Showing papers on "Radio wave published in 2016"

Generating multiple orbital angular momentum vortex beams using a metasurface in radio frequency domain

Abstract: In this paper, an electromagnetic metasurface is designed, fabricated, and experimentally demonstrated to generate multiple orbital angular momentum (OAM) vortex beams in radio frequency domain. Theoretical formula of compensated phase-shift distribution is deduced and used to design the metasurface to produce multiple vortex radio waves in different directions with different OAM modes. The prototype of a practical configuration of square-patch metasurface is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that multiple OAM vortex waves can be simultaneously generated by using a single electromagnetic metasurface. The proposed method paves an effective way to generate multiple OAM vortex waves in radio and microwave wireless communication applications.

Performance of two Askaryan Radio Array stations and first results in the search for ultrahigh energy neutrinos

Abstract: Ultrahigh energy neutrinos are interesting messenger particles since, if detected, they can transmit exclusive information about ultrahigh energy processes in the Universe. These particles, with energies above 1016 eV, interact very rarely. Therefore, detectors that instrument several gigatons of matter are needed to discover them. The ARA detector is currently being constructed at the South Pole. It is designed to use the Askaryan effect, the emission of radio waves from neutrino-induced cascades in the South Pole ice, to detect neutrino interactions at very high energies. With antennas distributed among 37 widely separated stations in the ice, such interactions can be observed in a volume of several hundred cubic kilometers. Currently three deep ARA stations are deployed in the ice, of which two have been taking data since the beginning of 2013. In this article, the ARA detector “as built” and calibrations are described. Data reduction methods used to distinguish the rare radio signals from overwhelming backgrounds of thermal and anthropogenic origin are presented. Using data from only two stations over a short exposure time of 10 months, a neutrino flux limit of 1.5 × 10−6 GeV=cm2=s=sr is calculated for a particle energy of 1018 eV, which offers promise for the full ARA detector.

Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

Abstract: We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principle calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.

A Reconfigurable Graphene Reflectarray for Generation of Vortex THz Waves

Abstract: A reconfigurable graphene reflectarray is proposed for the generation of vortex radio waves at THz. First, a simple sectored circular reflective surface model with a plane wave at normal incidence is constructed to illustrate how vortex radio waves can be generated. Then, a graphene reflective cell is examined to demonstrate that the reflection coefficient can be controlled by changing the chemical potential and size of the graphene patch. Next, the sectored circular reflective surface is realized with the graphene reflective cells that are properly sized, arranged, and biased to satisfy the required reflection coefficients for various modes of vortex radio waves. Finally, the graphene reflectarray is excited with a horn antenna, showing from simulations that it can be dynamically reconfigured to generate the 0, $\pm 1$ , and $\pm 2$ modes of vortex radio waves at 1.6 THz.

LEAP: the large European array for pulsars

Abstract: The Large European Array for Pulsars (LEAP) is an experiment that harvests the collective power of Europe's largest radio telescopes in order to increase the sensitivity of high-precision pulsar timing. As part of the ongoing effort of the European Pulsar Timing Array (EPTA), LEAP aims to go beyond the sensitivity threshold needed to deliver the first direct detection of gravitational waves. The five telescopes presently included in LEAP are: the Effelsberg telescope, the Lovell telescope at Jodrell Bank, the Nan\c cay radio telescope, the Sardinia Radio Telescope and the Westerbork Synthesis Radio Telescope. Dual polarization, Nyquist-sampled time-series of the incoming radio waves are recorded and processed offline to form the coherent sum, resulting in a tied-array telescope with an effective aperture equivalent to a 195-m diameter circular dish. All observations are performed using a bandwidth of 128 MHz centered at a frequency of 1396 MHz. In this paper, we present the design of the LEAP experiment, the instrumentation, the storage and transfer of data, and the processing hardware and software. In particular, we present the software pipeline that was designed to process the Nyquist-sampled time-series, measure the phase and time delays between each individual telescope and a reference telescope and apply these delays to form the tied-array coherent addition. The pipeline includes polarization calibration and interference mitigation. We also present the first results from LEAP and demonstrate the resulting increase in sensitivity, which leads to an improvement in the pulse arrival times.

Millimetre Wave with Rotational Orbital Angular Momentum

Abstract: Orbital angular momentum (OAM) has been widely studied in fibre and short-range communications. The implementation of millimetre waves with OAM is expected to increase the communication capacity. Most experiments demonstrate the distinction of OAM modes by receiving all of the energy in the surface vertical to the radiation axis in space. However, the reception of OAM is difficult in free space due to the non-zero beam angle and divergence of energy. The reception of OAM in the space domain in a manner similar to that in optical fibres (i.e., receiving all of the energy rings vertical to the radiation axis) is impractical, especially for long-distance transmission. Here, we fabricate a prototype of the antenna and demonstrate that rather than in the space domain, the OAM can be well received in the time domain via a single antenna by rotating the OAM wave at the transmitter, i.e., the radio wave with rotational OAM. The phase and frequency measured in the experiment reveal that for different OAM modes, the received signals act as a commonly used orthogonal frequency division multiplexing (OFDM) signal in the time domain. This phase rotation has promising prospects for use in the practical reception of different OAMs of millimetre waves in long-distance transmission.

Composite materials for supersonic aircraft radomes with ameliorated radio frequency transmission-a review

Abstract: Encompassment of radar communication in modern avionics provides the backbone for safe flight and tactical warfare. In the past few decades radar technology has achieved commendable precision and sophistication, but efficient communication relies upon effective transmission of electromagnetic waves through materials shielding the antenna and exhibiting high transparency for radio/microwaves. Since the structure of radomes in supersonic aircraft is dominated by aerodynamic standards, numerous challenges are encountered while selecting the materials apposite for construction having superior mechanical strength and resilience while displaying the minimum influence on the transmission profile of radio waves. The radome structure of aircrafts is subjected to sudden acceleration, drag forces and erosion due to rain and dust, which change the transmission characteristics due to change in shape/thickness of the structure. The problems are further complicated by the advent of supersonic/hypersonic aircrafts and missiles where high strength preservation and structural integrity is necessary at temperatures in excess of 350 °C. This review systematically throws light on the composite materials and existing technologies employed for the fabrication of high strength, low dielectric loss sandwich radomes for supersonic aircrafts.

Space-based aperture array for ultra-long wavelength radio astronomy

Abstract: The past decade has seen the advent of various radio astronomy arrays, particularly for low-frequency observations below 100 MHz. These developments have been primarily driven by interesting and fundamental scientific questions, such as studying the dark ages and epoch of re-ionization, by detecting the highly red-shifted 21 cm line emission. However, Earth-based radio astronomy observations at frequencies below 30 MHz are severely restricted due to man-made interference, ionospheric distortion and almost complete non-transparency of the ionosphere below 10 MHz. Therefore, this narrow spectral band remains possibly the last unexplored frequency range in radio astronomy. A straightforward solution to study the universe at these frequencies is to deploy a space-based antenna array far away from Earths’ ionosphere. In the past, such space-based radio astronomy studies were principally limited by technology and computing resources, however current processing and communication trends indicate otherwise. Furthermore, successful space-based missions which mapped the sky in this frequency regime, such as the lunar orbiter RAE-2, were restricted by very poor spatial resolution. Recently concluded studies, such as DARIS (Disturbuted Aperture Array for Radio Astronomy In Space) have shown the ready feasibility of a 9 satellite constellation using off the shelf components. The aim of this article is to discuss the current trends and technologies towards the feasibility of a space-based aperture array for astronomical observations in the Ultra-Long Wavelength (ULW) regime of greater than 10 m i.e., below 30 MHz. We briefly present the achievable science cases, and discuss the system design for selected scenarios such as extra-galactic surveys. An extensive discussion is presented on various sub-systems of the potential satellite array, such as radio astronomical antenna design, the on-board signal processing, communication architectures and joint space-time estimation of the satellite network. In light of a scalable array and to avert single point of failure, we propose both centralized and distributed solutions for the ULW space-based array. We highlight the benefits of various deployment locations and summarize the technological challenges for future space-based radio arrays.

Horn antennas for generating radio waves bearing orbital angular momentum by using spiral phase plate

Abstract: The design of two new horn antennas for the generation of radio waves bearing orbital angular momentum (OAM) is presented. The OAM mode l = 1 or −1 is generated by combining the guided modes of a circular waveguide with a spiral phase plate. The authors present here two structures to generate OAM wave based on TE11 and TM01 modes. The resulting magnitude and phase patterns of the electrical field and the radiation patterns evidence the presence of waves carrying OAM.

Artificial ionospheric layers driven by high-frequency radiowaves : an assessment

Abstract: High-power ordinary mode radio waves produce artificial ionization in the F-region ionosphere at the European Incoherent Scatter (EISCAT at Tromso, Norway) and High-frequency Active Auroral Research Program (HAARP at Gakona, Alaska, USA) facilities. We have summarized the features of the excited plasma turbulence and descending layers of freshly-ionized (“artificial”) plasma. The concept of an ionizing wavefront created by accelerated suprathermal electrons appears to be in accordance with the data. The strong Langmuir turbulence (SLT) regime is revealed by the specific spectral features of incoherent radar backscatter and stimulated electromagnetic emissions. Theory predicts that the SLT acceleration is facilitated in the presence of photoelectrons. This agrees with the intensified artificial plasma production and the greater speeds of descent but weaker incoherent radar backscatter in the sunlit ionosphere. Numerical investigation of propagation of O-mode waves and the development of SLT and descending layers have been performed. The greater extent of the SLT region at the magnetic zenith than at vertical appears to make magnetic zenith injections more efficient for electron acceleration and descending layers. At high powers, anomalous absorption is suppressed, leading to the Langmuir and upper hybrid processes during the whole heater-on period. The data suggest that parametric UH interactions mitigate anomalous absorption at heating frequencies far from electron gyroharmonics and also generate SLT in the upper hybrid layer. The persistence of artificial plasma at the terminal altitude depends on how close the heating frequency is to the local gyroharmonic.

EMI reduction technology in 85 kHz band 44 kW wireless power transfer system for rapid contactless charging of electric bus

Abstract: A 44 kW wireless power transfer (WPT) system is being developed for rapid contactless charging in an electric bus in the 85 kHz band, the candidate frequency for a wireless charging system for light-duty vehicles that is currently undergoing standardization. For field operation of this WPT system using the 85 kHz band in Japan, permission for use as industrial facilities emitting radio waves is required under the Radio Act. A two-channel WPT system with currents of opposite phase in the two transmit pads of the channels is introduced to reduce radiated emissions to within the Radio Act limits of electromagnetic radiation disturbance by cancelling the emission from each channel. Then, the diagonal placement of the transmit pads for the two channels is proposed to avoid the interference between the two channels where the interference couplings become null. Finally, the measured emission of the 44 kW WPT system in a 10 m anechoic chamber is shown.

Ionospheric signatures of the April 25, 2015 Nepal earthquake and the relative role of compression and advection for Doppler sounding of infrasound in the ionosphere

Abstract: Ionospheric signatures possibly induced by the Nepal earthquake are investigated far outside the epicentral region in Taiwan (~3700 km distance from the epicenter) and in the Czech Republic (~6300 km distance from the epicenter). It is shown that the ionospheric disturbances were caused by long period, ~20 s, infrasound waves that were excited locally by vertical component of the ground surface motion and propagated nearly vertically to the ionosphere. The infrasound waves are heavily damped at the heights of F layer at around 200 km, so their amplitude strongly depends on the altitude of observation. In addition, in the case of continuous Doppler sounding, the value of the Doppler shift depends not only on the advection (up and down motion) of the reflecting layer but also on the compression/rarefaction of the electron gas and hence on the electron density gradient. Consequently, under significant differences of reflection height of sounding radio waves and partly also under large differences in plasma density gradients, the observed ionospheric response at larger distances from the epicenter can be comparable with the ionospheric response observed at shorter distances, although the amplitudes of causative seismic motions differ by more than one order of magnitude.

Could battery-less scatter radio tags achieve 270-meter range?

Abstract: This paper studies whether increased ranges of bistatic scatter radio communication are possible, especially when low-cost, embedded receivers, originally designed for conventional radio (and not for scatter radio) are employed. Wireless power transmission and bistatic scatter radio are closely related, and thus, this work aims to highlight a new exciting, potentially interesting, key-enabling research direction. It is found that for 13 dBm emitter transmission power, 246 meters scatter radio tag-to-reader distance is possible, with packet error rate (PER) less than 1%, while 268 meters are possible at the expense of increased PER, in the order of 10%.

Twisted Radiation by Electrons in Spiral Motion

Abstract: We theoretically show that a single free electron in circular/spiral motion radiates an electromagnetic wave possessing helical phase structure and carrying orbital angular momentum. We experimentally demonstrate it by double-slit diffraction on radiation from relativistic electrons in spiral motion. We show that twisted photons should be created naturally by cyclotron/synchrotron radiations or Compton scatterings in various situations in cosmic space. We propose promising laboratory vortex photon sources in various wavelengths ranging from radio wave to gamma-rays.

Electrodynamics of pulsar magnetospheres

Abstract: We review electrodynamics of rotating magnetized neutron stars, from the early vacuum model to recent numerical experiments with plasma-filled magnetospheres. Significant progress became possible due to the development of global particle-in-cell simulations which capture particle acceleration, emission of high-energy photons, and electron-positron pair creation. The numerical experiments show from first principles how and where electric gaps form, and promise to explain the observed pulsar activity from radio waves to gamma-rays.

Vertical profile of atmospheric conductivity that matches Schumann resonance observations

Abstract: We introduce the vertical profile of atmospheric conductivity in the range from 2 to 98 km. The propagation constant of extremely low frequency (ELF) radio waves was computed for this profile by using the full wave solution. A high correspondence is demonstrated of the data thus obtained to the conventional standard heuristic model of ELF propagation constant derived from the Schumann resonance records performed all over the world. We also suggest the conductivity profiles for the ambient day and ambient night conditions. The full wave solution technique was applied for obtaining the corresponding frequency dependence of propagation constant relevant to these profiles. By using these propagation constants, we computed the power spectra of Schumann resonance in the vertical electric field component for the uniform global distribution of thunderstorms and demonstrate their close similarity in all the models. We also demonstrate a strong correspondence between the wave attenuation rate obtained for these conductivity profiles and the measured ones by using the ELF radio transmissions.

Features of the Electromagnetic and Plasma Disturbances Induced at the Altitudes of the Earth’s Outer Ionosphere by Modification of the Ionospheric F 2 Region Using High-Power Radio Waves Radiated by the SURA Heating Facility

Abstract: In this paper we systematize the results of studying the characteristics of the plasma-density ducts, which was conducted in 2005–2010 during the DEMETER-satellite operation. The ducts are formed at altitudes of about 700 km as a result of the ionospheric F 2 region modification by high-power high-frequency radio waves radiated by the midlatitude SURA heating facility. All the performed measurements are used as the basis for determining the formation conditions for such ducts, the duct characteristics are studied, and the opportunities for the duct influence on the ionosphere–magnetosphere coupling and propagation of radio waves of various frequency ranges are demonstrated. The results of numerical simulation of the formation of such ducts are presented.

Generation of OAM radio beams with modified uniform circular array antenna

Abstract: A modified uniform circular array is analysed and configured to generate radio waves carrying orbital angular momentum (OAM). The relationship between OAM mode and array parameters is derived mathematically. Results show that the produced OAM mode can be altered arbitrarily by changing the exciting frequency when the array is fixed. Moreover, the OAM mode is associated with elevation angle, offering the potential of elevation resolution for radar imaging.

Simulation of orbital angular momentum radio communication systems based on partial aperture sampling receiving scheme

Abstract: The incoherent orbital angular momentum (OAM) radio waves can be used to transmit different information on the same frequency and have a great potential in wireless communication system. However, it needs a large aperture size to receive and demultiplex the orthogonal OAM waves due to the amplitude null in the beam centre and the beam divergence. An improved receiving scheme named partial aperture sampling receiving (PASR) is proposed to solve this problem. The theoretical analysis of PASR is first presented and simulations of OAM radio communication link are carried on to evaluate the performance of PASR. The effects of some non-ideal receiver conditions, e.g. radial deviation and angular deviation on the PASR scheme and the superiority of PASR are explored. These simulated results will give a helpful guide on the manipulation of practical OAM-based wireless communication systems.

A survey on Li-Fi technology

Abstract: In the present era, Wi-Fi is the most trending domain. As internet users almost double every year, there is an enormous load on radio spectrum that leads to congestion. To get better bandwidth, efficiency and speed, a new technology Li-Fi has evolved. Li-Fi stands for Light Fidelity. It is a bidirectional and wireless mode of communication using light. It uses the unused visible spectrum and reduces the load on radio spectrum. Li-Fi can be simply put to be Wi-Fi but instead of radio waves light is used as a medium. Here, data is transmitted using light whose intensity varies faster than human eye to capture. Instead of using modems, Li-Fi uses LED bulbs with transceiver. Data transmission in Li-Fi is about 100 times faster than Wi-Fi. Here, in this paper we explore the need for Li-Fi.

The Electromagnetic Spectrum

Abstract: The first chapter is an introductory chapter. It defines the electromagnetic spectrum and different regions of the spectrum, such as γ -rays, X-rays, UV-Vis, IR, microwave, and radiowave regions. The chapter then discusses the effect of these types of radiation on matter when they fall on it.

Measuring radio emission from cosmic ray air showers with a digital radio telescope

Abstract: The earth is continously bombarded by highly energetic particles, the cosmic radiation. Even 90 years after their discovery the origin and acceleration of the highest energy particles is still unknown. Air showers from cosmic rays are known to emit radio pulses since these pulses were detected in 1965. In the 1970 ties the measurement of these radio pulses ceased almost completely mostly due to difficulties with radio interference, uncertainty about the interpretation of the results and the success of other methods. The measurement of radio pulses from air showers has a number of advantages: It gives a much higher duty cycle than measuring optical light, it is complementary to measuring the particles that reach the ground level, and with radio one can get a good direction estimate for the air shower. The advent of fast digital computers and high bandwidth, high dynamic range ADCs enables us to use digital filtering and beam forming to suppress the radio interference. To test this technology we set up LOPES a prototype digital radio telescope in the scope of this thesis. It consists of 30 single polarisation antennas (10 in the first phase) that are set up at the site of the KASCADE-Grande experiment, an existing air shower array. It directly samples the radio signal in the frequency range from 40 to 80MHz and stores 0.82ms of raw data every time it was triggered by KASCADEGrande. For the analysis the data is offline correlated with data from the KASCADE array, radio interference is digitally filtered, and a beam in the direction given by the KASCADE array is formed. With this we have been able to reliably pick out radio pulses from air showers. The data from the first phase of LOPES are also analysed. By making cuts on the shower size (e.g. on the number of muons measured by KASCADE-Grande) and on the angle to the geomagnetic field one can select events so that each has a detected air shower radio pulse. The height of the radio pulse shows a nearly linear dependence on the shower size (with a power law index slightly smaller than one), an exponential decline with the distance of the antennas to the shower axis, and a monotonic rise with the angle of the air shower to the geomagnetic field. The latter dependence is a discrepancy to the current theoretical predictions. This has to be studied with better theoretical models and further measurements, e.g. of the polarisation characteristics. We have shown that digital radio telescopes can measure radio pulses from air showers and give reproducible results. This is the first step to establish radio measurements of air showers as an additional method of cosmic ray research.

A directional HF noise model: Calibration and validation in the Australian region

Abstract: The performance of systems using HF (high frequency) radio waves, such as over-the-horizon radars, is strongly dependent on the external noise environment. However, this environment has complex behavior and is known to vary with location, time, season, sunspot number, and radio frequency. It is also highly anisotropic, with the directional variation of noise being very important for the design and development of next generation over-the-horizon radar. By combining global maps of lightning occurrence, raytracing propagation, a model background ionosphere and ionospheric absorption, the behavior of noise at HF may be modeled. This article outlines the principles, techniques, and current progress of the model and calibrates it against a 5 year data set of background noise measurements. The calibrated model is then compared with data at a second site.

Cluster Mergers and the Origin of the ARCADE-2 Excess

Abstract: Radio observations at multiple frequencies have detected a significant isotropic emission component between 22 MHz and 10 GHz, commonly termed the ARCADE-2 Excess. The origin of this radio emission is unknown, as the intensity, spectrum and isotropy of the signal are difficult to model with either traditional astrophysical mechanisms or novel physics such as dark matter annihilation. We posit a new model capable of explaining the key components of the excess radio emission. Specifically, we show that the re-acceleration of non-thermal electrons via turbulence in merging galaxy clusters are capable of explaining the intensity, spectrum, and isotropy of the ARCADE-2 data. We examine the parameter spaces of cluster re-acceleration, magnetic field, and merger rate, finding that the radio excess can be reproduced assuming reasonable assumptions for each. Finally, we point out that future observations will definitively confirm or rule-out the contribution of cluster mergers to the isotropic radio background.

Modification of the High-Latitude Ionospheric F Region By High-Power HF Radio Waves at Frequencies Near the fifth and Sixth Electron Gyroharmonics

Abstract: We study the modification effects of the high-latitude ionospheric F region induced by a highpower O-mode HF radio wave injected towards the magnetic zenith, at frequencies near the fifth and sixth electron gyroharmonics using the EISCAT/Heating facility. Multi-instrument diagnostics with the EISCAT incoherent scatter radar (930 MHz) at Tromso, Norway, the CUTLASS coherent radar at Hankasalmi, Finland, and stimulated electromagnetic emission (SEE) receiver at Tromso, has been used for analysis of the observed phenomena. The behavior of the ionospheric plasma parameters (electron’s density and temperature), small-scale artificial field-aligned irregularities, plasma and ion-line spectra, and ionospheric SEE are analyzed in detail. Modification effects near the fifth and sixth electron gyroharmonics have been compared. The coexistence of the thermal (resonance) parametric instability, parametric decay (striction) instability, and/or oscillating two-stream instability was found at these frequencies. The excitation of instabilities occurred at altitudes close to the reflection altitude of the HF pump wave and at the altitudes of the upper-hybrid resonance.