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

Abstract

International audienceThe 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

Optimization of Micromachined Millimeter-Wave Planar Silicon Lens Antennas With Concentric and Shifted Matching Regions

“…Previously reported lenses typically use matching regions of uniform thickness [3,[9][10][11], here referred to as concentric matching regions. In this paper, we present a new matching region geometry, referred to as a shifted matching region.…”

“…The reported lens antennas have many advantages, including large bandwidths [3], frequency-stable far-fields, beam scanning capabilities [2,6,7] and frequency-stable phase center [3]. Planar lenses have many similarities with non-planar lenses, where there are many good references, see e.g., [8][9][10][11][12][13]. High-resistivity silicon is an excellent dielectric material for millimeter-wave planar lenses, due to its very small losses and accurate micromaching fabrication processes [14,15].…”

“…However, homogeneous lenses of high permittivity materials, such as silicon, suffer from reflections at the airdielectric interface caused by the large difference in impedance compared to free-space (see e.g., [9]). To reduce such reflections, high-permittivity lenses are commonly designed with up to three λ/4-matching regions, i.e., regions with permittivity and thickness determined as single or multiple λ/4-transformers [3,[9][10][11]. The advantages in using up to three λ/4-matching regions for non-planar rotationally symmetric lenses have been described in [11], based on time-domain simulations.…”

“…To reduce such reflections, high-permittivity lenses are commonly designed with up to three λ/4-matching regions, i.e., regions with permittivity and thickness determined as single or multiple λ/4-transformers [3,[9][10][11]. The advantages in using up to three λ/4-matching regions for non-planar rotationally symmetric lenses have been described in [11], based on time-domain simulations. The advantages described in [11] include improved forward-to-backward ratio and reduction of the beam distortions due to ground plane and substrate truncation.…”

“…The advantages in using up to three λ/4-matching regions for non-planar rotationally symmetric lenses have been described in [11], based on time-domain simulations. The advantages described in [11] include improved forward-to-backward ratio and reduction of the beam distortions due to ground plane and substrate truncation.…”