共查询到20条相似文献,搜索用时 718 毫秒
1.
Y. Yan 《International Journal of Infrared and Millimeter Waves》2001,22(2):361-371
As the operating frequencies of communication systems more higher into the millimeter wave range, and the density of particles in medium is more denser, the effects of multiple scattering in sandstorm become more significant. This paper treats the problems of electromagnetic multiple scattering in strong sandstorm by the Monte Carlo method. Based on the analytical theory of multiple scattering, the millimeter wave propagation and scattering in discrete random media are investigated by means of the particle-tracking technique. The millimeter wave is regarded as a Markov chain of wave particle collisions in a medium in which it is scattered and absorbed. Considering the effect of multiple scattering, millimeter wave attenuation induced by strong sandstorm is simulated numerically. The values of theoretical calculation are in good agreement with the measured results of simulated experiment at 34 and 93 GHz. 相似文献
2.
A. Maitra Marina Dan A. K. Sen K. Bhattacharyya C. K. Sarkar 《International Journal of Infrared and Millimeter Waves》1993,14(3):703-713
Distortion of pulses with pulse widths ranging from 0.1 to 1 ns propagating with carrier frequencies in the range 10–100 GHz through rain filled medium has been estimated considering the absorptive and dispersive effects produced by rain drops on the propagation of millimeter waves. It is found that the rain induced broadening or compression can be quite appreciable for very short pulses in the window region of millimeter wave band under intense and extensive raining conditions. 相似文献
3.
Hansen R Måsøy SE Tangen TA Angelsen BA 《The Journal of the Acoustical Society of America》2011,129(2):1117-1127
A method of acoustic imaging is discussed that potentially can improve the diagnostic capabilities of medical ultrasound. The method, given the name second order ultrasound field imaging, is achieved by the processing of the received signals from transmitted dual frequency band pulse complexes with at least partly overlapping high frequency (HF) and low frequency (LF) pulses. The transmitted HF pulses are used for image reconstruction whereas the transmitted LF pulses are used to manipulate the elastic properties of the medium observed by the HF imaging pulses. In the present paper, nonlinear propagation effects observed by a HF imaging pulse due to the presence of a LF manipulation pulse is discussed. When using dual frequency band transmit pulse complexes with a large separation in center frequency (e.g., 1:10), these nonlinear propagation effects are manifested as a nonlinear HF propagation delay and a HF pulse distortion different from conventional harmonic distortion. In addition, with different transmit foci for the HF and LF pulses, nonlinear aberration will occur. 相似文献
4.
The propagation property of an electromagnetic wave in with the finite-difference time-domain method. The effects a thin plasma layer at high pressure is investigated of the non-uniformity of plasma distribution, and the frequency of incident wave on the propagation property of the electromagnetic wave are discussed. Numerical results indicate that the phase shift and the reflectivity of wave are sensitive to plasma density distribution, and reflectivity is lower at the middle band of frequency for different plasma distributions. 相似文献
5.
Yanyu Wei Wenxiang Wang Yubin Gong Shenggang Liu 《International Journal of Infrared and Millimeter Waves》2001,22(5):737-756
A dielectric-loaded, ridged helical groove slow-wave structure for the millimeter wave traveling wave tube is presented in this paper. The effects of the groove depth, ridge dimensions and the dielectric permitivety on the wave propagating properties and the interaction impedance are investigated in detail. From the analysis, it is indicated that for broader band amplification in a helical groove travelling wave tube, a ridged helical structure with shallow groove and loaded by dielectric with proper relative permitivety may be applied. 相似文献
6.
Phani AS Woodhouse J Fleck NA 《The Journal of the Acoustical Society of America》2006,119(4):1995-2005
Plane wave propagation in infinite two-dimensional periodic lattices is investigated using Floquet-Bloch principles. Frequency bandgaps and spatial filtering phenomena are examined in four representative planar lattice topologies: hexagonal honeycomb, Kagomé lattice, triangular honeycomb, and the square honeycomb. These topologies exhibit dramatic differences in their long-wavelength deformation properties. Long-wavelength asymptotes to the dispersion curves based on homogenization theory are in good agreement with the numerical results for each of the four lattices. The slenderness ratio of the constituent beams of the lattice (or relative density) has a significant influence on the band structure. The techniques developed in this work can be used to design lattices with a desired band structure. The observed spatial filtering effects due to anisotropy at high frequencies (short wavelengths) of wave propagation are consistent with the lattice symmetries. 相似文献
7.
This paper analyzes the propagation characteristics of the millimeter wave in various circular section tunnels. The received
power, path loss and delay spread are discussed in detail using the verified software of Wireless InSite. The investigated
tunnel models with circular section include the long straight tunnel, the tunnel with train inside and the curved tunnels
with different curvature. The simulated results are verified by the experimental value in the actual tunnel. Several valuable
conclusions are obtained, which would offer theoretical and practical references for the millimeter wave communication in
limited spaces. 相似文献
8.
T Utsunomiya M. Sekine 《International Journal of Infrared and Millimeter Waves》2005,26(11):1651-1660
We have conducted a millimeter wave propagation experiment at 103 GHz (2.9 mm) on a propagation path of 390 m. The results
were compared with the rain attenuation calculations from the Marshall-Palmer, Best, Joss-Thomas-Waldvogel and Weibull distributions
for raindrop-size. It has been shown that the Weibull distribution has a good agreement with the experiments. 相似文献
9.
Y. Yan 《International Journal of Infrared and Millimeter Waves》2003,24(9):1525-1530
The earth's atmosphere plays an important role in microwave remote sensing and millimeter wave propagation. In this paper, we study the measurements of the attenuation due to atmospheric gases have been made in China, put forward a empirical model for the atmospheric attenuation of millimeter wave in China area. 相似文献
10.
Liquid water fade margin requirements for infrared and millimeter wave runway imaging sensors in fog
Robert E. Marshall David A. de Wolf Christos Kontogeorgakis 《International Journal of Infrared and Millimeter Waves》1997,18(6):1133-1149
Liquid water content and particle size distribution at each ten meters in the vertical for a deep advection fog and a shallow
radiation fog are analyzed to determine the liquid water loss at millimeter and infrared wavelengths. The liquid water fade
margin is calculated along a three degree glideslope in each fog from the current height above the runway to the touchdown
point. Millimeter wave fade margin requirements are calculated from the vertical distribution of bulk liquid water content
and infrared fade margin requirements are predicted from the vertical distribution of dropsize. Fog dropsize distributions
for both fog layers are well fitted to a gamma distribution with a median drop diameter of approximately 9 microns. Millimeter
wave imaging sensors operating in a shallow radiation fog are shown to require less than 1 dB of one-way liquid water fade
margin. In the deep advection fog, one-way liquid water fade margin requirements at 8.6 mm, 6.8 mm, and 3.2 mm are predicted
to be 1, 2, and 6.7 dB respectively. In comparison, the one-way liquid water fade margin requirements at near, middle, and
far infrared wavelengths are two orders of magnitude greater than at millimeter wavelengths and indicate the fog layers are
opaque to infrared imaging sensors even near the touchdown point. The specific attenuations predicted in the two fogs are
consistent with previously reported values. 相似文献
11.
Shunkang Liu 《International Journal of Infrared and Millimeter Waves》2000,21(5):745-750
In millimeter wave band, interaction impedance and efficiency of the ring-bar circuit are higher than helix. Ring-bar traveling wave tubes (TWTs) do not easy yield backward wave oscillation at high operating voltages. Thus ring-bar TWTs can reach higher power lever. On basic of computation of dispersion and interaction impedance, a fast estimation models of RF parameters for MMW ring-bar TWTs are given in this paper. It is available in designing tube to reduce developing period. 相似文献
12.
Haiyan Chen Jizhi Dai Yongzhi Liu 《International Journal of Infrared and Millimeter Waves》2004,25(5):749-757
The effect of fog and clouds in millimeter communication is discussed, and the attenuation caused by fog and clouds is reviewed. Signal-to-noise ratio (SNR) of image is derived using relating models of fog and clouds attenuation. According to the relation of image quality and its signal-to-noise ratio, the system behavior is forecasted theoretically. It is shown that the signal-to-noise ratio of receiver at certain transmitter power is inverse with radio wave frequency, from about 70dB at 10GHz to 48dB for fog and 49dB for clouds. The image quality of received signal at certain transmitter power is inverse with radio wave frequency, from about 7 grade at 10GHz to 5.27 grade for fog and 5.37 grade for clouds. The above calculated results are consistent with experimental results. 相似文献
13.
《International Journal of Infrared and Millimeter Waves》2007,28(10):821-829
This work presents a fullwave analysis for annular ring microstrip antennas on uniaxial anisotropic substrates. The effect
of the anisotropic substrates on the antenna performance at the millimeter wave band is investigated. The analysis is performed
in the Hankel transform domain using Hertz vector potentials and Galerkin Method. Numerical results are presented for the
antenna main characteristics such as resonant frequency and radiation pattern. 相似文献
14.
Th. Fickenscher 《International Journal of Infrared and Millimeter Waves》2004,25(3):553-567
Recently, Laser-controlled four-port beam-splitter-type couplers with photoinduced plasma layer and band-limited coupling characteristics at millimeter wave frequencies have been proposed for use in dielectric and image guides and circuits. In order to achieve a large dynamic range regarding the optical control of the coupling coefficient narrowband destructive interference in the dark state has been used. In this paper an ultra-broadband coupler for applications at millimeter wave band is proposed. This configuration requires waveguides to be transparent for the optical excitation. Numerical examples for the lowest order modes are presented and discussed considering fused quartz for the dielectric strips of the guides and a 50 m GaAs film for the active layer. 相似文献
15.
R. S. Chen X. W. Ping K. F. Tsang 《International Journal of Infrared and Millimeter Waves》2003,24(12):2139-2151
The Incomplete Cholesky factorizations preconditioning scheme is applied to the conjugate gradient (CG) method for solving a large system of linear equations resulting from finite element method (FEM) analysis of millimeter wave filters. As is well known, the convergence of CG method deteriorates with increasing EM wave number and in millimeter wave band the eigen-values of A are more and more scattered between both the right and the left half-plane. The efficient implementation of this preconditioned CG (PCG) algorithm is described in details for Complex coefficient matrix. With incomplete factorization preconditioning scheme in the conjugate gradient algorithm, this PCG approach can reach convergence in 20 times CPU time shorter than CG for several typical millimeter wave structures. 相似文献
16.
S. I. Tarapov F. Yldz Yu. A. Tuchkin 《International Journal of Infrared and Millimeter Waves》2002,23(5):745-754
Electrodynamical features of rectangular cavity resonators as experimental cells of Electron Spin Resonance spectrometer for the millimeter frequency band have been investigated. Measurements and analytical estimations of features of three types of resonators (film-wall type, diffraction grating-wall type, double-wall type) are presented. The advantages and imperfections of each design as well as recommendations for their applications in millimeter wave magnetospectroscopy are given. 相似文献
17.
Xiong Lizhi Qi Lanfen Zhu Huabin 《International Journal of Infrared and Millimeter Waves》2003,24(12):2095-2104
The following paper introduces a smart antenna system with MUSIC algorithm for indoor millimeter wave communication. The smart antenna system separates main transmission paths towards receiver by antenna array. Maximal-ratio combination (MRC) of the separated transmission paths provides nearly optimal performance of receiver. Multipath distortion and noise can be greatly reduced by the system. 相似文献
18.
S. Mitsudo Aripin T. Shirai T. Matsuda T. Kanemaki T. Idehara 《International Journal of Infrared and Millimeter Waves》2000,21(4):661-676
ESR device using a submillimeter wave gyrotron as a radiation source and a pulse magnet for high field up to 30 T has been constructed. Our gyrotrons (Gyrotron FU series) were developed as millimeter and submillimeter wave radiation sources and have attractive advantages for ESR spectroscopy, for example, high power and frequency tunability over broad range. The ESR device has been successfully applied to three cases of ESR measurements. In the first case, the temperature dependence of ESR was measured for a typical antiferromagnetic material MnO at the frequency of 301 GHz. In the second case, the dependence of the fine structure constant of the ruby on the magnetic field intensity was measured in the millimeter to submillimeter wave region. In these two cases, the gyrotron was operated by complete cw mode. In the final case, a pulse technique was applied to the ESR, the gyrotron was operated in pulse mode and the pulsed magnetic field was generated in the synchronized phase with the gyrotron operation. 相似文献
19.
Bin Li Xiaofang Zhu Li Liao Zhonghai Yang Baoqing Zeng Lieming Yao 《International Journal of Infrared and Millimeter Waves》2006,27(7):941-947
Two kinds of novel helical slow wave circuit, supported by Chemical Vapor Deposition (CVD) diamond, are presented. They are
applying in miniaturized millimeter wave helical traveling wave tube. Cold test characteristic of these circuits are simulated
by MAFIA code. Higher performances are achieved with smaller size, compared with conventional circuit supported by BeO rods.
The nonlinear analysis is implemented by Beam and Wave Interaction (BWI) module, which is a part of TWTCAD Integrated Framework.
Results have been found to be consistent with the expectation. It should be wider apply in microwave and millimeter wave vacuum
electronic devices. 相似文献
20.
Shunkang Liu 《International Journal of Infrared and Millimeter Waves》2003,24(7):1149-1158
The engineering design method of heliz-waveguide and rectangular coupled cavitiy-waveguide energy coupler employed in millimeter wave tubes is described. Experiments show that, the former has broadband matching character )VSWR is less than 2 at 26 - 40GHz). And the later has small reflection (VSWR is less than 1.5 at 34-37.5 GHz). Optimum design method of multi-section and linear taper waveguide impedance transformer is also given in this paper. These impedance transformers can operate at wide frequency range in microwave and millimeter wave band. The design method and examples of couplers and impedance transformers can be referred for tube designers. 相似文献