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.     

Rain induced cross polarization at millimeter waves in a Xi'an environment

The rainfall intensity accumulative distribution, raindrop size and canting angle distributions in Xi'an(108.9 E, 34.3 N) have been obtained from data measured over a long period of time. Rain induced crose polarization in this environment has been studied. The crose polarization discrimination, XPD, was compu ted over a frequency range of 19.3 to 300 GHz for non spherical drops. The variations of XPD with frequency, rainfall rate and copolar attenuation, CPA, were investigated. The computational resulte are in good agreement with experimental data. A mathematical relationship was established between the XPD and CPA, raindrop canting angle, which result is in good agreement with experimental data. The cumulative distribution of rain induced cross polarization for eleven years and in month have been ob tained with the cumulative distribution of the rain rate from the data measured from 1975 to 1985. The role of multiple scattering also has been discussed, it is shown that the multiple scattering play an important part in short millimeter wave.     

Worst month statistics of attenuation and XPD on Earth-space path

Using the attenuation and cross-polarization discrimination (XPD) statistics measured in the CS (20/30 GHz) and BSE (12/14 GHz) centimeter wave propagation experiments performed for over four and three years, the worst month statistics of attenuation and those of XPD on earth-space path at 11.7 and 19.5 GHz are derived. The probability relation between the annual and worst month statistics is approximated by a power-law relation, and the constants for the relation are derived by a least squares procedure. It is found that the relation is independent of both frequency and polarization. The cumulative probability ratios of the worst month to annual statistics at the same attenuation or XPD values are derived as a function of annual cumulative probability. The ratios are well described by the Brussaard model of the worst month statistics. Attenuation ratio and XPD difference among the annual and worst month statistics are also derived and compared with the predicted results.     

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。     

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.     

Depolarization measurements at 11.6 GHz on Earth-space paths using the SIRIO satellite

Depolarization (XPD) data at 11.6 GHz in circular polarization collected during the SIRIO experiment on the Italian stations of Fucino and Lario are presented and analyzed. The obtained results are presented both in conditional form (i.e., XPD statistics conditioned to the co-polar attenuation (CPA)) and in "equiprobable" form (i.e., by comparing XPD-CPA values exceeded for the same fraction of the total observation time). The conditional XPD appears spread in an interval ofpm5dB around the conditional median value. This latter appears to be very close to the "equiprobable" value. The International Radio Consultative Committee (CCIR) procedure giving the "equiprobable" XPD appears fairly well supported by the Fucino data, while the Lario data give higher depolarization than predicted by CCIR.     

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     

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.     

用于交通监测的机动车轮毂散射特性

提出了一种利用机动车轮毂正交极化散射实现交通流量监测方案,研究分析了机动车轮毂极化电磁散射特性,得出了优化参数。通过建立汽车和轮毂模型,仿真得到主模谐振频率为255 MHz,比较了入射波激励为线极化平面波时,汽车和轮毂主极化、正交极化雷达散射截面(RCS)的大小,并得到了单个轮毂正交极化雷达散射截面达到最大值时的入射角。仿真比较了入射波极化角度改变时,RCS 的空间分布特点。分析表明:轮毂目标VH 极化散射最显著;将雷达天线放置于与机动车轮毂中心相对地面同等高度处,可有效减小机动车框架对轮毂散射场的影响,研究结果对于构建经济有效的机动车交通管制系统具有实际意义。     

Multigigabit transmission through rain in a dual polarizationfrequency reuse system: an experimental study

An experimental terrestrial link was set up for the purpose of evaluating very-high-data-rate communications in dual-polarization frequency reuse systems. Possible applications are in the field of satellite communications. Two 3.2-Gb/s signals using staggered quadriphase shift keying (SQPSK) were transmitted on opposite senses of circular polarization over a 7-km path located in Crane rain region D3. Performance degradation of the demodulator as a function of cross-polarization discrimination (XPD) was evaluated and found to closely match simulation predictions. However, the relationship between XPD and rain attenuation was found to be more complex than thought previously, displaying a relatively slowly varying hysteresis effect as well as significant interactions with characteristics of the receive antenna. The latter effect suggests that careful control of antenna characteristics may be required if such high-data-rate techniques are to be employed in space-ground links     

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.     

双波长波片导致的脉冲分离对双色场辐射太赫兹波的影响

由于群速度的偏振依赖性,飞秒激光脉冲入射到双波长波片时出射光脉冲会分离为两个具有一定时间延迟的飞秒激光脉冲。从实验和理论模拟两方面研究了双波长波片导致的脉冲分离现象对飞秒激光双色场成丝辐射太赫兹(THz)波效率的影响。实验结果表明,脉冲分离导致的时间延迟会降低双色场辐射THz波的效率,可通过零级双波长波片缩短分离脉冲之间的时间延迟,有效提高THz波的产生效率。     

Data analysis for dual-polarized communication link experiments

Performance of dual-polarized radio links operating in the microwave and millimeter wave regions is affected by the propagation medium. The attenuation (A) and cross-polarization discrimination (XPD) are used to quantify the medium effects. Of particular importance is the XPD versusArelationship. Three ways of displaying XPD versusAdata are examined: mean, median, and equiprobable. It is shown that mean and medium are essentially identical measures, whereas equiprobable is sensitive to several error sources and is especially sensitive to ice depolarization. It is concluded that XPD versusAdata sets using mean and median can be safely compared, but equiprobable results must be treated with caution.     

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     

反射式液晶器件振幅调制特性的研究

研究了反射式液晶器件(RLCOS)的振幅调制特性.采用2×2的琼斯矩阵计算仿真,从理论上分析了它的振幅调制特性.实验采用He Ne激光为光源,将反射式液晶器件显示器作为液晶空间光调制器,用计算机和相关的电路系统驱动控制,并用CCD采样数据,测试了1024×768反射式液晶器件显示器的振幅调制特性.与未改形光束剖面相比,在特定的入射、出射偏振光配制下,可以用反射式液晶器件显示器来做振幅调制器.     

人体附近天线的辐射特性

使用解析方法研究了无线人体局域网(WBAN)通信中穿戴式天线的辐射特性.将人体简化为有耗介质椭圆柱体,采用椭圆柱面波展开和阻抗边界条件(IBC),利用收、发天线的互易原理,推导了置于人体附近的短振子天线之方向性图和增益的解析表达式.计算了不同极化取向以及离人体不同间距对天线辐射特性的影响.经与软件仿真和实验测试结果对比...     

Polarization transformation of a wave field propagating in ananisotropic medium

The momentous experimental discovery of the Faraday (1846) effect is sketched from a historical perspective, through the eyes of several well-known scientists. This effect and its generalization can be explained theoretically by using the dispersion theory for waves propagating in an anisotropic medium. A wave of arbitrary initial polarization will have its wave polarization transformed continuously as it propagates. It is convenient to represent this continuous polarization transformation by a locus in the polarization-ratio plane. In a lossless medium, when both characteristic waves are propagating, this locus is a circle. Five cases in a magneto-ionic medium have been investigated for different propagation angles. The results are discussed and illustrated     

A multifrequency adaptive radar for detection and identification of objects: Results on preliminary experiments on aircraft against a sea-clutter background

An experimental model of a simple multifrequency continuous wave (CW) radar system has been developed. Preliminary experiments have been performed in order to illustrate the potential of this radar concept in regard to detection, course ranging, and also identification of low flying aircraft against a sea-clutter background. The radar can be organized so as to measure ocean wave height, wave direction, and wave velocity simultaneously for 15 different ocean wavelengths ranging from 150 m to approximately 6 m. An example of such a directional wave intensity spectrum is given. To illustrate the ranging and the identification potential of the technique in regard to airplanes, two different airplane categories, namely a propeller aircraft (Cessna 172) and a rigid jet aircraft (F-16), were flown through the radar beam. The signatures of these two airplanes are show in two signature domains: spatial distribution of scattering centers and motion pattern. The experimental results confirm theories presented in earlier contributions. It remains to introduce two more domains, namely the space/time coherence properties of the target and its polarization characteristics.     

GPS海面散射信号探测技术研究

该文简述了利用GPS散射信号进行微波遥感的背景和优点,并从GPS海面散射信号极化特性、信号波动情况、波程差引起散射信号相对直射信号的码延迟以及由于海面粗糙度引起的散射信号相关功率扩散几个方面详细分析了海面散射GPS信号检测技术。给出了自行研制的延迟映射接收机的工作原理, 在天津近海进行了首次搭载飞行试验,数据分析结果与理论分析符合。