Anthony Rolland

Test of the FDTD accuracy in the analysis of the scattering resonances associated with high-Q whispering-gallery modes of a circular cylinder

Our objective is the assessment of the accuracy of a conventional finite-difference time-domain (FDTD) code in the computation of the near- and far-field scattering characteristics of a circular dielectric cylinder. We excite the cylinder with an electric or magnetic line current and demonstrate the failure of the two-dimensional FDTD algorithm to accurately characterize the emission rate and the field patterns near high-Q whispering-gallery-mode resonances. This is proven by comparison with the exact series solutions. The computational errors in the emission rate are then studied at the resonances still detectable with FDTD, i.e., having Q-factors up to 10(3).

Assessment of FDTD Accuracy in the Compact Hemielliptic Dielectric Lens Antenna Analysis

We assess the accuracy of a standard finite-difference time-domain (FDTD) code in the analysis of the near and far-field characteristics of two-dimensional (2-D) models of small-size dielectric lens antennas made of low or high-index materials and fed by the line sources. We consider extended hemielliptic lenses and use the Muller boundary integral equations (MBIE) method as a suitable reference solution. Inaccuracies of FDTD near so-called half-bowtie resonances are detected. Denser meshing reduces the error of FDTD only to a certain level determined by the type of absorbing boundary conditions used and other fine details of the code. Out of these resonances, FDTD code is demonstrated as capable of providing sufficient accuracy in the near and far-field analysis of small-size hemielliptic lenses typical for the millimeter-wave (mm- wave) applications.

Optimization of Reduced-Size Smooth-Walled Conical Horns Using BoR-FDTD and Genetic Algorithm

An accurate optimization tool has been developed to design arbitrarily-shaped axis-symmetrical devices. It is based on the combination between a genetic algorithm (GA) and a finite-difference time-domain (FDTD) solver formulated in a cylindrical coordinate system. For validation purposes, this tool is applied to design several smooth-walled compact conical horns with a large flare angle (90°) in the 60-GHz band. The unavoidable phase distortions appearing in the horn aperture are compensated by loading the horn mouth with thin shaped dielectric lenses made in Rexolite. Based on these test cases, several synthesis strategies are discussed and compared in order to select the best antenna prototype among those synthesized. A scaled version of this prototype has been fabricated to operate around 29.5 GHz. The numerical and experimental results are in excellent agreement. Horn size reduction rates up to 80% have been reached.

Size and Weight Reduction of Integrated Lens Antennas Using a Cylindrical Air Cavity

A simple and low-cost solution to reduce the height and weight of extended hemispherical lenses is proposed based on the introduction of a cylindrical air cavity above the primary feed. The presence of an additional air-dielectric interface enables one to shorten the focal length of the lens, which leads to antenna height and weight reductions of 13% and 27%, respectively. The communication describes the design principle and performance characteristics of the reduced-size integrated lens antenna, superimposed with a conventional synthesized elliptical one. Both prototypes are fabricated in Rexolite and measured in Ka band. A good agreement between the performance characteristics of the antennas is observed. The additional advantages of the proposed approach are explained, and its applicability for lens antennas made of high-k materials is discussed.

Flat-Shaped Dielectric Lens Antenna for 60-GHz Applications

We describe the performance of a flat shaped dielectric lens antenna designed to produce a flat-top beam in H-plane and a nearly omni-directional pattern in E-plane in the 60-GHz band. Such radiation characteristics may be useful for access points or user terminals in high data rate wireless local area networks. For the antenna design, a specific two-stage methodology combining 2-D and 3-D modeling has been implemented. First, the lens shape is optimized in 2-D using a 2-D FDTD kernel coupled to a genetic algorithm. Second, all building blocks of the final antenna (3-D lens with a finite thickness, antenna feed) are optimized using the solution of the 2-D problem as an initial guess. This strategy has been validated experimentally: a 2.5-mm-thick flat lens in Rexolite with a shaped profile in H-plane has been fabricated and measured. It is shielded by two 1-mm-thick half metallic disks. The radiation patterns are very stable from 57 to 63 GHz, and the total antenna efficiency is better than 50%.

Axisymmetric Resonant Lens Antenna With Improved Directivity in Ka-Band

A compact-size shaped dielectric lens antenna (DLA) is designed and optimized in Kα-band (29.5 GHz) using a new synthesis tool based on the combination of a genetic algorithm and BoR-FDTD solver. The antenna is fabricated in Rexolite and fed by a circular waveguide with a flange and an optimized integrated dielectric taper. As demonstrated, the proposed antenna combines features intrinsic to lens, resonant, and reflector antennas. The attractive performance of the antenna (in terms of directivity and sidelobe level) is demonstrated numerically and experimentally by comparison to a conventional extended hemispherical DLA.

Shaped Lens-Like Dome for UWB Antennas With a Gaussian-Like Radiation Pattern

A multi-shell lens-like dome antenna (LLDA) with an axis-symmetrical Gaussian-like radiation pattern is presented. The dome profile is optimized using in-house software based on the genetic algorithm and Geometrical Optics/Physical Optics technique. Stable radiation characteristics are achieved within the entire V-band (50–75 GHz), thanks to the optimized shape and also the introduction of two matching layers inside and outside of the dome. The dome core and matching layers of the LLDA are fabricated in Rexolite and foam, respectively. A good agreement between the measured and simulated data is obtained. The capability of a multi-shell dome antenna to produce a low-dispersive gain and Gaussian-like radiation pattern is illustrated.

Smooth-Walled Light-Weight Ka-Band Shaped Horn Antennas in Metallized Foam

Several smooth-walled axis-symmetrical dielectric-loaded horn antennas with large flare angles have been designed and characterized in Ka-band. They have been optimized using an in-house CAD tool based on the BoR-FDTD technique and genetic algorithms. Two antenna configurations have been compared: in the first case, only the metallic profile of the horn is shaped and the radiating aperture remains flat, whereas in the second one, the shapes of the horn profile and the aperture are simultaneously optimized. The impact of both techniques in terms of antenna size and performance is discussed. An original fabrication process (metallized foam) has been developed to produce monolithic prototypes. Two prototypes with optimized shapes have been fabricated, and their main characteristics (radiation characteristics, bandwidth, compactness, weight) are compared to those of a standard conical horn used as a reference (same flare angle, same diameter, but without shaped profile). Our results show that the proposed design and fabrication procedures enable us to produce reduced-size horns with high radiation efficiency; the total loss, including the transition loss, is lower than 1 dB in average around 29.5 GHz.

Lens-Corrected Axis-Symmetrical Shaped Horn Antenna in Metallized Foam With Improved Bandwidth

A lens-corrected smooth-walled axis-symmetrical dielectric-loaded horn antenna is designed and characterized in Ka-band using the bodies of revolution finite-difference time domain (BoR-FDTD) technique and genetic algorithm. The joint optimization of the horn and dielectric loading profiles enables us to develop a horn with a very good gain performance achieved in a frequency range of about 18%. Compared to earlier results, the bandwidth improvement exceeds a factor two. A lightweight prototype is fabricated in metallized foam. A very good agreement between the numerical and measured data is obtained.

Hexagonal-Shaped Broadband Compact Scrimp Horn Antenna for Operation in

The performance of compact linearly polarized Short Circular Ring-loaded horn with Minimized cross-Polarization (Scrimp) horns with different aperture sizes is first evaluated using an in-house finite-difference time-domain (FDTD) computer-aided design (CAD) tool. Then, a very short hexagonal Scrimp horn with an aperture size of 1.5λ0 is designed in C -band; its height is only 1.26λ0 . The experimental results demonstrate that the aperture efficiency is higher than 80% with a reflection coefficient lower than -17 dB over a 12.6% frequency bandwidth. Radiation patterns of excellent quality are measured with a cross-polarization level lower than - 28 dB over the entire bandwidth. These antennas are very attractive candidates for high-power focal array configurations in multifeed systems.