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.

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 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.

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 new structure of millimetre-wave focusing antennas is presented. It consists of a plane-parallel Fabry-Perot resonator comprising two uniform and non-uniform inductive metal meshes excited by a horn antenna. The beam focusing is performed with the non-uniform mirror the geometry of which is chosen so that it behaves as a spherical equiphase surface with a desired radius of curvature. The resulting radiation patterns are Gaussian; their directivity is controlled by the curvature of the synthesised wavefront. This concept is successfully validated in the 60 GHz band.

This Letter deals with millimeter microstrip/thick‐slot/microstrip transitions. This kind of transition permits multilayer microstrip antenna arrays to feed. The objectives were to develop and to optimize this transition at 60 GHz, with the use of a low‐loss, low‐cost substrate. A thick ground plane with a slot is introduced between the two substrate layers to rigidify the final structure. Then several transitions were realized and measured in the 60‐GHz band to validate the calculation. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 100–103, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10385

A dual-polarized array operating in the 250-500-MHz frequency range is analyzed and realized for RCS measurements in an anechoic chamber. The elementary dual-polarized source is presented, and then the array is completely analyzed with a parallel code solver. A comparison between computed and experimental results is given for the source impedance and radiation patterns of the array. (C) 2002 Wiley Periodicals, Inc.

Because of their simplicity, slot fed circular microstrip antennas (MA) are popular. Even more popular are MAs conformally printed on curved surfaces, such as spherical-circular MAs because of their higher degree of freedom. A very attractive candidate is a discrete Luneburg lens, which is a layered dielectric sphere. To simulate the antenna, we use the Method of Analytical Regularization (MAR), sometimes called the semi-inversion method. Generally, it converts a first-kind singular integral or series equation to a well-conditioned second-kind Fredholm matrix equation, and therefore serves as a perfect pre-conditioner of an ill-posed problem. Both numerical convergence and efficiency are achieved and matrix-truncation error is controlled.

Accuracy of equivalent circuit models of periodic grids is investigated in amplitude and phase in the visible region. The grids studied here are one-dimensional (1D) and two-dimensional (2D) inductive thin metal meshes. They are located in free space and are illuminated by a plane wave under normal incidence. The range of validity and the accuracy of conventional circuit models are defined by comparison with rigorous results obtained with the Finite-Difference Time-Domain (FDTD) method. In particular, it is shown that electrical models of 1D grids are accurate, whereas equivalent circuits of 2D grids should be used very cautiously. Then, a new formulation is proposed to overcome this major drawback. In the non-diffraction region, the agreement between our model and the FDTD results is within 2% for the power reflectivity and 1° for the phase over a very wide range of strip widths.

In this paper, the problem of radiation of a dipole antenna on the surface of partially screened layered dielectric sphere is considered. The method of analytical regularization based on the Abel integral equation technique has been applied, which reduces the problem to an infinite-matrix equation of the Fredholm second kind. Numerical results for some basic antenna characteristics are demonstrated.

Several configurations of millimeter wave Gaussian Beam Antennas (GBAs) are studied in this paper. A GBA is a quasi-planar radiating structure comprising a piano-convex half-wavelength Fabry-Perot (FP) resonator excited by a guided source or by a printed source. Both partially transparent mirrors of the resonator are formed with two-dimensional metal meshes. GBAs have very low side lobes, because of the gaussian distribution of the aperture electric field. They can be efficiently used in Wireless Local Area Networks in the 60 GHz band. After a brief presentation of intrinsic properties of FP cavities illuminated by a plane wave under normal incidence, performances of four passive GBAs are described and compared to theoretical results: the first two configurations concern cavities fed either by a waveguide (GBA#1), or by a pyramidal horn antenna (GBA#2); in the last two ones, the cavities are excited by a linearly polarized microstrip patch antenna (GBA#3), or by a coaxial-probe circularly polarized antenna array (GBA#4). These various examples enable to deduce and to compare typical radiation performances of GBAs, depending on (i) the feeding technique (planar or guided), on (ii) the geometry of the FP resonator (radius of curvature, grid parameters) and on (iii) the polarization (linear or circular). In particular, for a planar primary source, it is shown that the directivity and the efficiency of GBAs are respectively in the range [15.5 dB-23.5 dB] and [20%-50%], if power reflectivities of both mirrors are higher than 96.5% and lower than 99.5%, and if the radius of curvature of the cavity varies between 30 lambda (0) and 1600 lambda (0).

The development of wireless indoor communication in the millimeter-wave domain (60 GHz) requires antenna arrays with specific performances. Microstrip technology is attractive at these frequencies if one uses material with weak losses and a low-cost technology. Glass Teflon, alias RT/D Duroid 5880, or polymethyl-pentene, alias TPX, are good candidates. But spurious radiation due to the feeding network often occurs in the millimeter band. These effects often increase the cross-polarization component and the sidelobe level. A solution to reduce these problems is to use slot-coupled printed antenna arrays, with radiating elements that are separated from the feeding lines by the ground plane. Various types of patterns have been investigated, either directive or, on the contrary, with a large sector beam. (C) 2001 John Wiley & Sons, Inc.

A mathematically accurate method of analysis of a spherical-disk antenna conformally printed on a dielectric-covered metallic sphere is presented. The antenna is fed by a radial coaxial probe simulated by an electric dipole. The solution consists of reducing the boundary-value problem to the dual-series equations, and further to a regularized infinite-matrix equation. This procedure is based on the analytical inversion of the static part of the problem of a disk in free space, and results in a stable and fast algorithm with a guaranteed convergence. Numerical data on the basic antenna characteristics are presented. (C) 2000 John Wiley & Sons, Inc.