Showing papers on "Reflector (antenna) published in 2019"

Highly efficient GaN-based high-power flip-chip light-emitting diodes

Abstract: High-power flip-chip light-emitting diodes (FCLEDs) suffer from low efficiencies because of poor p-type reflective ohmic contact and severe current crowding. Here, we show that it is possible to improve both the light extraction efficiency (LEE) and current spreading of an FCLED by incorporating a highly reflective metallic reflector made from silver (Ag). The reflector, which consists of an Ag film covered by three pairs of TiW/Pt multilayers, demonstrates high reflectance of 95.0% at 460 nm at arbitrary angles of incidence. Our numerical simulation and experimental results reveal that the FCLED with Ag-based reflector exhibits higher LEE and better current spreading than the FCLED with indium-tin oxide (ITO)/distributed Bragg reflector (DBR). As a result, the external quantum efficiency (EQE) of FCLED with Ag-based reflector was 6.0% higher than that of FCLED with ITO/DBR at 750 mA injection current. Our work also suggests that the EQE of FCLED with the Ag-based reflector could be further enhanced 5.2% by replacing the finger-like n-electrodes with three-dimensional (3D) vias n-electrodes, which spread the injection current uniformly over the entire light-emitting active region. This study paves the way towards higher-performance LED technology.

Wearable Electromagnetic Head Imaging System Using Flexible Wideband Antenna Array Based on Polymer Technology for Brain Stroke Diagnosis

Abstract: Given the increased interest in a fast, portable, and on-spot medical diagnostic tool that enables early diagnosis for patients with brain stroke, a new approach of a wearable electromagnetic head imaging system based on the polymer material is proposed. A flexible low-profile, wideband, and unidirectional antenna array with electromagnetic band gap (EBG) and metamaterial (MTM) unit cells reflector is utilized. The designed antenna consists of a 4 × 4 radiating patch loaded with symmetrical extended open-ended U-slots and fed by combination of series and corporate transmission lines. A mushroom-like 10-EBG unit cell arrays are arranged around the feeding network to reduce surface waves, whereas 4 × 4 MTM unit cells are placed on the back-side of the antenna to enable unidirectional radiation. The antenna is designed and embedded on a multilayer low cost, low loss, transparent, and robust polymer poly-di-methyl-siloxane (PDMS) substrate and optimized to operate in contact with the human head. The simulated and measured results show that the antenna has a fractional bandwidth of 53.8% (1.16–1.94 GHz), more than 80% of radiation efficiency, and satisfactory field penetration in the head tissues with a safe specific absorption rate. An eight-element array is then configured on 300 × 360 × 4.1 mm3 PDMS material covering an average human head size and used as a worn part of the imaging system. A realistic-shaped 3-D specific anthropomorphic mannequin (SAM) head phantom is used to verify the performance of the designed array. The imaging results indicate the possibility of using the designed conformal array to detect a bleeding inside the brain using a confocal image algorithm.

Progress in the design and the applications of linear Fresnel reflectors – A critical review

Abstract: Solar concentrating power is one of the most promising ways of producing clean electricity by utilizing the incident solar irradiation on the earth. Linear Fresnel reflector (LFR) is one of the major concentrating solar systems for producing useful heat in medium and high-temperature levels (

A Dual-Polarized Frequency-Reconfigurable Low-Profile Antenna With Harmonic Suppression for 5G Application

Abstract: A dual-polarized frequency-reconfigurable low-profile antenna with harmonic suppression for 5G application is presented in this letter. The proposed design consists of a pair of ±45° polarized frequency-reconfigurable dipole antennas, two vertically placed feeding structures with filtering branches, and an artificial magnetic conductor (AMC) surface. By introducing the U-shaped structure, a better impedance matching performance is achieved in two bands. Measured results show that the proposed antenna can operate at 3.24–4.03 and 4.44–5.77 GHz by controlling the on–off of PIN diodes, and port isolation of two bands is greater than 25 dB. What is more, two-octave harmonic suppression is realized by loading the filtering branches. In order to obtain stable unidirectional radiation pattern in the operating bands and low-profile characteristic, a dual-band 4 × 4 AMC reflector is fabricated. Finally, a maximum gain of 6.86 dBi in low frequency band and 8.14 dBi in high frequency band are obtained. Besides, the height of the proposed antenna is 0.1 λ at 3.3 GHz. Experimental results show that the antenna can meet the needs of the 5G communication.

Low-RCS Reflectarray With Phase Controllable Absorptive Frequency-Selective Reflector

Abstract: This paper presents a methodology to control the reflection phase response from a 3-D bandstop structure backed with an absorbing material. An absorptive frequency-selective reflection structure using the cascaded arc-shaped strip resonators and absorbers is utilized to obtain an absorption–reflection–absorption response. The reflection phase response of the structure within the reflection band is then flexibly controlled by top-loaded metallic patches with variable size. An application of this methodology is demonstrated by designing a high-gain and low-radar cross section (RCS) reflectarray. The in-band phase profile of the reflecting surface is constructively designed to collimate the beam in the far field. Meanwhile, the out-of-band scattering from the planar reflector is significantly reduced. Compared with a conventional reflectarray, the radiation performance of the proposed antenna is maintained with an aperture efficiency of 50.1% and directivity of 23.5 dBi. Significant RCS reduction has been achieved with a fractional bandwidth of 76.9% and 17.1% for the lower and upper bands with reduction levels of 10 and 8 dB, respectively.

A Low-Profile, Dual-Polarized Patch Antenna for 5G MIMO Application

Abstract: A dual-polarized patch antenna with an extremely low profile is proposed in this communication. It consists of a main radiator, an annulus, and a reflector. The main radiator contains two pairs of differentially driven feedlines and an irregular patch. These differentially driven feedlines are utilized to coupled feed the irregular patch through a small gap, which has distinguished feature compared with other designs. It turns out that a resonance at 3.55 GHz is generated. Then, an annulus is set above the main radiator to compensate the inductive component induced by the main radiator and generate the other resonant point. As a result, the dual-polarized antenna could work from 3.3 to 3.6 GHz with the extremely compact size of $0.29\lambda _{\mathbf {0}} \times 0.29\lambda _{\mathbf {0}} \times 0.06\lambda _{\mathbf {0}}$ . ( $\lambda _{0}$ is the free-space wavelength at 3.45 GHz.) The simulated isolation and cross-polarization discrimination at 0° of the antenna element reach more than 35 and 44 dB. The simulated front-to-back ratio of co-polarization and cross-polarization is larger than 44 and 22 dB, separately. To verify the design, a prototype of the $2\times 2$ array based on the element is fabricated and measured. The results show that the antenna has high potential in the fifth-generation (5G) massive multiple-input multiple-output application.

Compact Air-Filled Luneburg Lens Antennas Based on Almost-Parallel Plate Waveguide Loaded With Equal-Sized Metallic Posts

Abstract: This paper presents a Luneburg lens and a Luneburg reflector lens along with the corresponding compact and cost-effective multibeam antennas in the Ka -band. The Luneburg lens is composed of an air-filled parallel plate waveguide (PPW) loaded with equal-sized metallic posts. The upper plate of the PPW is designed to a curved surface to meet the requirement of the equivalent refractive index profile, meanwhile providing a transition between the lens and the feed waveguide. Also, based on the law of reflection, a reflecting wall is introduced to the Luneburg lens to achieve a Luneburg reflector lens. By employing the WR28 rectangular waveguides as the feeders, the Luneburg lens/reflector lens antennas with single beam and multiple beams are designed and experimentally verified in the whole Ka -band. The multibeam Luneburg lens antenna show the beam scanning from −45° to +45° with 0.6 dB scan loss. The multibeam Luneburg reflector lens antenna show the beam scanning from 30° to 60° with 0.7 dB scan loss. Besides, the acceptable performances of aperture efficiency, impedance matching and multiport isolation are achieved. The results indicate that the works in this paper have application potential in the millimeter-wave (mmW) wireless communications.

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, nonlocal response and excitation of auxiliary evanescent fields are required for perfect field control. 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 field. 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 for both acoustic and electromagnetic waves.

Challenges in On-Chip Antenna Design and Integration with RF Receiver Front-End Circuitry in Nanoscale CMOS for 5G Communication Systems

Abstract: This paper investigates design considerations and challenges of integrating on-chip antennas in nanoscale CMOS technology at millimeter-wave (mm-wave) to achieve a compact front-end receiver for 5G communication systems. Solutions to overcome these challenges are offered and realized in digital 28-nm CMOS. A monolithic on-chip antenna is designed and optimized in the presence of rigorous metal density rules and other back-end-of-the-line (BEoL) challenges of the nanoscale technology. The proposed antenna structure further exploits ground metallization on a PCB board acting as a reflector to increase its radiation efficiency and power gain by 37.3% and 9.8 dB, respectively, while decreasing the silicon area up to 30% compared to the previous works. The antenna is directly matched to a two-stage low noise amplifier (LNA) in a synergetic way as to give rise to an active integrated antenna (AIA) in order to avoid additional matching or interconnect losses. The LNA is followed by a double-balanced folded Gilbert cell mixer, which produces a lower intermediate frequency (IF) such that no probing is required for measurements. The measured total gain of the AIA is 14 dBi. Its total core area is 0.83 mm 2 while the total chip area, including the pad frame, is 1.55 × 0.85 mm 2 .

Compact UWB FSS reflector for antenna gain enhancement

Abstract: In this study, two compact ultra-wideband (UWB) frequency selective surface (FSS) reflectors, which combine the branch loading method with the design of the traditional FSS, are proposed for antenna gain enhancement application. The working mechanism of the proposed FSS reflectors is analysed by the equivalent circuit model. The first FSS reflector, which is a 10 × 10 array with 8.25 mm × 8.25 mm unit size, not only enhances the gain of the UWB antenna, but also guarantees a constant gain with only 0.5 dB variation across the whole operation band. To further reduce the reflector size, a more compact FSS reflector with 6.25 mm × 6.25 mm unit size is designed by printing similar patterns on both sides of a single-layer dielectric slab. Compared to the first structure, the second reflector can realise a 25% size reduction and the same gain variation in the entire UWB frequency range. The only compromise is a 0.5 dB gain decrease. Finally, a good agreement between the measured and simulated results proves the feasibility of the authors' design.

A Circular Polarized Feed Horn With Inbuilt Polarizer for Offset Reflector Antenna for $W$ -Band CubeSat Applications

Abstract: A novel $W$ -band left-hand circular polarized (LHCP) cylindrical waveguide feed horn antenna is proposed. The proposed antenna features an inbuilt polarizer structure and a single side-fed linear polarized input to offer symmetric LHCP radiation pattern. The internal polarizer structure consists of nine pairs of circular cavities to generate a circularly polarized wave, eliminating the need for an orthomode transducer or a complex septum. The side-fed horn reduces the overall length by eliminating the rectangular to circular waveguide transition. The proposed horn antenna’s electrical dimension is $7.2\lambda \times 3.9\lambda \times 1.4\lambda $ at 84 GHz. The antenna has impedance matching ( $S_{11}$ below −15 dB) and axial ratio below 1.2 dB from 79.5 to 88 GHz. The horn is used as a feed source for an offset parabolic reflector of 10 cm diameter and small $f/D$ ratio 0.25, which can fit inside a CubeSat. The reflector antenna provides the simulated right-hand circular polarization (RHCP) directivity of 36.6 dBic at 86 GHz with spillover loss of 0.83 dB. The feed reflector assembly is also simulated with the complete aluminum CubeSat chassis. The measurement of the prototyped feed horn and the offset parabolic reflector antenna validates the analysis and simulation results.

Low-RCS Reflectarray Antenna Based on Frequency Selective Rasorber

Abstract: We design a low-radar-cross-section (RCS) planar reflectarray antenna by using a frequency selective rasorber (FSR). Due to the metal-backed configuration and focusing effect of the phase modulation surface, the RCS of a planar reflectarray antenna is generally quite high. Besides, an out-of-band signal focused by the reflector may cause serious interference to the system and affect the performance of facilities. To reduce the RCS of the reflectarray and suppress out-of-band interference, the FSR with a transmission window is designed and covered in front of the reflectarray. Simulation results show that the out-of-band RCS of the reflectarray is significantly reduced without affecting the radiation performance. To verify the benefits of the structure in antenna's RCS reduction (RCSR) and interference suppression, the reflectarray, the FSR, and the horn antenna work at 8.9 GHz are designed, fabricated, and measured. Measurement results show that the gain of the proposed low-RCS reflectarray antenna has only 0.3 dB decrease compared with the gain of non-FSR configuration. Meanwhile, the RCS of the proposed structure is remarkably reduced, and the –10 dB RCSR is obtained from 4 to 12.5 GHz.

Collimated Beam FMCW Radar for Vital Sign Patient Monitoring

Abstract: Patient monitoring of vital signals such as breathing rhythm and heartbeat rate can be done remotely by the use of a radar system. This approach is advantageous since it does not require any contact with the patient. Obviously, contactless monitoring results in a more comfortable situation for the patient, and in occasions, it is almost mandatory as in the case of heavy burned or newborn patients. Moreover, additional information such movement patterns are also available. A 120 GHz frequency modulated continuous wave radar is described with special focus on the design, construction, and testing of a specific reflector antenna for the system. The system is based on a commercial radar chipset that includes its own antennas. The challenge has been to design the optimum reflector and to build it and test it in a cost-effective way. The reflector has been 3-D printed and a near-field testing technique has been implemented to assess its performance. The results show that the system is able to measure the vital signs at distances beyond 1 m.

Wide-band Beam-scanning by Surface Wave Confinement on Leaky Wave Holograms.

Abstract: A two-dimensional (2-D) metasurface design for backward leaky wave suppression in microwave regime is proposed based on the theory of holography. The so-called Rabbit's ears phenomenon describes that the backward mode in the reference wave plays the destructive role and makes the holography principle to behave properly mainly in an only narrow frequency interval. Here, we explore the utilization of the surface wave reflectors to suppress the backward mode to achieve wide-band holograms. Therefore, the reference wave form is manipulated by the choice of various reflector shapes and some providing forward mode dominant reference wave are analyzed and simulated. The less backward mode participates in the reference wave; the wider operation frequency range is obtained. With the canceled Rabbit's ears phenomenon, variations in the reference wave frequency cause elevation angle scan. The results provide general insights into relation of the Rabbit's ears phenomenon and the object wave accuracy in frequencies except the design frequency. The idea is also applied to multiple object wave holograms. The concept is verified using both electromagnetic full-wave simulations and experimental measurements.

Flexible thermal responsive infrared reflector based on cholesteric liquid crystals and polymer stabilized cholesteric liquid crystals.

Abstract: In this study, we fabricated a temperature-responsive infrared reflector that adjusts to temperature changes by changing its transmittance of incident IR light. The device utilized a thermally induced change in the pitch of a cholesteric liquid crystal (CLC) to achieve near-infrared light reflection in a particular wavelength range. In addition, a polymer-stabilized cholesteric liquid crystal (PSCLC) was used as an alternative to further optimize the device performance. Polyethylene terephthalate (PET) was used as the substrate material to allow the reflector to be flexible. The light transmission performance of the reflector at different bending angles was explored, and no significant effect was found. A simulated solar device was established to study the temperature regulation effects of both CLC and PSCLC devices.

Design and Development of High-Gain SIW H-Plane Horn Antenna Loaded With Waveguide, Dipole Array, and Reflector Nails Using Thin Substrate

Abstract: In this communication, a new probe-fed substrate integrated waveguide (SIW) H-plane horn antenna including three linear dipole arrays is proposed. To feed the dipole arrays, a portion of a rectangular waveguide is placed at the front of the radiating aperture of the SIW horn in conjunction with two slots, which are etched at the top and bottom of the substrate. A row of reflector nails is also added to reduce the backward radiation and to improve the antenna gain. A prototype of the proposed antenna is fabricated using the printed circuit board process. The proposed antenna is numerically investigated by a software package. The simulated and measured results are reported for verification. The measured results show that the proposed antenna provides 13.97 dBi gain at 20.5 GHz with a low backward radiation.

5G multi-element/port antenna design for wireless applications:a review

Abstract: Fifth generation (5G) is the current hot topic of the world's leading telecommunication companies. The compact designs of antennas made it possible for them to resonate at higher frequencies, thus to enable the devices to attain higher data rate as compared to 4G technology. Data rate of 5G technology for low mobility users is expected to be 50.0 Gbps and for high mobility users it is 5.0 Gbps. On the other hand, International telecommunication union's objective for 5G is 3 times more spectrally efficient thanlong-term evolution (LTE). The paper has carried out meticulous study over the impact of 5G antennas on the size of antenna, size/type of substrate, gain, efficiency, and isolation, etc. Also, different arrays andmultiple input multiple outputs (MIMOs) with patch antenna, magneto electric-dipole, microstrip grid array antenna, folded dipole, series-fed array, connected antenna array, MIMO are studied. The paper also includes the existing technology i.e 4G LTE and their isolation enhancement approaches. Many of the designs used the reflector plates to reduce the back lobe radiation problem in MIMO/array antennas to increase front-to-back ratio. The gain in 5G antennas can be increased by using balun, parasitic element as directors, multiple notch structures, three identical slot sub-arrays, etc. Mathematical equations of multi-element/port antennas are included to model the designed antennas. The beam steering is also included for the 5G technology in this paper.

Active shape control of an antenna reflector using piezoelectric actuators

Abstract: The surface precision of an antenna reflector can be improved using the actuation of piezoelectric materials to obtain a high-performance space antenna. In this study, the active shape control of a...

An ultra-wide band low-SAR flexible metasurface-enabled antenna for WBAN applications

Abstract: In this study, an ultra-wideband low-specific absorption rate (SAR) flexible metasurface-enabled wearable antenna is proposed for wireless body area network applications. The antenna and metamaterial (MM) structure were designed and analyzed using a commercial electromagnetic simulation software program which uses a finite integration technique solver. The antenna is designed and fabricated on a jeans textile substrate in the size of 58 × 80 × 1 mm3. Moreover, MM reflector was designed on a felt textile substrate to reduce the SAR effect of the antenna and to increase the antenna performance (such as impedance matching, radiation pattern, and realized gain) parameters. Designed and fabricated antenna parameters and the SAR value results with and without MM are investigated. The simulated peak SAR values when the antenna with MM is placed on the body model are 0.86, 0.198, and 0.103 W/kg at frequencies of 4 GHz, 7 GHz, and 10 GHz, respectively, for 10 g of tissue. The simulated peak SAR value of the antenna with MM is also reduced by a percentage of 97, compared to the simulated peak SAR value of the antenna without MM. The peak SAR values of the antenna were less than the European safety limit of 2 W/kg for 10 g of tissue when the MM was used as an isolator. Furthermore, the simulated peak realized gain value of the antenna with the MM was increased by 98% (from 4.6 to 9.1 dB) compared to the simulated peak realized gain value of the antenna without MM. Simulation and measurement results showed that performance characteristics and peak SAR values of the proposed antenna were suitable and safe for wearable technologies.

Dynamics of Antenna Reactive Energy Using Time-Domain IDM Method

Abstract: A general computational paradigm, the time-domain infinitesimal dipole model (IDM) method, is developed and applied to compute reactive energy and radiated power for arbitrary shaped antennas with different time-domain excitations. The proposed technique first utilizes finite-difference time-domain method to compute the time-domain radiating antenna currents from near-zone electric/magnetic fields. Further, the far-zone time-domain radiated power is analytically estimated using a suitable IDM of the antenna spacetime current distributions. The time-domain reactive energy is calculated by adopting a rigorous energy subtraction approach. The proposed time-domain IDM technique is first validated by reproducing the standard antenna-Q-factor results of half-wavelength thin-wire dipoles. Second, time-domain reactive energy signatures are obtained for pulse-excited single and multiband dipole antennas, both in isolated condition and two-element multi-in multi-out (MIMO) topology. Third, the effects of parasitic reflector and director elements on the spatio-temporal energy dynamics of thin-wire Yagi–Uda antennas are demonstrated. The proposed algorithm is very general, applicable to arbitrary antenna shape and spacetime excitations, and hence is expected to enable engineers to look beyond traditional single frequency Q-factors of electrically small antennas to probe into the more fundamental spatio-temporal energy dynamics of general radiating structures, especially future generation 5G MIMO antennas.

Multichannel Staggered SAR: System Concepts With Reflector and Planar Antennas

Abstract: In the context of radar spaceborne imaging, the novel multichannel staggered synthetic aperture radar (SAR) mode represents a promising solution for the mapping of ultrawide swaths with very high azimuth resolution. This paper extends the analysis of multichannel staggered SAR to planar antenna architectures and provides system design examples both for planar and reflector antenna architectures. Furthermore, a first proof of concept using measured data acquired by an experimental ground-based system is provided to demonstrate the approach's feasibility.

Advanced Multibeam Antenna Configurations Based on Reflectarrays: Providing multispot coverage with a smaller number of apertures for satellite communications in the K and Ka bands

Abstract: This article presents some recent developments in multiplebeam antennas (MBAs) based on reflectarrays for communication satellites in the Kurz (K) and Kurz-above (Ka) bands. The existing high-throughput satellites commonly employ four reflector antennas to provide cellular coverage that is formed by multiple spot beams in a four-color scheme. Reflectarray antennas are proposed as an attractive solution for the design of novel MBA configurations to produce multispot coverage, with a smaller number of apertures than conventional MBA systems based on reflector technology. Single and dual reflectarray configurations have been considered for the purpose of exploiting their ability to produce independent beams in different polarizations and frequencies.