Angular Power Distribution Research Articles

Hysteresis phenomenon in single electron nonlinear Thomson scattering in tightly focused linearly polarized lasers caused by collision position changes

The collision between high-energy electrons and linearly polarized laser pulses is systematically studied, which has significant application value. The effect of different laser parameters on the spectrum and power angular distribution has been analyzed. The maximum transverse amplitude of the electron motion track changes as one moves farther away from the focal point acting as the electronic initial position. Concurrently, an extensive examination of the off-axis properties of the electron is carried out. As the form of scattering changes from linear to nonlinear, the angular radiation of its power distribution exhibits intriguing characteristics. We found the ‘hysteresis’ phenomenon of the radiation characteristics. Our research can serve as a useful resource for comprehending and using laser electron interactions.

The NANOGrav 15 yr Data Set: Search for Anisotropy in the Gravitational-wave Background

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has reported evidence for the presence of an isotropic nanohertz gravitational-wave background (GWB) in its 15 yr data set. However, if the GWB is produced by a population of inspiraling supermassive black hole binary (SMBHB) systems, then the background is predicted to be anisotropic, depending on the distribution of these systems in the local Universe and the statistical properties of the SMBHB population. In this work, we search for anisotropy in the GWB using multiple methods and bases to describe the distribution of the GWB power on the sky. We do not find significant evidence of anisotropy. By modeling the angular power distribution as a sum over spherical harmonics (where the coefficients are not bound to always generate positive power everywhere), we find that the Bayesian 95% upper limit on the level of dipole anisotropy is (C l=1/C l=0) < 27%. This is similar to the upper limit derived under the constraint of positive power everywhere, indicating that the dipole may be close to the data-informed regime. By contrast, the constraints on anisotropy at higher spherical-harmonic multipoles are strongly prior dominated. We also derive conservative estimates on the anisotropy expected from a random distribution of SMBHB systems using astrophysical simulations conditioned on the isotropic GWB inferred in the 15 yr data set and show that this data set has sufficient sensitivity to probe a large fraction of the predicted level of anisotropy. We end by highlighting the opportunities and challenges in searching for anisotropy in pulsar timing array data.

Cyclotron radiation from shaped electron wavefunctions

Recent years have shown increasing interest in understanding the role of the wavefunction of a quantum source on the characteristics of its emitted radiation. In this work, we demonstrate that shaping the wavefunction of the source can drastically change the instantaneous emission. We exemplify this concept by examining an electron in cyclotron motion, calculating the angular power distribution of emission by an electron in a Schrodinger cat state. The emitted cyclotron radiation reveals a breakdown of classical–quantum correspondence. The short-time dynamics of the radiation process shows deviations in the power and electron trajectory that disappear at long times, where the predictions of classical electrodynamics are recovered.

Spatial radiation features of the off-axis collision between a relativistic electron and a tightly focused linearly polarized laser

The collision between relativistic electrons and a tightly focused linearly polarized laser pulse produced nonlinear inverse Thomson scattering (NITS), which generates backward x-rays. The effects of the initial transverse position of electrons with varied initial energy on the angular distribution of radiation power and spectrum are studied through numerical simulation. For the electrons with low initial energy (i.e. ), the off-axis collision breaks the spatial symmetry of x-ray radiation compared with the axial collision, the radiation direction is also torqued towards the same off-axis direction. There exists an optimal initial transverse position of electrons, which means the electron emitted from this position obtains greater radiation power. For the high-energy () electrons, the effect of torsion is not significant. The impact of off-axial is mainly manifested in the high-order harmonic spectrum. These findings help obtain high quality x-rays and modulate NITS radiation symmetry by electron parameters.

Transmission performance of multimode W-type microstructured polymer optical fibers.

By solving the time-independent power flow equation (TI PFE), we study mode coupling in a multimode W-type microstructured polymer optical fiber (mPOF) with a solid-core. The multimode W-type mPOF is created by modifying the cladding layer and reducing the core of a multimode singly clad (SC) mPOF. For such optical fiber, the angular power distributions, the length Lc at which an equilibrium mode distribution (EMD) is achieved, and the length zs for establishing a steady state distribution (SSD) are determined for various arrangements of the inner cladding's air-holes and different launch excitations. This information is useful for the implement of multimode W-type mPOFs in telecommunications and optical fiber sensors.

Time-frequency-dependent directional analysis of room reflections using eigenbeam processing and von Mises-Fisher clustering.

The knowledge of frequency-dependent spatiotemporal features of the reflected soundfield is essential in optimizing the perception quality of spatial audio applications. For this purpose, we need a reliable room acoustic analyzer that can conceive the spatial variations in a decaying reflected soundfield according to the frequency-dependent surface properties and source directivity. This paper introduces a time-frequency-dependent angular reflection power distribution model represented by a von Mises-Fisher (vMF) mixture function to facilitate manifold analysis of a reverberant soundfield. The proposed approach utilizes the spatial correlation of higher-order eigenbeams to deduce the directional reflection power vectors, which are then synthesized into a vMF mixture model. The experimental study demonstrates the directional power variations of early reflections and late reverberations across different frequencies. This work also introduces a measure called the directivity time-span to quantify the duration of anisotropic reflections before it decays into a totally diffused field. We validate the subband performance by comparing it with the eigenbeam multiple signal classification method. The results prove the influence of source position, source directivity, and room environment in the distribution of reflection power, whereas the directivity time-span behaves independent of the source positions.

Measurement of Aspect Angle of Field-Aligned Plasma Irregularities in Mid-Latitude E Region Using VHF Atmospheric Radar Imaging and Interferometry Techniques

Multireceiver and multifrequency radar imaging were carried out with the 46.5 MHz MU radar in Japan (34.85°N and 136.10°E) to examine the aspect sensitivity of field-aligned plasma irregularities (FAIs) in the mid-latitude ionosphere E region. A radar beam was directed to geographic north and at 51° zenith angle, which was normal to the geomagnetic field line around 100 km height. Nineteen receivers and five carrier frequencies were used for radar imaging to retrieve the power distribution in the radar volume, and then the aspect angle along the geomagnetic field line was calculated according to the angular power distribution. Retrieval algorithms such as Fourier, Capon, and norm-constrained Capon (NC-Capon) were employed, in which the NC-Capon was applied to FAIs for the first time and found to be more suitable for the present study. The aspect angles estimated by the NC-Capon ranged between 0.1° and 0.4° mostly, and averaged around 0.2°, which were the same order to the previous measurements with radar interferometry (RI), made for equatorial electrojet irregularities and the lower mid-latitude sporadic E region. For comparison, RI-estimated aspect angles were also investigated and found to be close to that of NC-Capon, but distributed over a wider extent of angles.

Investigation of performance properties of plastic optical fibres used in a traffic light system

We investigate the performance properties of a multimode plastic optical fibre (POF) used in a traffic light system. An analytical function is proposed for predicting the angular power distribution at the output end of a multimode optical fibre when the beam at the input end of the fibre is centrally launched along the fibre axis. We demonstrate how mode coupling affects the output angular power distribution along the fibre and, therefore, the performance of optical fibre used as part of a traffic light system. It is found that as the length of the POF increases, the angular power distribution broadens until it reaches a length at which a steady-state distribution (SSD) is achieved. This broadening is insignificant at short POF lengths of up to 10 m. As a result, the effective radiation area at the output end of any long POF as part of different light systems, such as traffic, building, and bridge light systems, can be determined.

Modeling of Downlink Interference in Massive MIMO 5G Macro-Cell.

Multi-beam antenna systems are the basic technology used in developing fifth-generation (5G) mobile communication systems. In practical implementations of 5G networks, different approaches are used to enable a massive multiple-input-multiple-output (mMIMO) technique, including a grid of beams, zero-forcing, or eigen-based beamforming. All of these methods aim to ensure sufficient angular separation between multiple beams that serve different users. Therefore, ensuring the accurate performance evaluation of a realistic 5G network is essential. It is particularly crucial from the perspective of mMIMO implementation feasibility in given radio channel conditions at the stage of network planning and optimization before commercial deployment begins. This paper presents a novel approach to assessing the impact of a multi-beam antenna system on an intra-cell interference level in a downlink, which is important for the accurate modeling and efficient usage of mMIMO in 5G cells. The presented analysis is based on geometric channel models that allow the trajectories of propagation paths to be mapped and, as a result, the angular power distribution of received signals. A multi-elliptical propagation model (MPM) is used and compared with simulation results obtained for a statistical channel model developed by the 3rd Generation Partnership Project (3GPP). Transmission characteristics of propagation environments such as power delay profile and antenna beam patterns define the geometric structure of the MPM. These characteristics were adopted based on the 3GPP standard. The obtained results show the possibility of using the presented novel MPM-based approach to model the required minimum separation angle between co-channel beams under line-of-sight (LOS) and non-LOS conditions, which allows mMIMO performance in 5G cells to be assessed. This statement is justified because for 80% of simulated samples of intra-cell signal-to-interference ratio (SIR), the difference between results obtained by the MPM and commonly used 3GPP channel model was within 2 dB or less for LOS conditions. Additionally, the MPM only needs a single instance of simulation, whereas the 3GPP channel model requires a time-consuming and computational power-consuming Monte Carlo simulation method. Simulation results of intra-cell SIR obtained this way by the MPM approach can be the basis for spectral efficiency maximization in mMIMO cells in 5G systems.

From bright binaries to bumpy backgrounds: Mapping realistic gravitational wave skies with pulsar-timing arrays

Within the next several years, pulsar-timing array programs will likely usher in the next era of gravitational-wave astronomy through the detection of a stochastic background of nanohertz-frequency gravitational waves, originating from a cosmological population of inspiraling supermassive binary black holes. While the source positions will likely be isotropic to a good approximation, the gravitational-wave angular power distribution will be anisotropic, with the most massive and/or nearby binaries producing signals that may resound above the background. We study such a realistic angular power distribution, developing fast and accurate sky-mapping strategies to localize pixels and extended regions of excess power while simultaneously modeling the background signal from the less massive and more distant ensemble. We find that power anisotropy will be challenging to discriminate from isotropy for realistic gravitational-wave skies, requiring SNR $>10$ in order to favor anisotropy with $10:1$ posterior odds in our case study. Amongst our techniques, modeling the population signal with multiple point sources in addition to an isotropic background provides the most physically-motivated and easily interpreted maps, while spherical-harmonic modeling of the square-root power distribution, $P(\hat\Omega)^{1/2}$, performs best in discriminating from overall isotropy. Our techniques are modular and easily incorporated into existing pulsar-timing array analysis pipelines.

Correlation of Hybrid Beamforming Arrays in the Context of OTA Testing

Hybrid beamforming antenna arrays are a prominent component in communications at millimeter-wave frequencies. Multiple analog beamforming arrays will be used for spatial multiplexing of signals also in hand-held devices. In this letter, we derive the correlation coefficient for signals received by two ideal arrays in simple power angular distribution schemes. The purpose is to develop tools for evaluating over-the-air (OTA) setups for testing of hybrid beamforming devices. We show a few exemplary correlation error evaluations that compare near-field multiprobe OTA setups with a perfect target channel model. Results indicate that the correlation error increases with decreasing range length and channel angular spread. Moreover, larger interarray spacing and subarray sizes increase the correlation error.

Simulation of a new architecture of organic white-light-emitting diode by quantum dot and photonic crystal to improve efficiency

A novel inverted hybrid quantum dot/organic light-emitting diode (IH-QDOLED) with a transparent conducting oxide photonic crystal structure is proposed in this study. Such improved electrical and optical characteristics as luminescence efficiency, extraction efficiency, external quantum efficiency, carrier injection, size-tunable color of QDs, and solution-processable fabrication make IH-QDOLEDs a good candidate with which to achieve high-performance and low-cost LED (light-emitting diode) devices. These efficient LEDs consist of three rows of CdSe quantum dots with different sizes blended in TPBi. In order to optimize the IH-QDOLED structure, we have performed a simulation based on the finite difference time domain (FDTD) method. Also, the characteristics of this novel structure have been compared with those of a conventional structure. As it is found, the maximum external quantum efficiency (EQE) is increased from 30 % to 50 %, and the turn-on voltage has risen from 4.5 V to 5.5 V, compared to the conventional structure. Our results show that the angular distribution of the radiant power is uniform over a wider range of view angles, which can be attributed to the interaction of guided modes with an embedded photonic crystal structure.

81 supra-THz beams generated by a Fourier grating and a quantum cascade laser.

Large heterodyne receiver arrays (~100 pixel) allow astronomical instrumentations to map more area within limited space mission lifetime. One challenge is to generate multiple local oscillator (LO) beams. Here, we succeeded in generating 81 beams at 3.86 THz by combining a reflective, metallic Fourier grating with an unidirectional antenna coupled 3rd-order distributed feedback (DFB) quantum cascade laser (QCL). We have measured the diffracted 81 beams by scanning a single pyroelectric detector at a plane, which is in the far field for the diffraction beams. The measured output beam pattern agrees well with a simulated result from COMSOL Multiphysics, with respect to the angular distribution and power distribution among the 81 beams. We also derived the diffraction efficiency to be 94 ± 3%, which is very close to what was simulated for a manufactured Fourier grating (97%). For an array of equal superconducting hot electron bolometer mixers, 64 out of 81 beams can pump the HEB mixers with similar power, resulting in receiver sensitivities within 10%. Such a combination of a Fourier grating and a QCL can create an LO with 100 beams or more, enabling a new generation of large heterodyne arrays for astronomical instrumentation.

Turbulent power distribution in the local interstellar medium

Context. The interstellar medium (ISM) on all scales is full of structures that can be used as tracers of processes that feed turbulence. Aims. We used H I survey data to derive global properties of the angular power distribution of the local ISM. Methods. HI4PI observations on an nside = 1024 HEALPix grid and Gaussian components representing three phases, the cold, warm, and unstable lukewarm neutral medium (CNM, WNM, and LNM), were used for velocities |vLSR|≤ 25 km s−1. For high latitudes |b| &gt; 20° we generated apodized maps. After beam deconvolution we fitted angular power spectra. Results. Power spectra for observed column densities are exceptionally well defined and straight in log-log presentation with 3D power law indices γ ≥−3 for the local gas. For intermediate velocity clouds (IVCs) we derive γ = −2.6 and for high velocity clouds (HVCs) γ = −2.0. Single-phase power distributions for the CNM, LNM, and WNM are highly correlated and shallow with γ ~−2.5 for multipoles l ≤ 100. Excess power from cold filamentary structures is observed at larger multipoles. The steepest single-channel power spectra for the CNM are found at velocities with large CNM and low WNM phase fractions. Conclusions. The phase space distribution in the local ISM is configured by phase transitions and needs to be described with three distinct different phases, being highly correlated but having distributions with different properties. Phase transitions cause locally hierarchical structures in phase space. The CNM is structured on small scales and is restricted in position-velocity space. The LNM as an interface to the WNM envelops the CNM. It extends to larger scales than the CNM and covers a wider range of velocities. Correlations between the phases are self-similar in velocity.

Characterization of a Y-Coupler and Its Impact on the Performance of Plastic Optical Fiber Links

Couplers and splitters are common devices in single-mode and multi-mode glass fibers applications, where they perform a variety of functions. However, when switching to plastic optical fibers (POFs), there is a shortage of commercial devices, which are usually custom-made. The problem with these devices is that modal power distribution in POFs is easily modified by spatial disturbances that produce a localized strong power transfer between modes, thus changing their transmission properties. In this work, a commercial Y-coupler designed for POFs is experimentally characterized. Measurements of its spectral, spatial and temporal characteristics have been performed, including insertion loss as a function of wavelength, angular power distribution, and frequency response. The obtained results show that this device has an equalizing effect over the power spatial distribution that reduces the fiber bandwidth, demonstrating the importance of considering the impact of this type of devices on the transmission properties of any POF system.

Empirical Modeling of Radiowave Angular Power Distributions in Different Propagation Environments at 60 GHz for 5G

The design of 5th generation (5G) wireless systems requires the description and modeling of the radio channel where communication will take place. As 5G will employ massive multiple input–multiple output (MIMO) to cope with the high data rates, the channel models should include the description of radiowave angular power distribution (APD) around the terminals. In this paper, we present the results of a measurement campaign of these APDs in four different environments and provide their main parameters. This will facilitate the incorporation of these results into current 5G channel models. We also analyze the maximum received power improvement that could be achieved by combining the power reaching the terminal from different angles and provide the improvement values for the four scenarios. The research was conducted at 60 GHz, one of the frequency bands proposed for 5G systems.

Two-Dimensional DOA Estimation for Incoherently Distributed Sources with Uniform Rectangular Arrays.

Aiming at the two-dimensional (2D) incoherently distributed (ID) sources, we explore a direction-of-arrival (DOA) estimation algorithm based on uniform rectangular arrays (URA). By means of Taylor series expansion of steering vector, rotational invariance relations with regard to nominal azimuth and nominal elevation between subarrays are deduced under the assumption of small angular spreads and small sensors distance firstly; then received signal vectors can be described by generalized steering matrices and generalized signal vectors; thus, an estimation of signal parameters via rotational invariance techniques (ESPRIT) like algorithm is proposed to estimate nominal elevation and nominal azimuth respectively using covariance matrices of constructed subarrays. Angle matching method is proposed by virtue of Capon principle lastly. The proposed method can estimate multiple 2D ID sources without spectral searching and without information of angular power distribution function of sources. Investigating different SNR, sources with different angular power density functions, sources in boundary region, distance between sensors and number of sources, simulations are conducted to investigate the effectiveness of the proposed method.

New method for calculating the coupling coefficient in graded index optical fibers

A simple method is proposed for determining the mode coupling coefficient D in graded index multimode optical fibers. It only requires observation of the output modal power distribution P(m, z) for one fiber length z as the Gaussian launching modal power distribution changes, with the Gaussian input light distribution centered along the graded index optical fiber axis (θ0=0) without radial offset (r0 = 0). A similar method we previously proposed for calculating the coupling coefficient D in a step-index multimode optical fibers where the output angular power distributions P(θ, z) for one fiber length z with the Gaussian input light distribution launched centrally along the step-index optical fiber axis (θ0=0) is needed to be known.

Microcellular Radio Channel Characterization at 60 GHz for 5G Communications

The 60-GHz frequency band is one of the candidates for 5G communications. However, there are not many results that report the radio channel characteristics at outdoor environments for large channel bandwidths using directive steering antennas at the mobile end. We present the results of a wideband measurement campaign using directional steering antennas at the mobile end, an RF frequency bandwidth of 1 GHz, and propagation distances of up to 405 m. We propose to describe the angular power distribution using Gaussian functions. The parameters for the model are empirically determined from the measurements.

Attenuation and diffusion produced by small-radius curvatures in POFs.

Our aim is to characterize curvatures using a methodology previously applied to other localized disturbances in plastic optical fibers (POFs). The effects of several curvature radii and turn angles have been analyzed, so that for each condition, angular dependent attenuation and diffusion are obtained from experimental measurements to construct a matrix that accounts for the global effects of power loss and mode mixing introduced by the curvature over the angular power distribution. Power loss as a function of bend radius was calculated using the characteristic matrices and compared to experimental results to validate the model. This curvature model can be a useful tool to predict the impact of bends on transmission properties as is demonstrated in the example of a small network in a domestic environment.