Chapter

Dielectric Lens Antennas

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Abstract

Dielectric lens antennas are attracting a renewed interest for millimeter- and submillimeter-wave applications where they become compact, especially for configurations with integrated feeds usually referred as integrated lens antennas. Lenses are very flexible and simple to design and fabricate, being a reliable alternative at these frequencies to reflector antennas. Lens target output can range from a simple collimated beam (increasing the feed directivity) to more complex multi-objective specifications. This chapter presents a review of different types of dielectric lens antennas and lens design methods. Representative lens antenna design examples are described in detail, with emphasis on homogeneous integrated lenses. A review of the different lens analysis methods is performed, followed by the discussion of relevant lens antenna implementation issues like feeding options, dielectric material characteristics, fabrication methods, and a few dedicated measurement techniques. The chapter ends with a detailed presentation of some recent application examples involving dielectric lens antennas.

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... Dielectric lens antennas are attracting attention from antenna engineers for millimetre wavelengths or shorter wavelength applications where they become compact, especially for configurations with integrated lens antennas [1]. Convex dielectric lenses can increase the radiating aperture and thus antenna gain by transforming spherical waves into planar waveforms [2]. ...
... as discussed in Reference [1]. Similar to (1), Snell's law of refraction is applied at the top surface of the lens as follows: ...
... as discussed in Reference [1]. Similar to (1), Snell's law of refraction is applied at the top surface of the lens as follows: n sin(α) = sin(α + γ) ...
Article
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This paper presents a practical design consideration for the dielectric lens based on Huygens’ principle (HP) at a short distance (=λ0/2) from a feed antenna to overcome the limitation of the conventional design method. It is suggested that certain ranges of dielectric thickness values are not considered to exclude undesired resonant effects that hamper the effectiveness of Huygens’ lens which relies on phase shifting elements. In the proposed HP-based design method, phase distributions are captured at the target distance away from the feed array for the two cases of 2 × 2 and 1 × 4 array antennas and based on these, the proposed lens topology is designed to compensate the phase distributions for gain enhancement. A case study shows that the proposed HP-based design approach considering the actual phase information and undesired dielectric resonant phenomenology can achieve a gain enhancement of up to 5.34 dB compared to the conventional dielectric lens, depending on the feed array arrangement that can render circular or elliptic shapes of phase distributions for radiated fields.
... In order to validate this method, the structure shown in Fig. 4 is simulated in CST Microwave Studio [23], using a dielectric material with r = 2.75, and placing the focus F 1 in different positions between 0 and 10 mm from the end of the DRW. The focal length [24] of the lens is 98.82 mm, the minor and major axes of the ellipse are 50 mm and 110.75 mm, respectively. The length of the dielectric block L block − z (see Fig. 4) is 33.76 mm, and the length of the DRW is ...
... As it was shown in Fig. 1, in a Cassegrain antenna the rays that go towards the main parabolic reflector once reflected by the hyperboloid surface converge at F 2 due to the properties of the hyperbola. However, in the proposed feed, the rays are refracted in the interface between the dielectric and the air, and the propagation direction changes according to their angle of incidence [24]. Thus, the rays towards the main reflector do not converge at a single point but infinite as Fig. 6 depicts. ...
Article
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A dual-reflector antenna with a self-supported subreflector is proposed. The supporting structure is made of dielectric material and it is part of the feeding of the antenna, which is based on Cassegrain optics and works at X-band. The feeding subsystem includes the primary feed, subreflector supporting structure and subreflector surface in a single dielectric piece, resulting in a compact, light and low-cost solution. First, the subreflector and its feeding subsystem, based on a Dielectric Rectangular Waveguide (DRW) along with a hyperboloid, are described, and the phase center of the DRW and the antenna optics are defined. Then, two effective techniques to mitigate the refraction caused by the dielectric were proposed. Finally, the design was validated through the fabrication of a Cassegrain antenna using a 3D printing technique. Measurements and simulations show a very good agreement and an antenna of 26 dBi of directivity with overall very good performances is obtained, validating both the proposed subreflector and the design technique.
... In order to maintain efficient voice and video transmission, there is a requirement for a large bandwidth with a higher gain. Dielectric lens [2] antennas show those characteristics with simple feeding methods. However, those lenses are higher in profile and a have bulky size. ...
Article
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A wideband antenna is proposed based on three-dimensional printing technology. The antenna was designed using the PREPERM 10 material, with permittivity ϵr = 10, where the overall height of the proposed prototype was maintained as 12.83 mm (0.51λ), having a lateral dimension of 60 mm × 60 mm, at an operating frequency of 12 GHz (λ = 25 mm). The proposed antenna achieved a wide frequency bandwidth with a voltage standing-wave ratio (VSWR) of less than two, from 10 GHz to 15 GHz in the Ku-band, where the maximum directivity was 20 dBi over a reflection coefficient bandwidth of 50%. It showed a miniaturized non-uniform metasurface of 2.4λ× 2.4λ× 0.51λ that was placed at 16.5 mm (0.66λ) above the ground plane, which was 2.4λ× 2.4λ× 0.04λ in dimension. Thus, the overall height of the proposed antenna system from the feed source was 29.33 mm (1.17λ). The total weight of the system including the designed structures made of PREPERM 10 and ABS with copper-painted prototypes was 96 g and 79 g, respectively. The measured results were consistent with the simulated results, demonstrating the feasibility and effectiveness of the proposed method.
... Lens antennas whose electromagnetic characteristics vary in space deserve a high interest in the literature because of their potential application to different purposes, starting from the enhancement of antenna performance, to imaging or automotive radar applications [1]. In fact, the peculiar feature of lenses is the manipulation of phase or amplitude (or both), as well as of the primary feed radiation in order to modify the latter according to some initial specification. ...
Article
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The design of spatially varying lens antennas based on artificial materials is of high interest for their wide range of applicability. In this paper, we propose a novel design procedure relying on an inverse formulation of the scattering matrix method (SMM). Differently from many adopted approaches, which resort to global optimizations or homogenization procedures, the inverse SMM (I-SMM) allows the synthesis of optimal parameters (geometrical and/or electromagnetic) for the inclusions realizing the overall device in a very effective manner. With reference to the 2D TM case, the proposed tool has been successfully assessed through the synthesis of different kinds of lenses radiating a pencil beam.
... where λ is the operating wavelength. However, the dielectric material dissipation losses in the lens, which can be estimated by (4) [55], affect the gain ...
Article
In this paper, we propose a ball grid array (BGA) module with an integrated 3D-printed plastic lens antenna for application in a dedicated 130 GHz OOK transceiver that targets the area of 5G backhaul/fronthaul systems. The main design goal was the full integration of a small footprint antenna with an energy-efficient transceiver. The antenna system must be compact and cost-effective while delivering an approximately 30 dBi gain in the working band, defined as 120 GHz to 140 GHz. Accordingly, a 2 ×2 array of aperture-coupled patch antennas was designed in the 7 ×7 ×0.362 mm3 BGA module as the feed antenna of the lens. This achieved a 7.8 dBi realized gain, broadside polarization purity above 20 dB, and over 55% total efficiency from 110 GHz to 140 GHz (20% bandwidth). A plastic elliptical lens 40 mm in diameter and 42.3 mm in height was placed on top of the BGA module. The antenna achieved a return loss better than -10dB and a 28 dBi realized gain from 114 to 140 GHz. Finally, active measurements demonstrated a > 12 Gbps Tx/Rx link at 5 m with BER < 10 -6 at 1.6pJ/b/s. These results pave the way for future cost-effective, energy-efficient, high-data rate backhaul/fronthaul systems for 5G communications.
... It has become even more interesting recently since it has a capability to accurately manufacture functional devices with microscale features with a good repeatability [1]- [4], which is very suitable to microfabricate functional mm-wave and THz components such as dielectric lens antennas [6]- [8], waveguides [9]- [11], sensors [12], and filters/splitters [13]- [17] for realizing low-cost complex THz systems. 3D printing techniques, normally used in mm-wave and THz technologies, are generally classified into five categories: (1) fused deposition modeling (FDM), (2) selective laser sintering (SLS), (3) stereolithographic apparatus (SLA), (4) digital-light-processing (DLP) and (5) polymer jetting (PJ). ...
Article
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In this paper, resin-based photocurable polymer materials for stereolithography (SLA), digital-light-processing (DLP) and polymer-jetting (PJ) additive manufacturing techniques were characterized from 0.2 – 1.4 terahertz (THz) for their comprehensive dielectric properties, e.g. refractive index, absorption coefficient, dielectric constant and loss tangent, by using laser-based THz time-domain spectroscopy (THz-TDS). Fourteen photocurable 3D-printing polymers were chosen owing to their suitability, in terms of printing resolution, material characteristics etc., for millimeter-wave (mm-wave) and THz applications. From the measurement results from 0.2-1.4THz, the dielectric constants of all photopolymer samples under test are between 2.00-3.10 while the loss tangents are from 0.008-0.102, which are quite useful for many applications, e.g. 3D printed antennas and THz transmission lines, which were demonstrated by an asymptotically quasi-single-mode Bragg fiber microfabricated by DLP micromanufacturing technique using HTM140-V2 photopolymer previously reported at the nominal frequencies from 0.246 to 0.276 THz.
... While the first approach is primarily based on the interference phenomenon, the second one utilizes phase accumulation upon propagation. Dielectric lens antennas have been widely studied, and quite sophisticated shapes have been introduced 5,6 . Luneburg lens 7,8 , focusing a plane wave to a point on a spherical surface, is attractive in DoA and other applications, including satellite communications, e.g., [9][10][11][12] . ...
Article
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Direction of arrival (DoA) estimation is of primary importance in a broad range of wireless applications, where electromagnetic waves play a role. While a vast majority of existing techniques is based on phase lag comparison in antenna arrays, intensity-based approaches are valuable in a range of low budget applications. Here we demonstrate a direct visible to a naked eye DoA device, based on a Fresnel zone plate lens, aperture, and a light-emitting diode indicator. Being a low budget device, it still allows achieving up to 90° angle of view, 19° of angular resolution, and 11° of angular accuracy at 10 GHz operational frequency. The demonstrated approach provides fast DoA visualization and can be used to adjust point-to-point communication links, identify radio wave pollution sources at home conditions and several others.
... The chosen profile is a circumference with the feed placed below the circumference centre at a distance z feed . This profile corresponds to a 2D cut of a hyper-hemispheric lens [24]. In this lens type, the feed distance from the centre of the lens is ...
Article
A ball grid array (BGA) module integrated within a three-dimensional printed peanut-shaped lens is proposed for high-data-rate wireless communications in the F-band (116–140 GHz) between a video camera and a TV or a laptop. The module implements a 1 × 2 array antenna which radiates a wide beam in the horizontal plane (H-plane) and a narrower beam in the vertical plane (E-plane). The dielectric lens, fabricated in ABS-M30 plastic, is a shaped lens designed to achieve a fan-beam radiation pattern further narrowing the vertical plane and widening the horizontal plane of the BGA module. The realised gain of the full antenna system is required to exceed 5 dBi within a 120° angular interval in the horizontal plane and a 20° angular interval in the vertical plane. Measurements show a reflection coefficient below −9 dB from 116 to 140 GHz and a maximum realised gain of 8.5 dBi at 130 GHz demonstrating feasibility of the cost-effective proposed design for a high-data-rate communications.
... The extension height h of the hemispherical lens varies depending on the desired radius r and the material permittivity. The height can be calculated by [107] h coll = r √ ε r − 1 (4.5.1) ...
Thesis
Radarbasierte Sicherheitsanwendungen werden in der heutigen Gesellschaft immer wichtiger. Diese können beispielsweise als Abstandsmesser in den verschiedensten Bereichen eingesetzt werden. Bildgebende Systeme können durch eine große Anzahl von Radarmodulen aufgebaut werden. Millimeterwellen bieten im Gegensatz zu herkömmlichen längeren Wellenlängen den Vorteil, dass sie von Objekten, die wenige Millimetern groß sind, reflektiert werden und dennoch in der Lage sind, Partikelwolken zu durchdringen. Höhere Frequenzen in Kombination mit der frequenzmodulierten Dauerstrichradartechnologie haben dabei die Eigenschaft sehr hohe Auflösungen zu erzielen. Jedoch nimmt die Schwierigkeit des Aufbaus von Modulen und der Konstruktion von Antennen für höhere Frequenzen zu, diese wird bedingt durch die notwendige Genauigkeit. Das Ziel der Arbeit ist die Konstruktion und Demonstration der Herstellung von Antennen und vom Aufbau der Module. Es werden Simulationen der Antennen und die dazugehörigen Messungen dargestellt. Mehrere Konzepte für On-Chip- und Off-Chip-Antennen werden vorgeschlagen. Zusätzlich wird für letzteres ein Fertigungsprozess eingeführt. Mögliche Verbesserungen zur Performanz werden ebenfalls diskutiert. Für das System wurde ein umfangreiches Simulationsskript erstellt, welches zur Überprüfung und Untersuchung der Signalintegrität dienen soll. Parallel zum Entwurfsprozess folgen ausgewählte Simulationen des Systems, beginnend bei den niedrigen Eingangsfrequenzen bis hin zu den hohen Frequenzen an der Antenne. Das System wird schließlich mit einer Linse versehe, welche die Abstrahlcharakteristik verbessert und den Aufbau vor grundlegenden äußeren Einflüssen schützt. Die Entwicklung der integrierten Schaltungen sowie die Auswerteelektronik und -algorithmen ist dabei nicht Teil dieser Arbeit. Die einzelnen benutzten Schaltungen werden aber beschrieben. Diverse Messungen charakterisieren die Antennen und die fertigen Module. Am Ende stehen eine neuartige Antenne mit zwei Modulen zur Verfügung, ein Sendemodul und ein Radarmodul, die beliebig als Front-End-Komponenten eingesetzt werden können. Aufgrund der Bauweise können sie wie reguläre Chips auf Leiterplatten platziert und genutzt werden.
... The refraction effects are calculated using Snell law in vector form [16]: ...
Conference Paper
Medical Microwave Imaging (MWI) has been studied as a technique to aid breast cancer diagnosis. Several different prototypes have been proposed but most of them require the use of a coupling medium between the antennas and the breast, in order to reduce skin backscattering and avoid refraction effects. The use of dry setups has been addressed and recent publications show promising results. In this paper, we assess the importance of considering refraction effects in the image reconstruction algorithms. To this end, we consider a simplified homogeneous spherical model of the breast and analytically compute the propagating rays through the air-body interface. The comparison of results considering only direct ray propagation or refracted rays shows negligible impact on the accuracy of the images for moderately high permittivity media. Thus, we may avoid the computational burden of calculating the refracted rays in convex shapes.
... However, the specific form of the classic lens will increase the complexity of the machining process, and is not easy to install. With the rapid improvement on the millimeter and submillimeter wave circuit technology in recent years, there has been a renovated attention on lens antennas (Fernandes et at., 2016), which exhibit a more reasonable dimension at these frequencies. ...
... On the one hand, there are the gradient-index (GRIN) lenses that require different refractive indexes in the lens structure [3,4]. On the other hand, there is the homogeneous lens that is implemented with a single refractive index value, but the shape of the lens defines its focusing performance [5]. ...
Article
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A 3-D printed Fresnel-lens antenna formed by dielectric unit cells insensitive to polarization is presented in this article. The proposed unit cell can be implemented in any azimuth orientation, simplifying the design and the implementation of the Fresnel subzones, which is an advantage over the previous 3-D-printed Fresnel-lens designs. The unit cell exhibits a T-shaped geometry capable of providing no change in relative permittivity under TE polarizations orthogonal to each other. The novel design of the unit cell also provides robustness under oblique incidence and frequency. These features allow the radial arrangement of the unit cells to configure the subzones of the Fresnel lens, ensuring the desired relative permittivity. Additionally, the geometry of the printed unit cells enables self-supported subzones with the minimum number of unit cells per subzone. A 3-D-printed prototype of the proposed Fresnel lens was manufactured by stereolithography (SLA). The measurement results showed a good agreement with the simulated ones. The measured gain was 26.5 ± 0.5 dBi from 55 GHz to 65 GHz with a mean antenna efficiency of 79%.
... However, the generated THz signal requires an additional coupling media to increase the directivity due to the big difference in electric permittivity at the interface GaAs-air. Thus, a bulky silicon lens (Si-lens) is used normally in such THz devices so that certain characteristics of interest, like directivity or modifications in phase or amplitude can be achieved easily 6,7 . However, the bulkiness of these kind of lenses does not allow to have militarized and compact sources for portable applications. ...
Article
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A new integrated lens-antenna is designed and implemented for a nanocontact based terahertz (THz) photomixer. The new design replaces the standard conventional bulky silicon lens, which normally no THz photomixer can avoid. The Fresnel Zone Plate is used to design the new lens-antenna and is simulated by the MIT open-source tool called Meep. The final design showed, with only two simple fabrication technology processing steps (standard optical lithography) that the lens-antenna can be monolithically integrated with the THz nanophotomixer. With its compact design, the THz measurements showed a comparable behavior to the conventional bulky silicon lens, therefore it would be ready for photonic integrated circuits based THz systems.
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Article
In this paper, the design and analysis of a seven port radar duplexer for tracking a target in X-band operation are presented. The S-parameters of the structure are calculated and compared with experimental results. The simulations and experimental results are in good agreement. This device enables radars to calculate the horizontal difference, vertical difference and sum of four beams of a monopulse antenna based on amplitude discriminator. Three magic-Ts and one T-junction are used, four input ports are connected to a monopulse antenna and three other ports are output ports. The output data give three equations between input signals that allow the radar to track a target. Results show that the S-parameters of this device are affected by magic-Ts and the T-junction structure, and an optimum structure for magic-Ts and the T-junction is proposed. A comprehensive study has been carried out for determination and comparison of properties of the structure in theory, simulation and experimental results. This device is useful in radar tracking systems.
Chapter
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Chapter
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During the past years, various research teams developed 60 GHz chipset solutions, using both advanced CMOS [1] and BiCMOS [2] technologies. But for the 60 GHz market to flourish not only low cost RFICs are required, low cost antennas and packages are also key elements. Recently, low cost High Density Interconnect (HDI) organic technology has been evaluated [3, 4] to develop 60 GHz module using antenna-in-package approach. Measured gain is in the order of 4 dBi but there is still a need to achieve higher gain in order to increase the transmit/receive range of the system. The use of a lens is an appealing solution since it enables to customize the system performances while using existing chipset solution. In this paper, we investigate the performances achievable by a plastic (ABS-M30) lens manufactured using low cost and rapid manufacturing 3D printing technology. Material properties at 60 GHz are reviewed, a preliminary 60 GHz lens design is detailed and the full system is validated using a WiGig wireless link (demonstrating a 10 dB improvement in the link budget in comparison with the system without lens).
Article
The great flexibility offered by transformation optics for controlling electromagnetic radiation by virtually re-shaping the electromagnetic space has inspired a myriad of dream-tailored electromagnetic devices. Here we show a 3D-transformed microwave Luneburg lens antenna which demonstrates high directivity, low side-lobe level, broadband response and steerable capabilities. A conventional Luneburg lens is redesigned accounting for dielectric materials that implement a coordinate transformation, modifying the lens geometry to accommodate its size and shape for easy integration with planar microwave antenna applications. An all dielectric lens is manufactured following a thorough holistic analysis of ceramic materials with different volume fractions of bi-modal distributed titanate fillers. Fabrication and measurements of a 3-D flat Luneburg lens antenna validate the design and confirm a high-directivity performance. A directivity of 17.96 dBi, low side-lobe levels for both main planes ~ -26 dB, excellent directivity performance within the X-band and beam-steering up to 34 ° were achieved.
Article
In this work, we designed, built, and tested a low-gain 20 dBi Luneburg Lens antenna using a rapid prototyping machine as a proof of concept demonstrator. The required continuously varying relative permittivity profile was implemented by changing the size of plastic blocks centered on the junctions of a plastic rod space frame. A 12-cm ( 4λ0 at 10 GHz) diameter lens is designed to work at X-band. The effective permittivity of the unit cell is calculated by effective medium theory and simulated by full-wave finite-element simulations. The fabrication is implemented by a polymer jetting rapid prototyping method. In the measurement, the lens antenna is fed by an X-band waveguide. The measured gain of the antenna at X-band is from 17.3 to 20.3 dB. The measured half-power beam width is from 19° to 12.7° while the side lobes are about 25 dB below the main peak. Good agreement between simulation and experimental results is obtained.
Article
We introduce a novel procedure to retrieve the complex permittivity of dielectric materials. It is a variant of the well-known waveguide method, and uses as input the one-port reflection data from a vector network analyzer connected to a short circuited rectangular waveguide filled with a dielectric sample of known length. Here, it is shown that for low to moderate loss materials, the locus of the reflection coefficient in the complex plane versus frequency is approximately a circumference arc with curvature radius that depends mainly on the imaginary part of the permittivity and such that the swept angle depends mostly on real part. It is proven that fitting the theoretical circumference arc with the measured data not only allows identifying possible measurement errors but also enables estimating the complex permittivity with good accuracy. A graphical based implementation of the method is described and validated experimentally.
Conference Paper
Scanning properties of a quarter-sphere Luneburg lens with two backing ground planes are evaluated. The main beam of the antenna is scanned by rotating the feed antenna, as in a full or a hemispherical lens antennas. Since only one quarter of the lens is used the weight of the antenna is halved compared to a hemispherical lens. This reduction is achieved at the expense of the scanning range of the antenna. Simulated results for a small quarter-sphere two-layer lens operating at 20 GHz are presented, showing that scanning loss of less than 0.5 dB may be achieved in the range of ±50° in the azimuth plane and ±25° in the elevation plane.
Article
In this paper, a 3-D integrated 77-GHz automotive radar front-end is presented. Embedded wafer level packaging (EMWLP) technology is proposed to eliminate the use of wire bonding, which not only introduces significant radio frequency loss, but also occupies large footprint for high-pin count die. The transceiver bare die is embedded in a reconfigured molded wafer with compression molding process. Double-sided multiple redistribution layers are formed to fan-out the transceiver input/output signals and through mold via is employed to realize the vertical interconnection. With these promising features, the EMWLP technology can be extended to a 3-D integration. A substrate integrated waveguide slot antenna is integrated on top of the EMWLP module and a lens is used to enhance the antenna directivity. The performance of the fully integrated radar front-end is tested and the measurement results show good package performance with RF loss around 5 dB for most of the samples. Temperature cycling reliability test was also performed by letting the fully integrated prototype goes through 1000 temperature cycles with JEDEC standard. The measured package loss spread across samples after 1000 cycles of TC test is about 13 dB, which is mainly due to the antenna warpage affecting the RF path's signal integrity.
Article
This letter presents design of E-band integrated lens antennas (ILAs) with two-dimensional (2-D) fully electronical beam-steering capability. Two extended hemispherical quartz lenses with the radii of 7.5 and 12.5 mm and a feeding printed circuit board (PCB) with 16 aperture-coupled microstrip antenna (ACMA) elements arranged in a 2-D order together with a switching circuit were fabricated for experimental verification. A set of the directivity and radiation patterns measurements of the scanning antenna at 77 and 85 GHz is presented. It is shown that the ILA with the radius of 12.5 mm provides the coverage within the solid angle in any direction from the lens axis with the directivity not lower than 20 dBi in the covered area. The ILA with the radius of 7.5 mm provides higher coverage (within ), but with the lower directivity of 16 dBi. A good agreement between the electromagnetic simulations and the measurements is demonstrated. The designed ILAs can be effectively used in different millimeter-wave applications such as WLAN/WPAN communications, automotive radars, imaging systems, and millimeter-wave radio backhaul systems.
Article
This paper examines the performance of dual-linear sinuous antennas on silicon extended hemispherical silicon dielectric lenses. A theoretical impedance of 106 Ω is identified based on the analysis of an ideal self-complementary structure, and this result compares well with simulations and measurements. The radiation properties of a linearly polarized sinuous antenna are simulated using Method of Moments software coupled to a GO/PO code, and also agree well with measurements. The results indicate that the sinuous antenna is an excellent wideband planar feed for a silicon lens, with cross-polarization levels below -17 dB, and polarization variations of ±5° over two octaves in frequency. The application areas are millimeter-wave, wideband, dual-polarized radio-astronomy receivers.
Article
We have been developing a terahertz camera based on antenna-coupled superconducting resonators, the so-called microwave kinetic inductance detectors (MKIDs), and a silicon lens array. The MKID consists of a coplanar waveguide coupled to a double slot antenna and is patterned on a high-quality aluminum film grown by molecular beam epitaxy. The camera is sensitive at frequencies of 200-240 GHz. Its bandwidth is limited by the impedance properties of the double slot antenna. The design, fabrication, and optical evaluations of the planar antennas and silicon lens arrays are presented in this paper. The MKID camera has been evaluated both in dark conditions and under optical radiation in a 0.1-K dilution refrigerator. The electrical noise equivalent power was around 5×10-18 W/√(Hz) in dark conditions and 4×10-16 W/√(Hz), which is much lower than the photon noise level, with the optical load. The optical efficiency of the camera was estimated by three independent methods, and the results were consistent with each other and equal to 20%-25% without an anti-reflection coating on the lens surface.
Article
In this paper, we present the design, fabrication, and measurements of a lens THz antenna that can be fabricated using conventional photolithography and deep reactive etching processes. The antenna is composed of an extended hemispherical silicon lens and a leaky wave waveguide feed. Both elements are fabricated using silicon micromachining techniques, enabling the fabrication of future large antenna arrays with a parallel process. To show the concept, a first antenna prototype has been fabricated using this fabrication process. Measurements obtained at 550 GHz are presented.
Article
This paper presents design and experimental verification of electronically steerable integrated lens antennas (ILAs) for WLAN/WPAN communication systems operating in the 60-GHz frequency band. The antenna is comprised of a quartz extended hemispherical lens, four switched aperture coupled microstrip antenna (ACMA) elements, and a distribution circuit based on SPDT MMIC switches. The designed ILAs are capable of electronic steering between four different antenna main beam directions in one plane. Fixed beam and electronically steerable ILA prototypes are fabricated and tested. The results are given for two quartz dielectric lenses with the radii of 7.5 and 12.5 mm in order to meet a wide range of WLAN/WPAN requirements. The measured maximum gains of the designed ILAs are 18.4 and 23.2 dBi. The experimental results of the fabricated electronically steerable quartz ILA prototypes prove the simulation results and show ±35° and ±22° angle sector coverage for the lenses with the 7.5 and 12.5 mm radii, respectively. The bandwidth of the ILAs exceeds the frequency band of 57-66 GHz allocated for WLAN/WPAN applications. The designed ILAs meet all the requirements for steerable directional antennas of 60-GHz WLAN/WPAN systems.
Article
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.
Article
We describe the performance of a flat shaped dielec- tric 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 method- ology 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%.
Article
Cosecant squared cell illumination may contribute to enhance system performance in MM-wave wireless communication systems. Previously proposed axial symmetric dielectric lens antennas produce a most useful constant flux circular footprint, but they fail to cover the regions near the vertices of square cells. This paper presents a simplified procedure to design a 3D dielectric lens that produces a constant-flux square foot print, intended for the illumination of square or rectangular cells. Calculated and measured antenna performance is presented not only in terms of radiation pattern, but also in terms of coverage, and time dispersion
Article
An automated open resonator system designed and constructed for precision measurement of loss tangent and dielectric permittivity of low absorbing materials at 60 GHz is reported. The use of a high-Q hemispherical Fabry-Perot cavity together with highly stabilized synthesized phase-locked Gunn oscillator sources and the superheterodyne receiver enabled a loss tangent value as low as 10 μrad to be measured. The system is automated by means of a precision lock-in amplifier, a V-band Hewlett-Packard spectrum analyzer and a Hewlett-Packard Vectra computer system with analog-to-digital conversion accessories. The synthesizer allows the collection of data at very small steps over the complete Gaussian beam, and, together with a statistical fitting, the Q determination can be made very accurately
Book
Principles of Optics is one of the classic science books of the twentieth century, and probably the most influential book in optics published in the past forty years. This edition has been thoroughly revised and updated, with new material covering the CAT scan, interference with broad-band light and the so-called Rayleigh-Sommerfeld diffraction theory. This edition also details scattering from inhomogeneous media and presents an account of the principles of diffraction tomography to which Emil Wolf has made a basic contribution. Several new appendices are also included. This new edition will be invaluable to advanced undergraduates, graduate students and researchers working in most areas of optics.
Article
The Luneberg lens enables easy beam scanning and has the possibility of multibeam forming. In order to apply these characteristics to a planar antenna, it is first necessary to discuss a method of fabrication for a thin-plate Luneberg lens. On the other hand, there is a method of controlling permittivity whereby many holes having diameters sufficiently smaller than the wavelength are created in the dielectric material. Permittivity control by the hole density has been used as a method of adjusting the permittivity over a wide range in order to realize a matching layer for the lens, by creating many holes in the direction perpendicular to the incident electric field or close to this direction. In contrast, the authors propose a method for adjusting the permittivity over a wide range by creating multiple holes parallel to the electric field. By means of the hole density method, a Luneberg lens is fabricated. The operating characteristics are determined at 10 and 48 GHz. It is confirmed that the structure works well as a Luneberg lens at both frequencies. Further, as an example of the applications of the plate Luneberg lens, a parallel plate slot array antenna is fabricated and its radiation characteristics are measured. It is found that the Luneberg lens can be applied as the feed section of a high-gain millimeter-wave planar antenna with a beam scanning capability. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(9): 1–12, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1120
Conference Paper
This paper describes the design and use of an open Fabry-Perot resonator to evaluate the degree of anisotropy of dielectric material samples at millimeter-waves. The proposed implementation not only allows identifying the orientation of the dielectric principal axes but also determining the complex permittivity values along these axes.
Article
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.
Conference Paper
This paper presents the new software tool - ILASH - that was developed at IT under contract for ESA-ESTEC. The set of powerful tools for double-shell lens design, analysis, optimization and diagnosis along with its Windows-based user-friendly interface make the ILASH tool unique. ILASH software tool proved to be reliable, accurate and very versatile. It not only enables the lens design, but the wide range of possible analysis and diagnosis tools allows a complete insight on the lens properties and limitations.
Conference Paper
This paper proposes a new shaped double-material lens for this objective and presents its design and performance when integrated into the reflector system. A parabolic reflector is used to prove the lens concept. Reflector optimization is out of the scope of this paper. Experimental results are presented for a fabricated scaled lens prototype at 62.5 GHz.
Article
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.
Conference Paper
One critical performance parameter associated with feed systems for reflectors or other focused antennas is the feed phase center position. Maximum aperture efficiency is obtained when the feed phase center is positioned at the reflector focal point. Although horn antennas are the most common feeds for reflectors, lens antennas with bolometer detectors integrated at its base are the most common configuration [1] at millimeter and, especially, at sub-millimeter waves imaging and radiometric applications. Unlike horns, where the phase center position is normally located close to the aperture plane, the phase center of integrated lenses is very dependent upon the lens shape and may even be far out from the lens body. However, when bolometers or other detectors are used at the lens under test, only amplitude measurements can be obtained, preventing the usual phase center calculation from radiation pattern phase information. In this communication an alternative procedure based on power measurements is proposed and evaluated. Corresponding results obtained for a double-shell dielectric lens are compared to those obtained for the same lens with the usual method based on measured phase pattern. The alternative method uses an auxiliary collimated lens and can be used in small anechoic chambers.
Article
We present an antenna engineering approach to significantly improve off-axis detection properties of terahertz focal plane arrays (FPAs) behind an extended-hemispherical lens. In particular, antennas in the off-axis pixels in a large FPA were redesigned to exhibit tilted receiving patterns. The new antenna structure corrects for beam distortions in off-axis sensors due to the small lens size. Specifically, this approach is well suited for monolithic antenna structures integrated with high-sensitivity heterostructure backward diodes. Although the approach is demonstrated for 100- and 500-GHz FPAs, the presented technique is equally applicable to other planar antenna topologies and sensor materials that operate well into the terahertz regime. In addition, standard RF impedance-matching techniques were used to improve responsivity performance of the diode-coupled FPAs. The beam-correction techniques allow for a factor-of-5 larger size FPA for a fixed lens size. We also note that a tradeoff between Gaussicity and directivity becomes necessary for larger lenses. Thus, increasing the size of the FPA, without resorting to increasing the lens size, enables improved coupling efficiencies (Gaussicity) as well as better pixel resolution (directivity).
Article
The recently introduced transformation-electromagnetics techniques provide a new methodology for designing devices that possess novel wave-material interaction properties. They are based on the form invariance of Maxwell's equations under coordinate transformations. These methods provide an extremely versatile set of design tools that employ spatial-coordinate transformations, where the compression and dilation of space in different coordinate directions are interpreted as appropriate scalings of the material parameters. The most famous transformation-optics device is the cloak of invisibility. However, a wide variety of other devices are also possible, such as field concentrators, polarization rotators, beam splitters, beam collimators, and flat lenses. In this paper, an overview of transformation-electromagnetics device design techniques is presented. The paper begins by introducing the underlying design principle behind transformation electromagnetics. Several novel transformation-based device designs are then summarized, starting with electromagnetic cloaks that have spherical shell or cylindrical annular shapes, More general cloaking designs of noncircular annular geometries are treated, and the application of cloaking to RF/microwave antenna shielding is also discussed. Following this, device designs that employ transformations that have discontinuities .on the domain boundary are presented. Unlike those used for cloaks, this type of transformation is capable of modifying the fields outside of the device. Examples of this type of transformation-electromagnetics device are presented, which include flat near-field and far-field focusing lenses, wave collimators for embedded sources (e.g., antennas), polarization splitters and rotators, and right-angle beam benders.
Article
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%.
Article
An accurate computer-aided-design tool has been developed for the synthesis of broadband layered circular-cylindrical dielectric lens antennas. It is based on the combination of a fast method of analysis formulated in the spectral domain with a global optimization algorithm based on the particle swarm optimization technique. Using this tool, the influence of the number of layers is studied for lenses of moderate size. We show that single-layer lenses with an optimum permittivity value have nearly the same radiation characteristics as optimized multi-layer configurations. Finally we introduce a new height reduction technique that allows reducing the lens size by almost a factor of two while retaining the fan-beam pattern capabilities of cylindrical lenses in the elevation plane as well as their axial-symmetry needed for beam scanning in the horizontal plane. Numerical results have been compared successfully with experimental ones from 26 to 40 GHz, to validate the analysis.
Article
The effects of parasitic air gaps on the input impedance and radiation characteristics of dense double-shell integrated lens antennas are studied numerically at millimetre waves using the finite-difference time-domain method. The lens core is made up of Macor or silicon, and is coated with a quarter wavelength matching layer. Two kinds of gaps are compared: they are located either (i) between both shells of the lens, or (ii) between the lens base and the feed substrate. We show that their impact is much more critical in the second case, and that it becomes dramatic for silicon lenses, even with very thin gaps (smaller than ¿ <sub>0</sub>/100); the three major observed effects are the following: (i) strong shift of the resonant frequency, (ii) beam broadening and directivity loss, (iii) increase of the side lobe level.
Article
This letter presents a new broadband printed antenna based on crossed exponential slot configuration, which presents very good linear polarization. It is compact and especially adequate for integrated lens antenna feeding at millimeter waves and submillimeter waves. The concept is validated with experimental results.
Article
This paper presents the design and evaluation of a high dielectric constant double-material integrated lens antenna for multi-beam or scanning applications. The lens is formed by two shaped embedded shells of different material permittivity to enhance both power transmission across the lens interfaces and the lens scanning characteristics over a broad frequency range, when the feeds are integrated at the lens base. Design is based on Geometrical Optics formulation and the lens performance is evaluated using the classic hybrid Geometrical Optics / Physical Optics approach (GO/PO). The proposed lens concept is experimentally validated with a fabricated MACOR/Acrylic prototype, showing less than 1 dB scan loss up to ±20º with Gaussissity better than 95% over 40% frequency band at millimeter-waves.