Showing papers on "Reflector (antenna) published in 2017"

Compact Ultrawideband MIMO Antenna With Half-Slot Structure

Abstract: In this letter, a multiple-input–multiple-output (MIMO) antenna with very compact size of only $\text{23}\times \text{18}\; \text{mm}^{2}$ is proposed for ultrawideband (UWB) applications. The proposed MIMO antenna consists of two symmetrical half-slot antenna elements with coplanar waveguide-fed structures and a Y-shaped slot that is cut at the bottom center of the common ground plane. The slot efficiently prevents the current from directly flowing between two ports at low UWB frequency. For such a compact-size antenna, the ground plane works as a radiator as well as a reflector that reflects the radiation from radiators at high frequency. The measured impedance bandwidth for $S_{11}, S_{22}$ $S_{12}, S_{21}$ $S_{12}, S_{21}$ < −20 dB is from 4 to 12.4 GHz. The proposed antenna also contains relatively stable radiation patterns and gains. These performances indicate that the proposed antenna is one competitive candidate for UWB applications.

3-D Absorptive Frequency Selective Reflector for Antenna Radar Cross Section Reduction

Abstract: A methodology for designing a frequency selective reflector with two-sided absorption bands is proposed. This method is based on utilizing multimode resonators inside a 3-D unit cell to obtain an absorption-reflection-absorption response. Detailed analysis of this 3-D absorptive frequency selective reflector (AFSR) is provided with the aid of an equivalent circuit model to reveal the operating principle. To show the benefit of the new structure in antenna’s radar cross section reduction (RCSR), a dual-polarized 3-D-AFSR integrated with monopole and dipole antennas are simulated, fabricated, and then measured. Compared with their counterparts with normal ground plane, AFSR-backed antennas have shown a remarkable out-of-band RCSR. The −10 dB RCSR has fractional bandwidths of at least 64.7% and 41% with center frequencies of 3.4 and 8.3 GHz, respectively. The radiation characteristics of AFSR-backed antennas are nearly maintained. The realized gains are enhanced by 0.9 and 2.3 dB for monopole and dipole antennas mounted on a 3-D-AFSR, respectively.

A Low-Profile Dual-Band Dual-Mode and Dual-Polarized Antenna Based on AMC

Abstract: A low-profile dual-band dual-mode and dual-polarized (DBDMDP) antenna based on artificial magnetic conductor (AMC) is presented in this letter. One reference antenna made of a pair of double-printed crossed dipoles employing vacant quarter-rings is originally realized with dual-band dual-polarized property but strong back radiation. Then, one square-shaped AMC layer is used instead of the metal ground with improved performance. For the lower mode (at 1.38 GHz), the AMC reflection phase of 90° is employed to change the electromagnetic field distribution and achieve monopole-like omnidirectional linear polarization (LP) radiation. Meanwhile for the higher mode (at 1.57 GHz), the AMC with reflection phase of 0° is regarded as a reflector to realize patch-like unidirectional circular polarization (CP) radiation. Thus, probe-single-feed DBDMDP antenna is realized with low-profile property of 0.03λ0, as well as pattern and polarization diversity. One prototype is fabricated to verify the theory analysis, and the measured results reveal that the maximum gain is higher than 2 dBi and 7 dBic for the LP omnidirectional and CP unidirectional modes, respectively. With the advantages of low profile and multifunction, this method offers a good candidate for global position systems applications in the future.

Dual-frequency DRA-based MIMO antenna system for wireless access points

Abstract: An eight-element, dual-frequency, multiple-input-multiple-output (MIMO) antenna system is proposed. Cylindrical dielectric resonator antennas (cDRAs) were used as the radiating elements in the MIMO antenna system. One group of four cDRAs covers the 2.45 GHz band, whereas another four cover the second band at 5.8 GHz. A reflector element was also proposed to tilt the radiated beam patterns and reduce field correlations for the MIMO antenna system. The high-band antenna elements were rotated 45° with respect to their low-band counterparts, on the antenna ground plan, for compactness and printed circuit board integration such that the complete antenna system occupies a volume of 160 mm×160 mm×14.8 mm. The measured bandwidths (BWs) were at least 90 and 200 MHz for the two bands of operation while the envelope correlation coefficient (ECC) was <;0.17. A study of different metallic reflectors was also provided in terms of the impedance matching, isolation, BW, andECC. Specific applications for the proposed design include wireless local area networks and other fourth generation access points.

Liquid-crystal reconfigurable metasurface reflectors

Abstract: This paper presents concept of an electronically beam-steerable flat reflector antennas using liquid-crystal-loaded metasurface. Primary reflector of the proposed antenna concept utilizes metasurface comprising of a large number of reconfigurable true-time-delay (TTD) unit cells. Consequently, reflective phase of the metasurface reflector can be electronically reconfigured in real time to achieve effective beam collimation and beam steering by varying DC voltage distribution of the TTD cells.

Metamaterial Perfect Absorber Analyzed by a Meta-cavity Model Consisting of Multilayer Metasurfaces

Abstract: We demonstrate that the metamaterial perfect absorber behaves as a meta-cavity bounded between a resonant metasurface and a metallic thin-film reflector. The perfect absorption is achieved by the Fabry-Perot cavity resonance via multiple reflections between the “quasi-open” boundary of resonator and the “close” boundary of reflector. The characteristic features including angle independence, ultra-thin thickness and strong field localization can be well explained by this meta-cavity model. With this model, metamaterial perfect absorber can be redefined as a meta-cavity exhibiting high Q-factor, strong field enhancement and extremely high photonic density of states, thereby promising novel applications for high performance sensor, infrared photodetector and cavity quantum electrodynamics devices.

Grating coupler on lithium niobate thin film waveguide with a metal bottom reflector

Abstract: To improve the coupling efficiency between a single-mode fiber and the waveguide on lithium niobate thin film (LNOI), a fiber-to-chip grating coupler with a metal bottom reflector was designed, fabricated, and characterized. A maximum coupling efficiency of −9.1 dB and −6.9 dB for a grating coupler on LNOI without and with a metal bottom reflector was measured, respectively. Fabrication error sensitivity of etch depth was experimentally investigated and the discrepancy between the simulation and experiment was discussed.

Power-flow Conformal Metamirrors for Engineering Wave Reflections

Abstract: Recently, the complexity behind manipulations of reflected fields by metasurfaces has been addressed showing that, even in the simplest scenarios, non-local response and excitation of auxiliary evanescent fields are required for perfect field control. Although these solutions theoretically allow to reflect incident plane waves into any desired direction, actual implementations are difficult and, in most cases, require extensive numerical optimization of the metamirror topology. In this work we introduce purely local reflective metasurfaces for arbitrary manipulations of the power distribution of reflected waves without excitation of any auxiliary evanescent fields. The reflected fields of such local metamirror contain only the desired propagating waves. The method is based on the analysis of the power flow distribution and the adaptation of the reflector shape to the desired distribution of incident and reflected fields. As a result, we find that these power-conformal metamirrors can be easily implemented with conventional passive unit cells.The results can be used for the design of reflecting surfaces with multiple functionalities and for waves of different physical nature. In this work, we present the cases of anomalous reflection and beam splitting, both for acoustic and electromagnetic waves.

A Single Layer Semi-Ring Slot Yagi-Like MIMO Antenna System With High Front-to-Back Ratio

Abstract: A novel two-element single layer semiring slot-based Yagi-like multiple-input-multiple-output (MIMO) antenna system with a compact complementary slot reflector element is presented. This antenna system covers the 3.5 GHz band for WiMAX applications. It has a minimum measured bandwidth of 320 MHz covering from 3.48-3.8 GHz. A simple and compact slot reflector element having the size of 14 x 9.5 mm 2 is used to achieve a minimum measured front-to-back ratio of 10 dB without using additional metallic layers, reflector elements, or any complex back-lobe reduction technique. The total board size of the MIMO antenna system is 80 x 40 x 0.8 mm 3 while the single antenna element has a size of 40 x 40 x 0.8 mm 3 . The antenna system is fabricated and tested. Good agreement is found between simulated and measured results. A measured realized gain of 4.3 dBi, directivity of 6 dB and a minimum measured total radiation efficiency of 73% across the entire band of operation were achieved. This MIMO antenna system has minimum measured isolation of 12 dB, maximum measured envelope correlation value of 0.0385 and diversity gain of 9.81 dB across the entire band of operation.

An integrated model of scintillator-reflector properties for advanced simulations of optical transport.

Abstract: Accurately modeling the light transport in scintillation detectors is essential to design new detectors for nuclear medicine or high energy physics. Optical models implemented in software such as Geant4 and GATE suffer from important limitations that we addressed by implementing a new approach in which the crystal reflectance was computed from 3D surface measurements. The reflectance was saved in a look-up-table (LUT) then used in Monte Carlo simulation to determine the fate of optical photons. Our previous work using this approach demonstrated excellent agreement with experimental characterization of crystal light output in a limited configuration, i.e. when using no reflector. As scintillators are generally encapsulated in a reflector, it is essential to include the crystal-reflector interface in the LUT. Here we develop a new LUT computation and apply it to several reflector types. A second LUT that contains transmittance data is also saved to enable modeling of optical crosstalk. LUTs have been computed for rough and polished crystals coupled to a Lambertian (e.g. Teflon tape) or a specular reflector (e.g. ESR) using air or optical grease, and the light output was computed using a custom Monte Carlo code. 3 × 3 × 20 mm3 lutetium oxyorthosilicate crystals were prepared using these combinations, and the light output was measured experimentally at different irradiation depths. For all reflector and surface finish combinations, the measured and simulated light output showed very good agreement. The behavior of optical photons at the interface crystal-reflector was studied using these simulations, and results highlighted the large difference in optical properties between rough and polished crystals, and Lambertian and specular reflectors. These simulations also showed how the travel path of individual scintillation photons was affected by the reflector and surface finish. The ultimate goal of this work is to implement this model in Geant4 and GATE, and provide a database of scintillators combined with a variety of reflectors.

Semiconductor light-emitting device

Abstract: A light-emitting device comprises a stack structure, wherein the stack structure includes a reflector, a first conductivity-type semiconductor stack layer on the reflector, an active layer on the first conductivity-type semiconductor stack layer, and a second conductivity-type semiconductor stack layer on the active layer; and a first electrode on the stack structure, wherein the stack structure further comprise an oxide layer not exposed to the outer sidewall of the stack structure.

Self-Sensing Electromagnetic Transducer for Vibration Control of Space Antenna Reflector

Abstract: Space antenna reflectors are used by space vehicles to communicate with ground stations. These reflectors are generally subject to broadband random vibration and shock conditions during shipment and vehicle launch. While active vibration control methods can reduce any unexpected responses, sensors, controllers, power amplifiers, and actuators are all required to implement the control system. These additional external devices increase both the weight and the cost of the reflector, and reduce the reliability and safety of the space product. This study proposes a novel self-sensing vibration control method and applies a self-sensing electromagnetic transducer to suppress the vibration of a space antenna reflector. This transducer is used bifunctionally, acting as both an isolator and a velocity sensor. The vibration control principle of the proposed method is analyzed. A governing equation is established using the finite element method. A type of degree of freedom reduction method is used to obtain the response of the space antenna reflector. A ground experiment is then set up. The results demonstrate that the proposed self-sensing vibration control method can reduce the second-order and third-order vibrations of the space antenna reflector by 4 and 9 dB, respectively.

Backlight module and display device

Abstract: The utility model relates to a backlight module and a display device. The backlight module comprises a light-emitting unit, a light guide plate used for receiving light of the light-emitting unit, a reflector plate and a plurality of supporting pieces. The reflector plate is provided with a body part used for bearing the light guide plate and a plurality of side parts, the side parts are arrangedon the periphery of the body part and extend towards the light guide plate in the thickness direction of the light guide plate, and the body part and the side parts jointly define a containing space used for bearing the light guide plate. The supporting pieces are arranged at the corners of the reflector plate respectively, and the structural strength of the supporting pieces is larger than that of the reflector plate. By means of the design that the side edge portion of the reflector plate is bent upwards and the supporting pieces arranged at the corners of the reflector plate, the reflectorplate can replace a traditional back plate and a rubber frame to achieve the function of bearing the light guide plate and other optical elements, the weight of the whole structure is effectively reduced, light leakage can be effectively prevented through the side edge portion of the reflector plate, and the service life of the reflector plate is prolonged. And dust or foreign matters can be prevented from entering the backlight module.

Performance Evaluation of Photovoltaic Solar System with Different Cooling Methods and a Bi-Reflector PV System (BRPVS): An Experimental Study and Comparative Analysis

Abstract: Reducing the price of solar photovoltaic (PV) systems has been a constant challenge. Despite recent advances, solar PV systems are still more costly than conventional energy resources. For the first time, this study examines the effectiveness of three different structures/materials: (i) silvered glass plane mirror; (ii) convex spherical mirrors; and (iii) aluminum (Al) foil as reflector. Comparative analysis of four different cooling techniques, i.e., water sprinkling system, passive heat sink method, active air fan method, and closed loop method, for enhancement of output power was performed. A novel Bi reflector solar PV system (BRPVS) was suggested to control the working of the reflectors. The Al foil enhanced the power output compared to the others. In addition, the effect of using a reflector on the temperature of a solar PV system was studied. High operating temperatures resulted in a decrease in the maximum output power under the same solar radiation conditions. The combined enhancement of the output power by both Al foil BRPVS system and cooling system was almost 22.75–38.55%. An optimal control algorithm to use cooling and BRPVS in an efficient manner is described.

Metamaterial Perfect Absorber Analyzed by a Meta-cavity Model Consisting of Multilayer Metasurfaces

Abstract: We demonstrate that the metamaterial perfect absorber behaves as a meta-cavity bounded between a resonant metasurface and a metallic thin-film reflector. The perfect absorption is achieved by the Fabry-Perot cavity resonance via multiple reflections between the "quasi-open" boundary of resonator and the "closed" boundary of reflector. The characteristic features including angle independence, ultra-thin thickness and strong field localization can be well explained by this model. With this model, metamaterial perfect absorber can be redefined as a meta-cavity exhibiting high Q-factor, strong field enhancement and extremely high photonic density of states, thereby promising novel applications for high performance sensor, infrared photodetector and cavity quantum electrodynamics devices.

Broadband impedance match to two-dimensional materials in the terahertz domain.

Abstract: The coupling of an electromagnetic plane wave to a thin conductor depends on the sheet conductance of the material: a poor conductor interacts weakly with the incoming light, allowing the majority of the radiation to pass; a good conductor also does not absorb, reflecting the wave almost entirely. For suspended films, the transition from transmitter to reflector occurs when the sheet resistance is approximately the characteristic impedance of free space (Z 0 = 377 Ω). Near this point, the interaction is maximized, and the conductor absorbs strongly. Here we show that monolayer graphene, a tunable conductor, can be electrically modified to reach this transition, thereby achieving the maximum absorptive coupling across a broad range of frequencies in terahertz (THz) band. This property to be transparent or absorbing of an electromagnetic wave based on tunable electronic properties (rather than geometric structure) is expected to have numerous applications in mm wave and THz components and systems.

A Hybrid Slot/Monopole Antenna With Directional Heating Patterns for Microwave Ablation

Abstract: We present a new coax-fed interstitial antenna for generating directional heating patterns during microwave ablation. The antenna comprises a base-fed monopole wherein, a portion of the outer conductor is extended to create a reflector that directs the fields toward the opposing direction. To further direct the fields away from the reflector, we etched a semicylindrical slot in the outer conductor. The electric field produced by the slot constructively interferes with the field generated by the monopole in the desired radiation direction, while destructively interfering with the monopole’s field behind the reflector. This creates directional specific absorption rate and heating patterns. In addition, the reflector and slot suppress the unwanted currents along the antennas feeding cable. This eliminates the need for a balun and reduces the overall antenna diameter. The antenna is impedance matched using an internal $\pi $ - matching network. A prototype of this antenna, designed to operate at 7 GHz in egg white, was fabricated and used to perform ablation experiments at a power level of 20 W for 5 min. Experimental results agree well with simulations and confirm the capability of the antenna for generating directional heating patterns.

A Design of an Origami Reconfigurable QHA with a Foldable Reflector [Antenna Applications Corner]

Abstract: This article presents a design of an origami reconfigurable circularly polarized quadrifilar helical antenna (QHA) with a foldable reflector that can operate in K, Ka, and extremely high-frequency (EHF) bands. A 10:1 scale prototype of the proposed antenna is built and validated through measurements and simulations.

Ultraviolet GaN Light-Emitting Diodes with Porous-AlGaN Reflectors.

Abstract: A GaN/AlGaN ultraviolet light emitting diode (UV-LED) structure with a porous AlGaN reflector structure has been demonstrated. Inside the UV-LED, the n+-AlGaN/undoped-AlGaN stack structure was transformed into a porous-AlGaN/undoped-AlGaN stack structure through a doping-selective electrochemical etching process. The reflectivity of the porous AlGaN reflector was 93% at 374 nm with a stop-bandwidth of 35 nm. In an angle-dependent reflectance measurement, the central wavelength of the porous AlGaN reflector had blueshift phenomenon by increasing light-incident angle from 10° to 50°. A cut-off wavelength was observed at 349 nm due to the material absorption of the porous-AlGaN/u-AlGaN stack structure. In the treated UV-LED structure, the photoluminescence emission wavelength was measured at 362 nm with a 106° divergent angle covered by the porous-AlGaN reflector. The light output power of the treated UV-LED structure was higher than that of the non-treated UV-LED structure due to the high light reflectance on the embedded porous AlGaN reflector.

Miniaturized-Element Offset-Feed Planar Reflector Antennas Based on Metasurfaces

Abstract: In this letter, we propose a low-profile planar reflector antenna based on metasurfaces. Metasurfaces are planar version of metamaterials, which are composed of 2-D arrays of subwavelength elements. Due to the subwavelength nature, metasurface-based reflector antenna can be made much thinner and grating lobes can be further suppressed. As an example, a 400 × 400-mm2 offset-fed planar reflector with a focal length $F$ = 300 mm is designed to mould spherical wavefronts into planar ones at 10.0 GHz. The thickness and element spacing is less than λ0 /15 and λ0/6, respectively. Moreover, due to symmetry of the element, the planar reflector is polarization-independent. A prototype was fabricated and measured. Both the simulated and measured results show that the planar reflector antenna can achieve a narrow main lobe and operate over 9.5–10.5 GHz with gain larger than 23 dB.

Coherent control of high efficiency metasurface beam deflectors with a back partial reflector

Abstract: Recently, coherent control of absorption in metallic metasurfaces has been demonstrated, and this phenomenon was applied to intriguing light-by-light switching operation. Here we experimentally demonstrate coherent control of beam deflection by high-efficiency metasurfaces for the first time. Although the beam deflection efficiency by a metasurface is generally small, high-efficiency metasurfaces, which consist of a single layer metasurface with a back reflector, are known to exhibit significantly high deflection efficiency. A key point of our study is to replace the back reflector with a partial reflector instead, which enables light-by-light control of a high-efficiency metasurface with a pair of counter-propagating coherent beam inputs. By adjusting the partial reflector thickness appropriately, the proposed device outperforms ones without a reflector, especially for the deflection efficiency. We finally experimentally demonstrate the expected operation of the fabricated device at a visible wavelength,...

Super directive Yagi-Uda nanoantennas with an ellipsoid reflector for optimal radiation emission

Abstract: In this paper, the optimal designs of silicon Yagi–Uda nanoantennas (NAs) with an ellipsoid reflector have been proposed and analyzed using the 3D finite-difference time-domain method. The combination of nanospheres, nanowires, and ellipsoid reflectors has been employed to enhance the antenna directivity. The nanoantenna geometrical parameters are optimized using the particle swarm optimization algorithm. The optimized spherical NA with an ellipsoid reflector shows high directivity of 19.89, which is higher than the conventional counterpart by 65.75%. This enhancement is attributed to the different supported modes by the ellipsoid reflector, which increases the forward radiation and suppresses the backward one. Further, the optimized nanowire design with an ellipsoid reflector has achieved a directivity of 23.4. In addition, the radiation efficiency has been increased to 80.2% and 75.9% for optimized spherical and nanowire antennas, respectively. This enhancement is attributed to the efficient coupling between array elements as well as reduced sidelobe and back-lobe levels.

Pillow Distortion Analysis for a Space Mesh Reflector Antenna

Abstract: Pillow distortion has become one significant limiting factor to the development of space mesh reflector antennas toward large-scale extension and high surface accuracy However, the current state o

Ultra-thin Bloch-surface-wave-based reflector at telecommunication wavelength

Abstract: We experimentally demonstrate the optical properties of gratings engraved in a single-mode waveguide fabricated on top of a dielectric multilayer platform. The structure can be approached as a reflector for Bloch-surface-wave-based two-dimensional optical systems. The gratings have been fabricated on a thin (∼λ/25) titanium dioxide layer with a thickness of a few tens of nanometers deposited on the top of a multilayer platform. The optical properties of the gratings have been characterized in the near field with the aid of multi-heterodyne scanning near-field optical microscopy. We investigate the surface wave’s interference pattern, produced by incident and reflected light in front of the gratings. The presented gratings behave as an efficient Bloch-surface–wave-based reflector at telecommunication wavelength.

Terahertz High-Gain Offset Reflector Antennas Using SiC and CFRP Material

Abstract: Two high-gain terahertz (THz) offset reflector antennas are proposed. The silicon carbide material and thermally stable carbon fiber-reinforced plastic are selected as reflectors for high specific stiffness and low thermal expansion coefficient which are helpful for space use. Dual polarization is achieved by introducing a wire-grid polarizer which can separate the two THz polarization waves provided by multimode horns fabricated in electroforming technology. Furthermore, three-coordinate test system and theodolites are employed to detect the surface error of dishes and alignment of antenna subsystem. The physical optics analysis based on the measured reflector surface data is introduced referring to the large aperture antenna patterns by virtue of its accuracy and high efficiency. The results of this novel method are compared to that of the near-field test. Measurements show that the sidelobe levels (SLLs) of the single polarization silicon-based reflector are below −32 dB while the gain is 55.3 dB at 330 GHz, and the dual polarization carbon fiber-reinforced plastic reflector antenna suppresses the SLLs to −28 and −29 dB in two principal planes while the gain is 57.2 dB at the same frequency, respectively. The good performances of the proposed antennas indicate the potential for the application of space THz radiometer.

Terrestrial Laser Scanner Two-Face Measurements for Analyzing the Elevation-Dependent Deformation of the Onsala Space Observatory 20-m Radio Telescope's Main Reflector in a Bundle Adjustment.

Abstract: For accurate astronomic and geodetic observations based on radio telescopes, the elevation-dependent deformation of the radio telescopes' main reflectors should be known. Terrestrial laser scanning has been used for determining the corresponding changes of focal lengths and areal reflector deformations at several occasions before. New in this publication is the situation in which we minimize systematic measurement errors by an improved measurement and data-processing concept: Sampling the main reflector in both faces of the laser scanner and calibrating the laser scanner in situ in a bundle adjustment. This concept is applied to the Onsala Space Observatory 20-m radio telescope: The focal length of the main reflector decreases by 9.6 mm from 85 ∘ to 5 ∘ elevation angle. Further local deformations of the main reflector are not detected.