTD) method associated to Floquet Boundary Conditions. The reflector is illuminated by a normally incident plane wave and is located at an interface between two semi infinite low loss dielectric materials. Reflectivity and phase of the reflection coefficient are given in the non diffraction region for a wide range of square apertures, and for the four situations corresponding to an interface between free space and fused quartz.

Reduction of mutual coupling between active monopoles: Application to superdirective receiving arrays

Theoretical results and measurements of mutual coupling between active monopoles show that the incorporation of a field-effect transistor (FET) with a shunt input inductance leads to large reduction of interactions at reception. Each active monopole then works as an isolated element, and feed requirements of active array become easier to obtain. Realization of a superdirective array with an appreciable bandwidth confirms the main possibilities of active antennas.

Revisiting the waves on a coated cylinder by using surface-impedance model

The results of analytical and numerical study of the modes propagating on an impedance-surface circular cylinder are communicated. Besides the well-known axially symmetric Sommerfelds mode, another hybrid mode, having a single azimuthal variation, can propagate at any frequency. For a realistic cylindrical conformal antenna, the both wavenumbers are quite comparable. This may cause additional coupling between array antenna elements.

Discrete Luneburg lens fed by a spherical-circular printed antenna in axisymmetrical mode - accurate analysis by MAR

Research has been carried out on circular microstrip antennas (MA) fed by a probe located at the center to ensure an omnidirectional pattern. Even more attractive are MAs conformally printed on curved surfaces, such as spherical-circular MA (SCMA). Many new applications need sophisticated antennas, which possess a number of special properties. Indeed, data transmissions via low Earth orbit satellites or military tracking X-band radar constrain one to have an agile scanning beam. A very attractive candidate for all these applications is the Luneburg lens (LL). Practically, LL is manufactured as a finite number of concentric homogeneous dielectric shells