SDH微波传播中多径衰落对XPD的影响

论述了数字微波通信中天线方向性对交叉极化鉴别度（ＸＰＤ）的影响,以及等效瑞利衰落概率和ＸＰＤ恶化量的关系,最后说明只要采取一定的技术措施就可以减少多径衰落对ＸＰＤ产生的恶化影响     

The Feasibility of Two One-Parameter Polarization Control Methods in Satellite Communications

The orthogonal polarization techniques will be widely used in satellite communications due to its efficient utilization of the spectrum, but the feasibility of different methods to compensate for the cross-polarization at ground stations will be essential for the applicability of the techniques. Although complicated four-variable systems have been designed by many groups, two simple one-parameter methods have been proposed recently. The first, rotational compensation, simply rotates the linear polarization directions of the receiving antenna to maximize XPD; the second, quadrature cancellation, simply injects quadrature cancelling signals. This paper studies the feasibility of these two methods in terms of system designer's viewpoints. A correlation approach is used to estimate the achievable XPD values for different situations including rain, ice particles, and Faraday rotation. The system availability and cost considerations are analyzed using a possible tradeoff between CNR and XPD values. The control errors and stability problems are also discussed. The results indicate that there exist many situations in which these one-parameter methods are feasible and attractive and provide possible solutions for designers desiring effective, low-cost receiving stations with satisfactory performance.     

Centimeter wave propagation experiments using the beacon signals of CS and BSE satellites

The wave propagation experiments using Japanese geostationary satellites CS (20/30 GHz) and BSE (12/14 GHz) satellites have been performed at the Kashima earth station of the Radio Research Laboratories (RRL). Cumulative rain attenuation and cross-polarization discrimination (XPD) statistics are given for the period of three years at 11.7 GHz (vertical polarization) and for the period of four years at 19.5 GHz (circular polarization). It is shown that the yearly rainfall rate and attenuation distributions are well approximated by log-normal distributions, and the XPD distribution is well approximated by a normal distribution. Monthly and time-of-day variation of the attenuation and XPD distributions are presented. Duration statistics of attenuation and XPD are presented and characterized. Other characteristics in the wave propagation, such as effective path length, frequency dependence of attenuation, and joint statistics of attenuation and XPD are derived and discussed. Rainfall events are classified into three rainfall types, "stratus," "cumulus," and "others" using measurements of the radar reflectivity factor along the satellite-to-earth path, and the dependence of XPD characteristics on the rainfall type is also presented and discussed. Some prediction methods of calculating attenuation and XPD statistics are applied to the data obtained in these experiments and the predicted results are compared with the measured ones. It is found that some corrections are needed when the XPD statistics are predicted from the attenuation statistics using the theoretical relation between XPD and attenuation.     

Analysis of the effects of water on the ACTS propagation terminal antenna

The NASA advanced communications technology satellite (ACTS) propagation experiment was designed to observe the attenuation produced by rain on Earth-satellite paths operating in the Ka-band. Unwanted effects of water on the antenna reflector surface were noted. Wet-antenna attenuation could be attributed to the combined effect of a water layer on the reflector surface and water wetting the feed window surface. A model was developed to calculate the antenna reflector and feed surface water layer thickness values as a function of position on each surface. The thickness values were used to calculate the additional attenuation produced by the water layers as a function of rain rate on the antenna. The wet-antenna-attenuation prediction model was verified by sprayer tests. The goal of the ACTS propagation experiment was to obtain path attenuation statistics, statistics that represent the effects of rain on the Earth-satellite path but not on the antenna itself. The wet-antenna attenuation prediction model was used to remove the effects of water on the antenna from the combined antenna-plus-path attenuation statistics produced by the experiment. The overall efficacy of the model was demonstrated by comparing the corrected path loss statistics from two ACTS propagation experiment sites with earlier COMSTAR path loss measurements made at or near those sites. The empirical distribution functions from both the ACTS and COMSTAR experiments were identical within the expected uncertainty of an empirical annual distribution of attenuation by rain.     

天线罩去极化效应及其补偿

天线罩在对天线起到保护作用的同时,也导致了线极化电磁波通过它时必将产生的去极化效应,从而大大影响了通信质量,这主要是因为天线罩对垂直极化分量和平行极化分量的传输系数不同所致。为提高通信系统的交叉极化隔离度,更好地进行通信,对天线罩去极化效应进行了计算,根据计算结果进行了仿真,并设计了补偿电路。结果表明,通过该方法补偿后,能有效提高通信系统的交叉极化隔离度,减少天线罩去极化效应对通信的影响。     

Polarization measurements and modeling in indoor NLOS environments

Cross-polarized antenna systems are an attractive way to reduce equipment size while maintaining low interantenna correlation. In this paper, the polarization behaviour of indoor channels is investigated. A measurement campaign has been conducted at 3.6 GHz for a dual-polarized transmitter and a tri-polarized receiver in a non-Line-of-Sight (NLOS) scenario. The spatial and delay characteristics are extracted using a pertap beamforming algorithm. Distinct paths are isolated and the polarization of each wave is expressed in terms of its spherical components. The cross-polarization discrimination (XPD) of the wave is investigated as a function of its physical propagation parameters. The XPD of the wave is shown to be sensitive to spatial characteristics, while being insensitive to delay.     

Prediction of rain effects on earth-space communication links operating in the 10 to 35 GHZ frequency range

This paper reviews the effects of precipitation on earth-space communication links operating the 10 to 35 GHz frequency range. Emphasis is on the quantitative prediction of rain attenuation and depolarization. Discussions centre on the models developed at Virginia Tech. Comments on other models are included as well as literature references to key works. Also included is the system level modelling for dual polarized communication systems with techniques for calculating antenna and propagation medium effects. Simple models for the calculation of average annual attenuation and cross-polarization discrimination (XPD) are presented. Calculation of worst month statistics are also presented.     

X型极化分集系统中天线互耦效应分析

极化分集系统的分集增益性能受天线阵元间互耦因素的影响很大。为了探究存在互耦效应时天线分集增益与阵列夹角之间的关系,首先基于天线基本理论,推导出X型极化分集阵列互耦阻抗、空域相关性以及平均功率比等参数的显性数学表达式,并据此详细研究存在阵列耦合时,X型极化分集系统分集增益性能随阵列排布夹角而改变的变化趋势。理论分析与计算机数值仿真结果皆表明：引入阵列互耦效应后,X型极化分集阵列的分集增益性能优于不计互耦效应时的阵元夹角范围,将随着交叉极化鉴别度的增大而增大。鉴于实际通信环境大多处于较高交叉极化鉴别度值的情形,故此研究结果可为多输入多输出（MIMO）系统小型化设计提供重要的理论及数值分析参考。     

Radio propagation for space communications systems

This paper presents a review of the most recent information on the effects of the earth's atmosphere on space communications systems. The design and reliable operation of satellite systems which provide the many applications in space and rely on the transmission of radio waves for communications and scientific purposes are dependent on the propagation characteristics of the transmission path. The presence of atmospheric gases, clouds, fog, precipitation, and turbulence cause uncontrolled variations in the signal characteristics which can result in a reduction of the quality and reliability of the transmitted information. Models and techniques used in the prediction of atmospheric effects as influenced by frequency, geography, elevation angle, and type of transmission are discussed. Recent data on performance characteristics obtained from direct measurements on satellite links operating to above 30 GHz are reviewed. Particular emphasis is placed on the effects of precipitation on the earth-space path, including rain attenuation, and rain and ice-particle depolarization. Sky noise, antenna gain degradation, scintillations, and bandwidth coherence are also discussed. The impact of the various propagation factors on communications system design criteria is presented. These criteria include link reliability, power margins, noise contributions, modulation and polarization factors, channel crosstalk, error-rate, and bandwidth limitations.     

Effect of rain in the near field of an antenna

The effect of rain on the field at a point irradiated by a microwave antenna is found, in contrast with previous work, to be effectively independent of the parameters of the antenna. The standard Fresnel zone criterion for the `active rain volume? has been extended to treat rain in the near field of the antenna.     

Small-scale variations of cross-polar discrimination in ricean fading channels

Cross-polarised antenna systems are an attractive way to reduce equipment size while maintaining low inter-antenna correlation. The cross-polar discrimination (XPD) is an important parameter of crosspolarised systems. Starting from the definition of Ricean fading channels, it is shown that the small-scale variations of the XPD have a doubly non-central F-distribution. The simulated XPD distribution obtained as a function of the Ricean parameters is successfully compared with measurement results for validation.     

Rain induced depolarization from 1 GHz to 300 GHz in a tropical environment

The rain induced depolarization in a tropical environment has been studied using a tropical raindrop size distribution developed by Ajayi and Olsen (A-O). The differential attenuation, differential phase shift and cross polarization discrimination, XPD, were computed over a frequency range of 1GHz to 300GHz for spheroidal drops and up to 33GHz for Pruppacher-Pitter drops. The variations of XPD with frequency, rainfall rate and copolar attenuation, CPA, were investigated. A mathematical relationship was established between the XPD and the CPA, canting angle and frequency of propagation from 5GHz to 300 GHz for spheroidal drops and up to 33 GHz for Pruppacher-Pitter drops. The results obtained using the A-O drop size distribution have been compared with those assuming the Laws and Parsons (L-P) distribution. The Pruppacher-Pitter drop shape has been found to give rise to higher XPD, especially at low CPA and high frequencies.     

Cross polarization on line-of-sight links in a tropical location:effects of the variation in canting angle and rain dropsizedistributions

The effects of the variation in canting angle of falling raindrops and the distribution of raindrop sizes in different types of rain on cross polarization discrimination (XPD) on line-of-sight propagation paths in a tropical location in the frequency range 1-50 GHz are investigated. The dropsize distribution (DSD) model of Adimula and Ajayi (see Ann. Telecomm., vol.51, no.1/2, p.87-93, 1996) has been used. Although, some previous studies of XPD assumed equi-orientation of the raindrops along the propagation paths, the present study employs the more realistic distribution of canting angles along the path. The results obtained show that the XPD improves by about 4-7 dB over those based on the equi-orientation model. It is also shown that for the same copolar fade and for frequencies greater than about 10 GHz, the variation of the XPD with copolar attenuation (CPA) is relatively insensitive to the assumed DSD in rain and that the deterioration in signal quality or outage will be influenced more by the signal attenuation rather than by the cross-polarization interference     

Microwave depolarization versus rain attenuation on earth space in Malaysia

The wave propagation experiments using Japanese geostationary satellite Superbird‐C have been performed at the Universiti Sains Malaysia earth station. A relationship between rain depolarization and attenuation, valid for earth‐space path at microwave wavelengths, is presented. Cumulative rain attenuation and cross‐polarization discrimination (XPD) statistics are given for the period of 4 years (2002–2005) at 12.255 GHz. XPD varied from 44 dB at 1% to 16 dB at 0.001% of time the abscissa is exceeded. Comparisons were made with available data sets and with five simple XPD models and the results indicate a good performance by the simple isolation model and the CHU model compared with the others. These results serve as checks on the theoretical models needed for predicting communication system performance in geographical regions especially for equatorial climate where measurements are not available. Copyright © 2008 John Wiley & Sons, Ltd.     

Specification of polarization parameters for optimal-performance inrain of dual circularly polarized radio links

Rain depolarization of nominally circularly polarized waves alters the polarization state of the wave to produce a polarization ellipse in which the major axis is tilted with respect to the horizontal. Tilt angles for right-hand and left-hand polarization are opposite in sign. It is shown that these tilt angles are almost independent of rain rate and only slightly dependent on frequency. At 62 GHz the magnitude of tilt is close to 60°C. The suggestion is made that the antenna system be deliberately designed to match, as closely as possible, the polarization state of the incoming wave when the expected rain attenuation is at the design maximum (rain margin) for a given communications link. This strategy assures that the crosstalk between polarizations will be minimized when the signal-to-thermal noise ratio (SNR) is at its lowest value. In clear weather, the SNR will be larger, and a greater degree of polarization crosstalk can be tolerated. Finding an optimal match involves selection of the correct rotational orientation of at least one of the antennas as well as specification of its axial ratio to lie between minimum and maximum limits     

Estimation of cross-polarization due to rain over some stations in Nigeria

The statistical morphology of cross-polarization due to rain is of considerable interest to system designers in order to estimate accurately the signal total availability of time. In this paper, an attempt has been made to compute cross-polarization of millimeters waves in the Ku- and Ka-band frequencies range due to rain. ITU-R P.618-9 model has been used to predict cross-polarization discrimination (XPD) over three different elevation angles in Nigeria with modification using log-normal distributions of raindrop sizes at 20°C and assuming circular polarization for Earth–satellite propagation paths. The study includes a number of earth stations in Nigeria, namely Akure, Ikeja, Calabar, Minna, and Kano. Variations of co-polar attenuation with XPD as well as cumulative distribution of XPD have also been presented. The result of the estimation of XPD at various elevations angles and at the frequencies considered shows the dependence of XPD on frequency, co-polar attenuation, and rainfall rates. The orthogonal channels at the same frequency situated at the coastal region is prone to higher amount of unwanted signal mostly at the elevation angle of 23° (for communication links over the Indian Ocean) than at other elevation angles considered in this report.     

5G毫米波短距离链路雨衰减特性分析

雨衰减严重影响第5代(the 5th Generation,5G)移动通信系统性能.在路径长度小于1 km的短距离链路情况下,现有雨衰减预测模型调整因子大于1,导致预测雨衰减随路径变短而增大,无法支撑毫米波短距离链路系统设计.通过分析国际电信联盟无线电通信部(Radiocommunication Sector of International Telecommunication Union,ITU-R)短距离链路雨衰减试验数据,发现湿天线衰减与路径雨衰减相当,得到毫米波短距离链路必须考虑湿天线衰减的结论.建立了湿天线衰减与降雨率的关系模型,分频段对模型参数进行了拟合,拟合结果与实测数据吻合得较好.提出了考虑湿天线衰减的短距离雨衰减建模新思路,可解决短距离雨衰减预测问题.研究结果有助于提高5G毫米波系统余量设计的可靠性.     

Computer simulation of the human-body effects on acircular-loop-wire antenna for radio-pager communications at 152, 280,and 400 MHz

This paper presents an extensive computer simulation of the influence of the human body on a circular-loop-wire antenna to simulate the pager antenna. The coupled integral equations (CIEs) approach and the method of moments (MoM) are employed for numerical simulation of this antenna-body-coupling problem. The magnetic frill source is used to model the antenna-feeding structure. A realistically shaped full-scale human-body model (1.7 m) is constructed. A small loop antenna (loop radius b=1.7 cm and wire radius a=0.072 cm) of x, y, and z orientation, in free space or proximate to the human body at the top pocket (chest position) or belt level (waist position), is considered. Numerical results of the antenna characteristics and body absorption at 152, 280, and 400 MHz are presented and discussed for radio-paging applications. At 280 MHz, it is found that the real part of the impedance increases about five to ten times, and, hence, the antenna ohmic-loss radiation efficiency increases from 17% (in free space) to 69%, 44.3%, and 58.4%, respectively, for the x-, y-, and z-oriented loops when proximate to the body. The radiation efficiencies, reduced by the body-absorption effect, are 5%, 61%, and 25% for the x-, y-, and z-oriented loops, respectively. For the y-oriented loop, which is found to be the most suitable for paging communications, the antenna efficiencies are almost the same at the two location levels for all frequencies considered. The computed antenna characteristics influenced by the human body; including the input impedance, antenna patterns, cross-polarization field level, radiation efficiencies, and maximum and minimum power gains, are important for the antenna/RF design and the link-budget consideration     

Axial crosspolarization in reflector antennas due to asymmetric cross-polar feed patterns

The on-axis cross-polarisation of a reflector antenna illuminated by a feeding system with an asymmetric cross-polar radiation pattern is examined. A graph is presented from which the cross-polarisation discrimination (XPD) of the reflector antenna can be simply obtained.     

Performance of shorted microstrip patch antennas for mobilecommunications handsets at 1800 MHz

We have investigated the application of two different types of novel shorted-patch antennas for mobile communications handsets at 1800 MHz. A single shorted-patch and a stacked shorted-patch antenna offering improved bandwidth are compared with data for a λ/4 monopole. The finite-difference time-domain (FDTD) technique was used to calculate antenna characteristics such as impedance and radiation patterns for two cases: on a handset and on a handset near a (2.5-mm voxel) heterogeneous head model in an actual position of phone use. We also obtained specific absorption rate (SAR) distributions and calculated the spatial peak 1-g SAR values. In addition, the effect on SAR and antenna characteristics of including a block model of the hand was assessed. Similar performance is achieved from the single or stacked shorted-patch antenna with the latter providing greater bandwidth, 8.2% versus 9.4% with the head and hand included. Both antennas reduce the l-g spatial peak SAR value in the head by 70% relative to the monopole. The presence of the hand reduces the efficiency of all three antenna types by approximately 10%