Ngoc Tinh Nguyen

Design and Characterization of 60-GHz Integrated Lens Antennas Fabricated Through Ceramic Stereolithography

Three integrated lens antennas made in Alumina and built through ceramic stereolithography are designed, fabricated and characterized experimentally in the 60-GHz band. Linear corrugations are integrated on the lens surface to reduce the effects of multiple internal reflections and improve the antenna performance. The lenses are excited by Alumina-filled WR-15 waveguides with an optimized dielectric impedance matching taper in E-plane. The main characteristics of the first two prototypes with corrugations of variable size are compared to those of a smooth lens without corrugation (third prototype). Experimentally their reflection coefficient is smaller than -10 dB between 55 GHz and 65 GHz, and their radiation characteristics (main beam, side lobe level, cross-polarization level) are very stable versus frequency. In particular, at the center frequency (60 GHz), the total antenna loss (including feed loss) is smaller than 0.9 dB and the radiation efficiency exceeds 80%.

Very Broadband Extended Hemispherical Lenses: Role of Matching Layers for Bandwidth Enlargement

The design and optimization of very broadband integrated lens antennas (ILAs) constitutes one of the future trends in lens antenna field. To this end we investigate numerically the radiation performance of millimeter wave ILAs coated with multiple anti reflection layers. We propose lens structures of moderate size (four wavelengths in diameter at the center frequency) and made from a dense dielectric material (ceramic). They are illuminated by two kinds of on-axis primary sources, namely a dielectric-loaded metallic waveguide and a patch antenna. This enables to assess the role of the lens illumination law on the performance of broadband ILAs. In particular, we demonstrate that ILAs coated with three stacked quarter wavelength matching layers exhibit a very broadband promising features. First their radiation characteristics remain very stable over a large frequency band: a 36% relative bandwidth is achieved using dielectric-loaded waveguide feeds. Secondly very high values of aperture efficiencies (beyond 91% over a 21% bandwidth) are obtained using printed feeds. The truncation effects of the ground plane and substrate of planar feeds upon the beam characteristics are also studied. We conclude that they must be taken into account at the very first stages of the design process of ILAs.

Focal Array Fed Dielectric Lenses: An Attractive Solution for Beam Reconfiguration at Millimeter Waves

We investigate the radiation capabilities of focal array fed dielectric lens antennas using the FDTD method. Several relevant configurations sharing the same lens architecture (namely an extended hemispherical lens coated with a quarter wavelength matching layer), but illuminated by different sub-array topologies, are compared. In particular, we study the impact of the feeding amplitude coefficients, sub-array size and location upon the radiation patterns and beam scanning performance of the lens. Our numerical results demonstrate that such lens configurations are very attractive and flexible for beam synthesis at millimeter waves (beam shaping, beam scanning and beam reconfiguration). These conclusions are confirmed successfully by several experimental results in Ka-band obtained with a 8 × λ0 lens in Rexolite illuminated by linear printed antenna arrays of variable size.

Design of Wideband Dual Linearly Polarized Transmitarray Antennas

Dual linearly polarized transmitarray antennas with wideband performance are investigated in X-band. Their designs are based on unit-cells with bandpass response. Their structures consist of three conducting layers printed on two identical dielectric substrates glued with a bonding film. Detailed experimental results demonstrate excellent polarization independence, with expected performance and properly preserved radiation characteristics for each polarization. The measured data are in excellent agreement with full-wave simulation results.

Reduced-Size Double-Shell Lens Antenna With Flat-Top Radiation Pattern for Indoor Communications at Millimeter Waves

We investigate the capabilities of reduced-size integrated lens antennas to produce flat-top radiation patterns for broadband wireless communication systems at millimeter waves. The main challenge consists in controlling accurately the lens radiation performance over a broad frequency band while reducing its size; this constitutes a difficult task since producing highly shaped beams usually leads to oversized lens antennas. The design procedure is based on the geometrical optics/physical optics method (GO/PO), and the antenna characteristics are confirmed by full-wave simulations since the antenna size is only a few wavelengths. Our numerical results demonstrate that one anti-reflection coating is necessary even if the lens is made in a low-permittivity material (Rexolite). The resulting double-shell dielectric lens antenna has been fabricated and measured. The experimental results are in very good agreement with the simulations, and the radiation characteristics are stable over a 14% relative bandwidth, which is enough for broadband communications at millimeter waves.

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.

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.

Improvement of the Scanning Performance of the Extended Hemispherical Integrated Lens Antenna Using a Double Lens Focusing System

We demonstrate that an integrated lens antenna (ILA) with a double lens (DL) focusing system can provide simultaneously a high broadside directivity and a low scan loss over a wide angular range. The proposed DL ILA system consists of a hemispherical substrate lens and a planoconvex objective lens. A prototype of a high-gain DL ILA with lenses made of a low permittivity dielectric material is fabricated and characterized in the frequency range of 75-79 GHz. The realized scan loss in terms of gain within a ±30° field of view is <;1.1 dB in both planes. The performance of the DL ILA is compared with that of two hemispherical ILAs designed to provide the best broadside directivity and the lowest scan loss, respectively.

Range of validity and accuracy of the hybrid GO-PO method for the analysis of reduced-size lens antennas: Benchmarking with BoR - FDTD

The range of validity and accuracy of the GO/PO method for the analysis of ILAs has been determined by comparing the GO/PO results to reference data obtained using BoR-FDTD. The internal reflections have been modeled in both cases. Six lens configurations have been considered: two lens diameters (3lambda0 and 6lambda0), and three lens materials (Rexolite, Macor, and Silicon). Our results have shown that GO/PO can be used to study ILAs whose size is typically larger than 4~5lambda0. Additional results obtained with lenses coated with quarter wavelength matching layers will be provided during the conference. In that case, we will show that GO/PO is applicable for slightly smaller lenses.