基于EMD方法的X波段双偏振雷达衰减订正

针对X波段双偏振雷达信号在降雨路径中的衰减现象,本文提出经验模式分解（Empirical Mode Decomposition,EMD）方法进行X波段双偏振雷达衰减订正,首先对总差分传播相移进行EMD分解得到有限个基本模式分量（Intrinsic Mode Function,IMF）,并基于皮尔逊相关系数准则将IMF分为噪声IMF和信号IMF两类,然后对信号IMF进行有效重构得到差分传播相移,再将差分传播相移通过最小二乘法拟合得到差分传播相移率,最后对求得的差分传播相移与差分传播相移率采用自适应约束方法进行反射率衰减订正。利用EMD方法和其他方法进行对比分析,其结果表明,EMD方法能够有效地消除X波段双偏振雷达回波数据中后向散射的影响,在保留真实的气象信息的同时,有效地抑制差分传播相移的显著波动,进而衰减订正效果更好。     

A Novel UWB (0.045–50 GHz) Digital/Analog Compatible MMIC Variable Attenuator With Low Insertion Phase Shift and Large Dynamic Range

A novel ultra-wideband (0.045-50-GHz) digital and analog compatible monolithic microwave integrated circuit (MMIC) variable attenuator with a low insertion phase shift and large dynamic range is presented. Based on our special design of both the series metal-semiconductor field-effect transistor (MESFET) and shunt MESFET control feeders, the MMIC possesses the feature of excellent return loss characteristic. Also, phase compensation techniques were used in the MMIC design to reduce the insertion phase shift when the attenuation varies. On-wafer measurement results of the developed MMIC chips in the 0.045-50-GHz band are minimum attenuation 2.0-4.0dB, and maximum attenuation >70dB, input and output VSWRles1.8 for all attenuation states; low maximum insertion phase shift of 0.86lesplusmndeg within 70-dB attenuation range. The chip size is 3.68mm times 1.58mm times 0.1mm     

The rain range experiment--Propagation through a simulated rain environment

The rain range experiment was conducted to test the adequacy of the assumptions usually made in the analysis of attenuation or phase shift due to rain: spherical drop shape, Mie scattering for a single drop, and single scattering theory for the coherent summation of the effects of each drop. A sprayer system was built that provided a stable drop size distribution that was measured and used for the estimation of the attenuation and phase shift on a line-of-sight measurement path through the spray. Measurements of attenuation and phase shift were made using vertical and horizontal polarization at 7.9 GHz and vertical polarization at 33.9 GHz. The results of the experiment show agreement between measurements and the theoretical model. The 7.9 GHz data also showed the attenuation and phase shift for horizontal polarization to be higher than for vertical polarization.     

A 360/spl deg/ Reflection-Type Diode Phase Modulator (Correspondence)

A 360/spl deg/ phase modulator using two series-tuned varactors in a parallel connection is described. The design minimizes the change in total phase shfit with frequency and gives a small attenuation ripple. The modulator is centered at 2 GHz and gives a total phase shift at 360/spl deg/ at the center frequency, an attenuation ripple of 1.3 dB over a 10-percent bandwidth and a 7/spl deg/ decrease of phase shift at the band edges.     

A wide range analog MMIC attenuator with integral 180° phaseshifter

A circuit topology is discussed for achieving a wide-range analog attenuator in MMIC form using enhancement mode FET's by combining it with a 90° phase shift network. By switching the phase shift network between a 90° phase lead high-pass structure and a 90° phase lag low-pass structure, a dual-purpose circuit is formed comprising both a variable attenuation and 180° phase shift function. The approach requires only a single control voltage for the attenuator and achieves an attenuation range of over 30 dB in L-band with less than 10° of phase imbalance over the range. In the low-loss state, the phase shifter achieves a 10° phase balance over a 250 MHz bandwidth with less than 0.3 dB of amplitude imbalance     

太赫兹波在均匀磁化等离子体中的传播特性

研究了太赫兹波通过均匀磁化等离子体的传播特性,给出了太赫兹波衰减和相移随等离子体密度、碰撞频率、太赫兹波频率和磁感应强度的变化规律。等离子体电子密度越大,衰减和相移越大;随着碰撞频率的增大,电磁波的衰减先增加到峰值后逐渐减小,且随着磁感应强度的增加,衰减的峰值变大,峰值向碰撞频率减小的方向移动;当电子碰撞频率接近电磁波频率时等离子体对右旋极化波的衰减达到极大值。太赫兹波频率增大,衰减逐渐减小,而相移先增加后逐渐减小。     

一种新颖的DC～50GHz低插入相移MMIC可变衰减器

介绍了一种新颖的 DC～ 5 0 GHz低相移、多功能的 Ga As MMIC可变衰减器的设计与制作 ,获得了优异的电性能。微波探针在片测试结果为 :在 DC～ 5 0 GHz频带内 ,最小衰减≤ 3 .8d B,最大衰减≥ 3 5± 5 d B,最小衰减时输入 /输出驻波≤ 1 .5 ,最大衰减时输入 /输出驻波≤ 2 .2 ,衰减相移比≤ 1 .2°/d B。芯片尺寸 2 .3 3 mm× 0 .68mm× 0 .1 mm。芯片成品率高达 80 %以上 ,工作环境温度达 1 2 5°C,可靠性高 ,稳定性好     

Propagation coefficients for vertically and horizontally polarised waves at 36.5 GHz

The differential attenuation and phase shift between vertically and horizontally polarised waves at 36.5 GHz have been measured on a 13.5 km link and compared with theoretical values from a field point matching analysis. It is seen that the differential phase shift is bounded in a small region about zero and changes in sign according to the size of drops involved, as predicted from theory. Differential attenuation also follows theoretical predictions with on-average values given by Laws-Parsons drop sizes.     

Ku波段6bit数字衰减器MMIC的小型化设计

基于0.25μm GaAs增强/耗尽(E/D)型赝配高电子迁移率晶体管(PHEMT)工艺,设计并实现了一款集成了6 bit并行驱动器的数字衰减器单片微波集成电路(MMIC)。该衰减器采用T型衰减网络结构,不仅缩小了芯片面积,并且可实现较好的衰减精度和衰减附加相移。芯片在片测试结果表明,在-5 V电源电压下驱动器的静态电流为1.8 mA,响应速度为25 ns。在9~18 GHz频率范围内,衰减器芯片的插入损耗不大于3.6 dB,均方根衰减精度不大于0.7 dB,衰减附加相移为-2°~4°,输入电压驻波比(VSWR)不大于1.25∶1,输出VSWR不大于1.5∶1。芯片尺寸为1.6 mm×0.6 mm×0.1 mm。该电路具有响应速度快、功耗低、面积小、衰减附加相移小等优点,可广泛应用于通信设备和微波测量系统中。     

广州地区1—400GHz降雨传播特性的计算

本文利用广州地区滴尺寸分布模型计算了１－４００ＧＨｚ线极化波雨 致特征衰减和相移，并利用计算的雨衰减和相移值回是了其与降雨率之间的指数关系。     

Backward and forward scattering by the melting layer composed ofspheroidal hydrometeors at 5-100 GHz

This paper addresses the behavior of the differential reflectivity, specific attenuation, and specific phase shift due to a melting layer composed of oblate-spheroidal hydrometeors. The results are based on a melting layer model and scattering computations derived from the point-matching technique with the truncation and recurrence adjusted. Computations at 5-100 GHz for five raindrop size distributions at rain rates below 12.5 mm/h are presented. In general, the reflectivity factor and differential reflectivity features with height at centimeter wavelengths agree with available radar measurements. At millimeter wavelengths, contributions to the radar backscatter from smaller hydrometeors become more and more important as the frequency increases and approaches 100 GHz. This should be instructive for utilizing millimeter wavelength radar techniques in radar remote sensing studies of the melting layer. Corresponding vertical profiles of the specific attenuation and phase shift are also presented at 5-100 GHz. The differential attenuation and phase shift indicate the particle shape effects. These attenuation and phase shift become more and more considerable as the frequency increases. Such forward scattering calculations should prove useful for studying propagation effects caused by the melting layer for satellite-earth communications, including depolarizations     

A simplified approach to the evaluation of EMW propagationcharacteristics in rain and melting snow

Electromagnetic propagation characteristics in rain and melting snow are calculated by treating these media as artificial dielectrics. Computed values of attenuation and phase shift in rain, obtained by this approach, are compared with those derived by using Mie scattering theory over a frequency range of 1-1000 GHz and for rain rates up to 100 mm/h. Very close agreement is generally obtained over these entire ranges. Melting snow is treated in the same manner, where comparison is possible these results tend to agree well with the available, but rather limited, published data. Attenuation and phase shift are calculated as a function of the degree of melting of the snow particles. Subject to assumptions relating the degree of melting to depth in the melting layer, average values of attenuation and phase shift are computed as functions of frequency. The attenuation values compare well with those derived from an empirical formula over the range of its validity     

广州地区33．5GHz和93GHz降雨传播特性测量

本文给出了１９９２年７—９月份广州地区Ｏ．４ｋｍ地面电路３３．５ＧＨｚ和９３ＧＨｚ雨衰减测量结果及雨衰减和降雨率短期统计结果之间的关系，并利用这一结果和长期降雨率统计对雨衰减预报作了初步探讨。同时分析了３３．５ＧＨＺ和９３ＧＨＺ雨衰减频率换算关系。文中还导出了雨致交叉极化鉴别度（ＸＰＤ）与实测差分衰减和差分相移之间的理论关系。在８ｍｍ波段可忽略差分相移的情况下，给出了利用３３．５ＧＨｚ部分实测差分衰减计算的ＸＰＤ结果，并与理论模式预测值作了比较。     

Characteristics of rain induced attenuation and phase shift at cm and mm waves using a tropical raindrop size distribution model

The tropical raindrop size distribution model developed by Ajayi and Olsen has been employed to study some characteristics of rain induced attenuation and phase shift for a tropical location for spherical, oblate spheroidal and Pruppacher-Pitter drop shapes. Parameters such as the a and b values for the power law relation between the specific attenuation and rainfall rate as well as differential attenuation and phase shift and their normalized values, were computed. A single power law between the specific phase shift and the rain rate was found to be adequate for vertical polarization, whilst a two-segment power law fitting is required for horizontal polarization between 1GHz and about 100GHz. The results were compared in many cases with those obtained with the Laws and Parsons drop size distribution, currently adopted by the CCIR for scattering applications.     

A dual-polarization rain profiling algorithm

A new attenuation correction algorithm based on profiles of reflectivity, differential reflectivity, and differential propagation phase shift is presented. A solution for specific attenuation retrieval in rain medium is proposed, which solves the integral equations for reflectivity and differential reflectivity with cumulative differential propagation phase shift constraint. The conventional rain profiling algorithms that connect reflectivity and specific attenuation can retrieve specific attenuation values along the radar path assuming a constant intercept parameter of the normalized drop size distribution. However, in convective storms, the drop size distribution parameters can have significant variation along the path. This paper presents a dual-polarization rain profiling algorithm for horizontal looking radars incorporating reflectivity as well as differential reflectivity profiles. The dual-polarization rain profiling algorithm has been evaluated with X-band radar observations simulated from drop size distribution derived from high-resolution S-band measurements collected by the Colorado Statue University CHILL radar. The analysis shows that the retrieved specific attenuation, differential attenuation, reflectivity, and differential reflectivity from the dual-polarization rain profiling algorithm provide significant improvement over the current algorithms.     

Effect of velocity mismatch and microwave attenuation ontime-domain response of traveling-wave electrooptic modulators

The dynamic response of a traveling-wave (TW) electrooptic phase modulator is treated using a Fourier transform technique. An integral expression for the induced phase shift which takes into account the optical-microwave velocity mismatch and the microwave attenuation is derived. In the case of a Gaussian modulating pulse and negligible microwave attenuation, the temporal dependence of the modulated pulse amplitude can be expressed in terms of error functions. Calculated pulse shapes showing the transition from a Gaussian to a flat top output pulse with increasing phase mismatch in the absence of microwave attenuation are presented. The effect of microwave attenuation on pulse shape, amplitude, and width is also explored. The method used to obtain these results is generally applicable to the time-domain analysis of TW modulators     

P-I-N Variable Attenuator with Low Phase Shift (Short Papers)

A broad-band MIC current-controlled variable attenuator that exhibits small phase change versus attenuation has been developed. Design factors that effect phase shift are discussed. Performance at frequencies between 0.5 and 3.0 GHz is shown. Measured values of attenuation are shown to be independent of frequency from 0.5 to 3.0 GHz.     

Comment on "A Simple Method for Measuring the Phase Shift and Attenuation Through Active Microwave Networks" (Correspondence)

In his recent letter on the measurement of phase shift and attenuation of active two ports Alday has submitted material which the author believes should not remain unchallenged. His notion of the addition of power in his system is an erroneous one, so that what he claims to be a measure of attenuation is in fact a measure of a quantity which is not an attenuation at all. It is, as will be seen, a quantity which qualitatively follows the "ups and downs" of a peculiar attenuation.     

The Effects Induced by Turbulence and Dust Storms on Millimeter Waves

Dust storms and turbulence consist of a random medium system, its effects on milimeter waves propagation are studied. Attenuation of millimeter waves, its phase shift and cross- polar discrimination are presented. Results show that dust storms mainly effects XPD and phase shift of millimeter waves, turbulence chiefly produces attenuation, in mediocre fluctuation.     

Separation of simultaneous rain and ice depolarization

In the case of depolarization due to rain or to ice crystals, the differential attenuation, the differential phase shift, and the canting angle of the depolarizing medium can all be calculated independently from dual polarized measurement results. However, this is not possible when rain and ice are causing depolarization at the same time. This paper presents a calculation method which makes it possible to derive during simultaneous rain and ice depolarization some of the characterising parameters of each part separately. The method makes use of an a priori known relation between the differential attenuation and the differential phase shift of rain and of ice. The calculation method is tested on measured depolarization events, and yields good results.