scholarly journals Ray tracing with multi-radiation transmitters

2012 ◽  
Vol 10 ◽  
pp. 75-78
Author(s):  
R. Brem ◽  
T. F. Eibert
Keyword(s):  
Integral Equation ◽  
Ray Tracing ◽  
Field Condition ◽  
Fast Multipole Method ◽  
Near Field ◽  
Far Field ◽  
Field Region ◽  
Equation Solving ◽  
Close Proximity ◽  
Modeling Accuracy

Abstract. A restriction in using electromagnetic ray tracing for field prediction is given by the far-field condition: the results are only valid in the far-field region of the radiator. In this paper, it will be shown how ray tracing for accurate field computation can also be applied in the near-field regions of transmitters. The reduction of required large distances between transmitter and receiver is achieved by subdividing the transmitter in smaller subtransmitters. Even for complex transmitters, e.g. antennas with objects in close proximity such as metallic carrier platforms, subtransmitter models can be very efficiently generated by using the Multilevel Fast Multipole Method (MLFMM). This well-known integral equation solving technique makes very large problems in computational electromagnetics manageable. The subtransmitters can be directly generated based on this algorithm. A simulation example will show the improved modeling accuracy and options for simplification and refinement will also be discussed.

scholarly journals Experimental observation of asymmetrical microwave jets and far-field distribution generated by a dual-material system

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
B. Varghese ◽  
O. Shramkova ◽  
P. Minard ◽  
L. Blondé ◽  
V. Drazic ◽  
...  
Keyword(s):  
Near Field ◽  
Microwave Frequency ◽  
Far Field ◽  
Material System ◽  
Field Region ◽  
Edge Diffraction ◽  
Jet Behavior ◽  
Electric Field Profile ◽  
Dual Material ◽  
Plane Wave Diffraction

AbstractIn this paper, we report the experimental and numerical investigation of plane wave diffraction by an all-dielectric dual-material cuboid. Edge diffraction by a cuboid leads to the generation of a narrow, high intensity beam in the near-field region called a photonic jet. We examine the dependence of the jet behavior and orientation on the materials and dimensions of constitutive parts in the microwave frequency domain. The possibility to shift and deviate the resultant microwave jet in the near-field region of such a structure depending on the size of constitutive parts is demonstrated numerically. Experimentally, we observe a shift in the spatial position of the jet. The experimental asymmetric electric field profile observed in the far-field region is attributed to the input of multiple edge waves generated by the dual-material cuboid. The presented results may be scaled at different frequency bands such as optical frequencies for designing nanostructures enabling the focusing and deviation functionality and creation of new optical devices which would satisfy the needs of emerging nanophotonic applications.

scholarly journals Method to Determine the Far-Field Beam Pattern of A Long Array From Subarray Beam Pattern Measurements

Sensors ◽  
2020 ◽  
Vol 20 (4) ◽  
pp. 1236
Author(s):  
Donghwan Jung ◽  
Jeasoo Kim
Keyword(s):  
Conventional Method ◽  
Field Condition ◽  
Near Field ◽  
Plane Waves ◽  
Measurement Data ◽  
Beam Pattern ◽  
Far Field ◽  
Water Tank ◽  
Discrete Line ◽  
Line Array

Beam pattern measurement is essential to verifying the performance of an array sonar. However, common problems in beam pattern measurement of arrays include constraints on achieving the far-field condition and reaching plane waves mainly due to limited measurement space as in acoustic water tank. For this purpose, the conventional method of measuring beam patterns in limited spaces, which transform near-field measurement data into far-field results, is used. However, the conventional method is time-consuming because of the dense spatial sampling. Hence, we devised a method to measure the beam pattern of a discrete line array in limited space based on the subarray method. In this method, a discrete line array with a measurement space that does not satisfy the far-field condition is divided into several subarrays, and the beam pattern of the line array can then be determined from the subarray measurements by the spatial convolution that is equivalent to the multiplication of beam pattern. The proposed method was verified through simulation and experimental measurement on a line array with 256 elements of 16 subarrays.

scholarly journals Bessel-like light beams formed by the two-component scheme consisting of an axicon and a spherical lens

2020 ◽  
Vol 56 (3) ◽  
pp. 373-383
Author(s):  
N. A. Khilo ◽  
P. I. Ropot ◽  
P. K. Petrov ◽  
V. N. Belyi
Keyword(s):  
Light Field ◽  
Near Field ◽  
Cone Angle ◽  
Longitudinal Component ◽  
Optical Scheme ◽  
Far Field ◽  
Field Region ◽  
Spherical Lens ◽  
Bessel Beams ◽  
Remote Probing

The combination in an optical scheme of rather different elements such as axicons and spherical lenses allows forming light fields that differ by a variety of properties. The simplest example of such a scheme consists of an axicon and a spherical lens spatially separated from it. Though this scheme was investigated earlier, the region of so-called secondary focusing located behind the well-known annular focus has not been studied yet. In this paper, the analytical and numerical analysis of a light field in the region of secondary focusing is conducted. The boundaries of this region are determined, and the longitudinal and transverse distribution of the light intensity is calculated. It is shown that the near field region of secondary focusing is formed in the regime of abrupt autofocusing of the annular field. It is established that in a general case the transverse intensity distribution in the far field region is a superposition of an annular field and an oscillating axialtype field. The distance between the axicon and the lens is determined when the annular component of the field practically disappears. It is shown that in this case the light field in the region of the secondary focusing is a locally Bessel light beam. The peculiarity of this beam is that its cone angle depends on the longitudinal component, namely, decreases in inverse proportion while the distance z increases. The important feature of such z-dependent Bessel beams is the absence of their transformation into annular fields, as it occurs for ordinary Bessel or Bessel-Gaussian beams in the far field region. This opens the prospect for application of z-dependent Bessel beams for optical communication in free space and remote probing, which is why such beams are perspective for application in different systems of remote probing.

scholarly journals Efficient Compression of Far Field Matrices in Multipole Algorithms based on Spherical Harmonics and Radiating Modes

2012 ◽  
Vol 1 (2) ◽  
pp. 5
Author(s):  
A. Schroeder ◽  
H.-D. Bruens ◽  
C. Schuster
Keyword(s):  
Spherical Harmonics ◽  
Electromagnetic Scattering ◽  
Spherical Harmonic ◽  
Fast Multipole Method ◽  
Near Field ◽  
Surface Current ◽  
Far Field ◽  
Radiation Patterns ◽  
Electromagnetic Problems ◽  
Harmonic Representation

This paper proposes a compression of far field matrices in the fast multipole method and its multilevel extension for electromagnetic problems. The compression is based on a spherical harmonic representation of radiation patterns in conjunction with a radiating mode expression of the surface current. The method is applied to study near field effects and the far field of an antenna placed on a ship surface. Furthermore, the electromagnetic scattering of an electrically large plate is investigated. It is demonstrated, that the proposed technique leads to a significant memory saving, making multipole algorithms even more efficient without compromising the accuracy.

Turbulence anisotropy with higher-order moments in flow through passive grid under rigid boundary influence

2020 ◽  
pp. 095440622096973
Author(s):  
Pankaj Kumar Raushan ◽  
Santosh Kumar Singh ◽  
Koustuv Debnath
Keyword(s):  
Reynolds Stress ◽  
Isotropic Turbulence ◽  
Near Field ◽  
Far Field ◽  
Field Region ◽  
Rigid Boundary ◽  
Third Order ◽  
Solidity Ratio ◽  
Eigen Values ◽  
Flow Through

The investigation presents the estimate of the degree of deviation from the isotropic turbulence in terms of Reynolds stress tensor for grid generated turbulence under the influence of bottom boundary. The turbulence triangle, Eigen values, and the invariant functions are presented at near and far field regions of the grids with different solidity ratio. In addition, the work also deals with the analysis based on third-order moments of the velocity fluctuations and the ratio of momentum flux to the turbulent kinetic energy in the frequency domain. The Reynolds stress anisotropy exposes that the anisotropic invariant maps possess a closed looping trend in the near field region and an open looping trend in the far-field region of the grid. Further, to describe the physical behaviour of the velocity time-series of random fluctuating components in the stream-wise directions, the probability distribution function are estimated and interpreted.

scholarly journals Near-Field to Far-Field RCS Prediction on Arbitrary Scanning Surfaces Based on Spherical Wave Expansion

Sensors ◽  
2020 ◽  
Vol 20 (24) ◽  
pp. 7199
Author(s):  
Woobin Kim ◽  
Hyeong-Rae Im ◽  
Yeong-Hoon Noh ◽  
Ic-Pyo Hong ◽  
Hyun-Sung Tae ◽  
...  
Keyword(s):  
Near Field ◽  
Linear Equations ◽  
Spherical Wave ◽  
Scattered Wave ◽  
Far Field ◽  
Field Region ◽  
System Of Linear Equations ◽  
Wave Expansion ◽  
Field Transformation ◽  
Spherical Wave Expansion

Near-field to far-field transformation (NFFFT) is a frequently-used method in antenna and radar cross section (RCS) measurements for various applications. For weapon systems, most measurements are captured in the near-field area in an anechoic chamber, considering the security requirements for the design process and high spatial costs of far-field measurements. As the theoretical RCS value is the power ratio of the scattered wave to the incident wave in the far-field region, a scattered wave measured in the near-field region needs to be converted into field values in the far-field region. Therefore, this paper proposes a near-field to far-field transformation algorithm based on spherical wave expansion for application in near-field RCS measurement systems. If the distance and angular coordinates of each measurement point are known, the spherical wave functions in an orthogonal relationship can be calculated. If each weight is assumed to be unknown, a system of linear equations as numerous as the number of samples measured in the near electric field can be generated. In this system of linear equations, each weight value can be calculated using the iterative least squares QR-factorization method. Based on this theory, the validity of the proposed NFFFT is verified for several scatterer types, frequencies and measurement distances.

scholarly journals Planar scanning measurement of monostatic/bistatic RCS by near-field far-field transformation based on fast multipole method

2015 ◽  
Vol 4 (9) ◽  
pp. 282-286
Author(s):  
Shuntaro Omi ◽  
Toru Uno ◽  
Takuji Arima ◽  
Yujiro Kushiyama ◽  
Takao Fujii
Keyword(s):  
Fast Multipole Method ◽  
Near Field ◽  
Far Field ◽  
Fast Multipole ◽  
Field Transformation ◽  
Multipole Method
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