Showing papers on "Reflector (antenna) published in 2015"

Indoor position location using delayed scanned directional reflectors

Abstract: A mobile device determines its location accurately by measuring the range to a position reflector as well as azimuth and elevation angles of arrival (AOA) at the reflector. The mobile can transmit a coded radar signal and process reflections to determine its location. The reflectors may include internal delays that can identify the reflector and provide transmit/receive separation for the mobile. The reflection can include a primary and further delayed secondary reflection. The mobile can determine the internal delay of the reflector based on the delay between primary and secondary reflections. The range and AOA information can be combined with information about the position, orientation, and characteristics of the reflectors to determine location. In some systems, the mobile device can determine its location in a three-dimensional space using reflections from only one reflector. The reflectors, which can be economically produced, can be unpowered and low profile for easy installation.

Functional metamirrors using bianisotropic elements.

Abstract: Conventional mirrors obey the simple reflection law that a plane wave is reflected as a plane wave, at the same angle. To engineer spatial distributions of fields reflected from a mirror, one can either shape the reflector or position some phase-correcting elements on top of a mirror surface. Here we show, both theoretically and experimentally, that full-power reflection with general control over the reflected wave phase is possible with a single-layer array of deeply subwavelength inclusions. These proposed artificial surfaces, metamirrors, provide various functions of shaped or nonuniform reflectors without utilizing any mirror. This can be achieved only if the forward and backward scattering of the inclusions in the array can be engineered independently, and we prove that it is possible using electrically and magnetically polarizable inclusions. The proposed subwavelength inclusions possess desired reflecting properties at the operational frequency band, while at other frequencies the array is practically transparent. The metamirror concept leads to a variety of applications over the entire electromagnetic spectrum, such as optically transparent focusing antennas for satellites, multifrequency reflector antennas for radio astronomy, low-profile conformal antennas for telecommunications, and nanoreflectarray antennas for integrated optics.

Antenna having a reflector for improved efficiency, gain, and directivity

Abstract: An antenna having at least one reflector for improving radiation efficiency, gain, and directivity is disclosed. The antenna may be formed on a substrate or be a standalone conductive material that is designed to operate in at least one band of frequency. The antenna includes a reflector for each band of frequency the antenna is designed to operate in. The reflector is positioned relative to the antenna to redirect electromagnetic radiation of the antenna away from surrounding materials or objects that affect, i.e., reflect, refract, diffract, absorb and scatter the antenna's electromagnetic radiation.

Electrically switchable polymer stabilised broadband infrared reflectors and their potential as smart windows for energy saving in buildings

Abstract: Electrically switchable broadband infrared reflectors that are relatively transparent in the visible region have been fabricated using polymer stabilised cholesteric liquid crystals. The IR reflectors can change their reflection/transmission properties by applying a voltage in response to changes in environmental conditions. Simulations predict that a significant amount of energy can be saved on heating, cooling and lighting of buildings in places such as Madrid by using this switchable IR reflector. We have also fabricated a switchable IR reflector which can also generate electricity. These polymer based switchable IR reflectors are of high potential as windows of automobiles and buildings to control interior temperatures and save energy.

Advanced Antenna Technologies for Satellite Communications Payloads

Abstract: A review of various antenna technologies suitable for satellite communications and applicable to fixed satellite, broadcast satellite, mobile communications, and personal communications services is presented. Antenna technologies suitable for generating contoured beam and multiple-beam antennas are reviewed. Design considerations for reflector antennas and feed assemblies and antenna performance in terms of coverage gain, sidelobe isolation, and cross-polar isolation are discussed. Current and future technological trends are presented in the above areas.

Metasurface external cavity laser

Abstract: A vertical-external-cavity surface-emitting-laser is demonstrated in the terahertz range, which is based upon an amplifying metasurface reflector composed of a sub-wavelength array of antenna-coupled quantum-cascade sub-cavities. Lasing is possible when the metasurface reflector is placed into a low-loss external cavity such that the external cavity—not the sub-cavities—determines the beam properties. A near-Gaussian beam of 4.3° × 5.1° divergence is observed and an output power level >5 mW is achieved. The polarized response of the metasurface allows the use of a wire-grid polarizer as an output coupler that is continuously tunable.

A Directional Interstitial Antenna for Microwave Tissue Ablation: Theoretical and Experimental Investigation

Abstract: Microwave ablation (MWA) is a minimally invasive thermal therapy modality increasingly employed for the treatment of tumors and benign disease. For successful treatment, complete thermal coverage of the tumor and margin of surrounding healthy tissue must be achieved. Currently available interstitial antennas for MWA have cylindrically symmetric radiation patterns. Thus, when treating targets in proximity to critical structures, caution must be taken to prevent unintended thermal damage. A novel coaxial antenna design for MWA with an asymmetrical cylindrical heating pattern is presented in this paper. This radiation pattern is achieved by employing a hemicylindrical reflector positioned at a critical distance from a conventional coaxial monopole antenna. Finite-element method simulations were employed to optimize the geometric dimensions of the antenna with the objective of minimizing the antenna reflection coefficient at the 2.45-GHz operating frequency, and maximizing volume of the ablation zone. Prototype antennas were fabricated and experimentally evaluated. Simulations indicated an optimal S 11 of –32 dB at 2.45 GHz in close agreement with experimental measurements of –29 dB. Ex vivo experiments were performed to validate simulations and observe effects to the antennas’ heating pattern with the varying input power and geometry of the reflector. Ablation zones up to 20 mm radially were observed in the forward direction, with minimal heating (less than 4 mm) behind the reflector.

Sardinia Radio Telescope: General Description, Technical Commissioning and First Light

Abstract: In the period 2012 June–2013 October, the Sardinia Radio Telescope (SRT) went through the technical commissioning phase. The characterization involved three first-light receivers, ranging in frequency between 300MHz and 26GHz, connected to a Total Power back-end. It also tested and employed the telescope active surface installed in the main reflector of the antenna. The instrument status and performance proved to be in good agreement with the expectations in terms of surface panels alignment (at present 300μmrms to be improved with microwave holography), gain (∼0.6K/Jy in the given frequency range), pointing accuracy (5 arcsec at 22GHz) and overall single-dish operational capabilities. Unresolved issues include the commissioning of the receiver centered at 350MHz, which was compromised by several radio frequency interferences, and a lower-than-expected aperture efficiency for the 22-GHz receiver when pointing at low elevations. Nevertheless, the SRT, at present completing its Astronomical Validation phase...

Reflector Antenna Developments: A Perspective on the Past, Present and Future

Abstract: i»?Reflector antennas confine most of the electromagnetic energy captured over their apertures into a focal plane or redirect the radiated field of the feed into far field. This paper presents a concise history of reflector antenna developments over an extended time span. Representative examples are provided for different periods that impacted various developments of reflector antennas covering past, present, and future. Due to page limitations, not all worldwide aspects of reflector antenna developments are touched upon in this paper, and the authors have confined themselves to the areas that have influenced their research activities.

Optical Design of Multisource High-Flux Solar Simulators

Abstract: We present a systematic approach to the design of a set of high-flux solar simulators (HFSSs) for solar thermal, thermochemical, and materials research. The generic simulator concept consists of an array of identical radiation modules arranged in concentric rows. Each module consists of a short-arc lamp coupled to a truncated ellipsoidal specular reflector. The positions of the radiation modules are obtained based on the rim angle, the number of concentric rows, the number of radiation modules in each row, the reflector radius, and a reflector spacing parameter. For a fixed array of radiation modules, the reflector shape is optimized with respect to the source-to-target radiation transfer efficiency. The resulting radiative flux distribution is analyzed on flat and hemispherical target surfaces using the Monte Carlo ray-tracing technique. An example design consists of 18 radiation modules arranged in two concentric rows. On a 60-mm dia. flat target area at the focal plane, the predicted radiative power and flux are 10.6 kW and 3.8 MW m(-2), respectively, and the predicted peak flux is 9.5MW m(-2).

Slotted ground microstrip antenna with FSS reflector for high-gain horizontal polarisation

Abstract: The design of a high-gain horizontally polarised antenna for ultra-wideband (UWB) operation is presented and experimentally demonstrated. Gain enhancement is achieved by using a frequency selective surface (FSS) reflector. Both the antenna and the FSS have simple structures and are printed on a similar substrate. The antenna is a three-stepped narrow rectangular slot excited using a three-stepped microstrip feed line. By optimising the lengths and widths of the sections of the slot and the feed line, an ultra-wide impedance bandwidth (3.2–12 GHz, measured) has been achieved. The FSS is a two-layer structure where each layer is an array of rectangular patches printed on one side of the substrate. With the application of the FSS, the antenna gain is enhanced by 3–4 dBi over most of the band. The polarisation purity (in terms of the measured cross-polar difference) is also improved with the FSS. Such an antenna–FSS combination will be useful for high-gain UWB applications requiring horizontal polarisation.

A High Efficient Reflectarray Antenna Consisted of Periodic All-Metallic Elements for the Ku-band DTV Applications

Abstract: This letter presents the design of a reflectarray antenna consisted of metallic elements, which can be manufactured via the simple die casting process as that for the reflector antennas. In the design, the reflecting elements are integrated as a whole piece of metal without using any dielectric or air substrates, and result in very high radiation efficiency at a low manufacture cost. The antenna is prototyped at Ku-band for the civilian satellite DTV applications. The experimental results show a radiation efficiency up to 90% comparable to the reflector antennas, and demonstrate the feasibility of the design concept.

Phased Array Fed Reflector (PAFR) antenna architectures for space-based sensors

Abstract: Communication link and target ranges for satellite communications (SATCOM) and space-based sensors (e.g. radars) vary from approximately 400–1000 km for low earth orbits (LEO) to 35,800 km for geosynchronous orbits (GEO). At these long ranges, large antenna gains are required and most legacy systems use high gain reflectors with beams that are either fixed or mechanically steered. However, for some radio frequency (RF) sensor applications, mechanical beam scanning has inherent limitations.

Particle manipulation by a non-resonant acoustic levitator

Abstract: We present the analysis of a non-resonant acoustic levitator, formed by an ultrasonic transducer and a concave reflector. In contrast to traditional levitators, the geometry presented herein does not require the separation distance between the transducer and the reflector to be a multiple of half wavelength. The levitator behavior is numerically predicted by applying a numerical model to calculate the acoustic pressure distribution and the Gor'kov theory to obtain the potential of the acoustic radiation force that acts on a levitated particle. We also demonstrate that levitating particles can be manipulated by controlling the reflector position while maintaining the transducer in a fixed position.

Theoretical analysis and design guideline for focusing subwavelength gratings

Abstract: We propose a planar dielectric reflector with focusing ability using concentric circular subwavelength gratings (CC-SWGs). The two-dimensional focusing ability of CC-SWGs is investigated by the rigorous coupled-wave analysis (RCWA) and finite element method (FEM). By designing the concentric circular pattern of the grating surface, a focusing reflector with high numerical aperture (NA) and high reflectivity is constructed. A CC-SWG reflector with a diameter of 32.6μm and a focal length of 6μm is investigated, which exhibits high focusing ability at normal incidence with a radially polarized plane wave. At the reflection focal plane, the full-width-half-maximum (FWHM) of the electric field intensity is 0.89μm. Numerical aperture value as high as 0.93 is achieved for the reflector with very high reflectivity of 92%.

Eliminating the azimuth ambiguity in single-well imaging using 3C sonic data

Abstract: The shortcomings of conventional single-well sonic imaging are the inefficiency in eliminating azimuth ambiguity of the reflector outside boreholes. To resolve this problem, we proposed that 3C data of the reflection echoes be migrated simultaneously. The quantitative expressions of the received 3C data were first derived. The direct correlations between the polarity of the 3C data and the reflector azimuth were analyzed. It was revealed that the reflector positions can be fully identified by the associated echoes consisting of the transverse and axial components of wavefields. And an improved single-well imaging procedure using axial displacement component in addition to transverse components was thus developed. Numerical examples were evaluated for validation of the imaging method. According to the numerical results, the image intensity of the reflectors was effectively enhanced whereas the artificial mirrors of the reflectors were greatly weakened. It was suggested that a sonic logging tool with the 3C receivers be necessary for the image of reflectors without azimuth ambiguity.

High-efficiency photon capturing in ultrathin silicon solar cells with front nanobowl texture and truncated-nanopyramid reflector.

Abstract: We present a crystalline siliconthin-film (5 μm) solar cell decorated by a front nanobowled texture and a rear truncated-nanopyramid silver reflector. This design substantially suppresses the overall light reflection and enhances the optical resonances inside the silicon film leading to the photon-capturing performance comparable to the Yablonovitch limit. We show that optical absorption can be greatly improved by adjusting the ratio of the periods between the rear and front nanostructures with an optimal ultimate photocurrent density around 35.3 mA/cm2 and an enhancement of 42.6% relative to the planar counterpart. A thorough optoelectronic simulation predicts the light-conversion efficiency of around 15.5%, i.e., 67.3% higher than that of the planar system.

Improved area-based deformation analysis of a radio telescope’s main reflector based on terrestrial laser scanning

Abstract: Abstract The main reflectors of radio telescopes deform due to gravitation when changing their elevation angle. This can be analyzed by scanning the paraboloid surface with a terrestrial laser scanner and by determining focal length variations and local deformations from best-fit approximations. For the Effelsberg radio telescope, both groups of deformations are estimated from seven points clouds measured at different elevation angles of the telescope: the focal length decreases by 22.7 mm when tilting the telescope from 90 deg to 7.5 deg elevation angle. Variable deformations of ± 2 mm are detected as well at certain areas. Furthermore, a few surface panels seem to be misaligned. Apart from these results, the present study highlights the need for an appropriate measurement concept and for preprocessing stepswhen using laser scanners for area-based deformation analyses. Especially, data reduction, object segmentation and laser scanner calibration are discussed in more detail. An omission of these steps would significantly degrade the deformation analysis and the significance of its results. This holds for all sorts of laser scanner based analyses.

Acoustophoretic device with piezoelectric transducer array

Abstract: An apparatus for separating particles from a fluid stream includes a flow chamber that has at least one inlet and at least one outlet. At least one ultrasonic transducer is located on a wall of the flow chamber. The transducer includes a piezoelectric array with at least two piezoelectric elements. The piezoelectric array includes a piezoelectric material to create a multi-dimensional acoustic standing wave in the flow chamber. A reflector is located on the wall on the opposite side of the flow chamber from the at least one ultrasonic transducer.

Performance of Archimedean spiral antenna backed by FSS reflector

Abstract: The use of a backing cavity composed of a frequency selective surface (FSS) above a metal plate as a means to suppress the back lobe radiation and increase the gain of an Archimedean spiral antenna that operates from 3 to 10 GHz is investigated. The FSS is designed to reflect signals in the upper band (7–10 GHz) with a loss of <0.25 dB, and allow transmission in the lower band (3–6 GHz). Good impedance match and bidirectional to unidirectional beam transformation is obtained when the FSS and metal plate are inserted at a distance λ/4 below the spiral at the centre of the upper and lower bands, respectively. Simulated and measured radiation patterns are employed to show the performance enhancement, which is attributed to the FSS reflector.

Inflatable antenna for cubesat: Extension of the previously developed s-band design to the X-band

Abstract: The inflatable antenna for CubeSat is a 1 meter antenna reflector designed with one side reflective Mylar, another side clear Mylar with a patch antenna at the focus. The development of this technology responds to the increasing need for more capable communication systems to allow CubeSats to operate autonomously in interplanetary missions. An initial version of the antenna for the S-Band was developed and tested in both anechoic chamber and vacuum chamber. Recent developments in transceivers and amplifiers for CubeSat at X-band motivated the extension from the S-Band to the X-Band. This paper describes the process of extending the design of the antenna to the X-Band focusing on patch antenna redesign, new manufacturing challenges and initial results of experimental tests.

Room-temperature continuous-wave operation of membrane distributed-reflector laser

Abstract: In this paper, we report on the first ever demonstration of a continuous-wave operation of an injection-type membrane distributed-reflector (DR) laser at room temperature. A threshold current of 250 µA was obtained with a stripe width of 0.7 µm, a DFB region length of 30 µm, and a DBR region length of 90 µm. An external differential quantum efficiency of 11% with a light output ratio between the front and the rear of 6.7 was obtained at the front waveguide.