Cloud Characteristics and Cloud Attenuation in Millimeter Wave and Microwave Frequency Bands for Satellite and Remote Sensing Applications over a Northern Indian Tropical Station

Microwave and millimeter wave frequency bands are in demand for requirement of more channels in radio communication systems. It has also been recognized that microwave and millimeterwave frequency radiometers on board satellites as promising tools for remote sensing.The frequency more than 10 GHz is affected by rain and cloud. Though the effects of rain on radiowave is more than cloud but the occurence of cloud is more than rain. Cloud has been found to occur for weeks together over this part of the world. It is therefore essential to study cloud morphology over different geographical region.In this paper, an attempt has been made to the cloud occurrences over an Indian tropical station, Delhi (28.35°N, 77.12°E) observed during different months and daytime and nighttime. It is seen that low clouds occurrence over Delhi is very significant and particularly during July, August and September. The specific attenuation of radiowave due to clouds at various frequencies 10 GHz, 20 GHz, 50 GHz and 100 GHz has been deduced. The specific attenuation of radio wave due to cloud at 10 GHz varies from 0.0608 dB/km to 0.1190 dB/km while at 100 GHz the specific attenuation varies from 6.8460 dB/km to 11.9810 dB/km     

Cloud Attenuation in Millimeter Wave and Microwave Frequencies for Satellite Applications over Equatorial Climate

A propagation experiment has been carried out at Penang using the SUPERBIRD-C satellite beacon. Cloud occurrences were observed during different months and it is seen that the low cloud occurrences over Penang is very significant from October to January. The cloud attenuation results that are presented, which include the testing of models, have been obtained from the data gathered over five years. The specific attenuation of radio wave due to clouds at various frequencies 12 GHz, 20 GHz, 75 GHz, 50 GHz and 100 GHz has been estimated whereby the values varies from 0.14 dB/km at 12 GHz to 10.1 dB/km at 100 GHz.     

Cloud Morphology Over Three Indian Tropical Stations for Earth Space Communication

Microwave and millimeter wave frequency bands are in demand for requirement of larger bandwidth for various applications of radio systems. In future in India too, microwave and millimeter wave frequencies will be in use very extensively for radio communication purposes and remote sensing applications. But, the attenuation due to cloud as well as thermal noise associated with could in millimeter wave and microwave frequency bands are of great concern to system engineers and radio researchers. Both cloud attenuation and cloud noise temperature lead to degradation in the performance of microwave communication and radar propagation. The effects of rain on radio wave are more than cloud but the occurrence of cloud is more than rain. In some parts of India cloud occurs for weeks together. The cloud morphology particularly in relation to radio wave propagation over different geographical region of India is therefore very essential and important. In view of this, systematic studies on cloud occurrence morphology over different geographical locations in India have been undertaken. In recent past some results on cloud occurrences over different stations in India have been reported. In this paper, cloud characteristics and cloud attenuation over three more stations are presented. Based on low level cloud coverage observations, cloud occurrences frequency over Mumbai (19.07°N, 72.50°E), Nagpur (21.06°N, 79.03°E) and Ahmadabad (23.04°N, 72.38°E) situated in Indian tropical west coast, central plain and semi arid region of western India in different months during daytime and nighttime has been deduced. The low-level cloud over Mumbai, Nagpur and Ahamedabad has been found to occur for many days and nights and particularly in the months of June, July, August and September. The attenuation of radio wave due to clouds at various frequencies ∼10, 18, 32, 44 and 70 GHz over the aforesaid three stations also been deduced.     

磁化碰撞等离子体对雷达波的共振吸收

使用平板几何对雷达工作频段的电磁波在磁化碰撞等离子体中的传播作了数值计算,计算结果表明,在均匀等离子体中,当等离子体碰撞频率f∞=0.1,0.5,1GHz及电磁波频率接近高混杂频率时,电磁波衰减和被吸收功率出现最大峰值,即出现共振吸收;当fen=1,10GHz时,电磁波衰减、被吸收功率和透射功率曲线变得很平坦;衰减和吸收功率随等离子体密度的增大而增大,在n=10^11cm^-3时,衰减可达100dB,吸收比可达80％。在非均匀等离子体中,电磁波的反射功率峰值比在均匀等离子体中大。因此,磁化均匀等郭了体更有利于等离子体隐身。     

Millimeter-Wave Attenuation Due to Fog and Clouds

The parameters of gamma drop size distribution model of fog and clouds are derived based on the liquid water content and optical visibility, the attenuation are calculated and discussed with this model and empirical relations of the liquid water content and the visibility or other parameters of fog and clouds. A new empirical formula to estimate fog and clouds attenuation is presented based on the Reyleigh absorption approximation, which is more accurate in general and can be used in wider frequency and temperature range than other empirical formulas.     

The main results of cloud and rain remote sensing by multichannel microwave radiometry

The basic results have been considered for multiwave remote sounding of the troposphere with clouds and rain from ground-based station in the zenith direction. The radio wave scattering by rain drops as well as variation of vapour content in the atmosphere during measurements are taken into account when processing of the experimental data. A separation of the complete attenuation in clouds with rain has been made over three components: due to vapour, cloud and rain. A relation is considered of millimeter and centimeter wave attenuation in clouds with rain between each other and with the rain intensity. A behaviour of the relation of attenuation structural functions is explained. The Diagnostic problems of millimeter wave attenuation are considered.     

Radio frequency characteristics of Fe-filled carbon nanotube film

The conduction noise suppression in radio frequency region using film type of the Fe-filled carbon nanotubes and its epoxy composite was evaluated on a coplanar waveguide. Fe in carbon nanotubes have shown α-Fe crystalline structure and had a coercivity of 650 Oe. The magnitudes of the signal attenuation of Fe-filled carbon nanotubes on coplanar waveguide were shown in the range of about 10–18 dB/cm at 20 GHz (the stop-band frequency region). The power losses of these films exhibited 65–85% at 20 GHz in the stop-band frequency.     

基于数字相干叠加的相干光正交频分复用系统中光纤非线性容忍性研究

光正交频分复用系统中的光纤非线性效应制约着系统进一步的扩容. 针对此问题, 提出一种数字相干叠加的方法, 用于提高相干光正交频分复用系统对光纤非线性的容忍性. 仿真中, 5通道的波分复用下偏振复用相干光正交频分复用系统的每个通道传输四进制正交振幅调制映射的71.53 Gbit/s信号在光纤中传输400 km. 首先, 通道间隔为25 GHz, 与传统相干光正交频分复用系统相比, 色散补偿前后, 使用数字相干叠加的相干光正交频分复用系统的信噪比分别提升了6.02 dB和9.05 dB, 最佳入纤光功率均增大了2 dB; 其次, 通道间隔为50 GHz, 色散补偿前后, 信噪比分别提升了4.9 dB和8.75 dB. 通过理论推导及仿真, 验证了所提方法能有效消除相干光正交频分复用系统的一阶非线性失真, 进而提高系统对光纤非线性的容忍性.     

Temperature Effects on Attenuation Due to Rain for Millimeter and Centimeter Waves

Radio wave operating in millimetrewave and microwave frequency bands are adversely affected due to rain. Particularly the attenuation is of immense significance for sensitive remote measurements by satellites using frequencies greater than 10 GHz. Maintenance of an uninterrupted communication link requires a precise knowledge of the attenuation effect due to rain for commissioning right kind of transmitting sources for various purposes required in present day situation. Precise measurement of attenuation at various frequencies will enable us to choose the right frequency, polarization, incident angle and power of the source for different purposes. In this paper we have compared the results of earlier works using aR^b Olsen et al, (1) and the formulation by Moupfouma, (2) on the basis of theoretical analysis for explaining the observed results. Effect of temperature, considered in detail in this communication, has contributed the necessary correction factor of the rain attenuation for explaining the observed results. Theoretical analyses to measure the attenuation of the propagating wave due to temperature variation in the rain path have been presented. Correction factor due to temperature profile (temperature from the ground to the rain height within which the radio wave traces its path) has been incorporated in two models by using the concept of dipole energy changes. The effect of this temperature is noted to be quite significant and incorporates an error to the extent of 7–8%.     

电推力器等离子体喷流对航天器通讯电磁波信号衰减效应

采用时域有限差分法计算了不同特性电推力器等离子体喷流对不同频率通讯电磁波的衰减系数,采用空间透射波法进行了微波等离子体推力器喷流对C波段电磁波衰减的地面测试实验。理论计算和实验诊断结果表明:电推力器等离子体喷流对电磁波的衰减系数随着电磁波频率的升高逐渐减小,随着喷流等离子体频率的升高近似线性增大,随着喷流等离子体碰撞频率的增大呈先增大后减小的趋势;当喷流中等离子体数密度为0.9×1016~1.8×1016m-3时,C波段电磁波的衰减系数为1.5~6.0 dB,电推力器等离子体喷流对通讯信号的衰减效应不可忽略。     

实心砖墙对电磁波的衰减特性

应用模式传输线理论分析了多层周期介质实心砖墙对电磁波的衰减特性。计算得到了电磁波穿透实心砖墙的透射反射系数与入射角和频率的关系曲线,数值计算的结果与软件仿真的结果符合较好。利用电磁波测量系统测量得到了实心砖墙对电磁波衰减随频率（2~8 GHz）的变化关系。综合考虑数值计算和实验测量的结果,得到频率为2~8 GHz时,实心砖墙对电磁波的衰减为15~25 dB。     

三角形栅格矩形径向线螺旋阵列天线的设计与实验研究

 介绍了三角形栅格矩形径向线螺旋阵列天线的工作原理,设计并数值模拟了中心频率为4.0 GHz的三角形栅格矩形径向线螺旋阵列天线,并对此阵列天线进行了实验研究。实验结果表明：阵列天线在中心频率4.0 GHz 下,增益为15.3 dB,轴向轴比值1.58,驻波比为1.3,口径效率为86%;在3.8～4.2 GHz的频率范围内可实现圆极化定向辐射,增益大于14.9 dB,轴比值小于1.7,驻波比小于1.6。     

同轴转弯波导的设计与实验研究

提出了一种同轴转弯波导。介绍了该同轴转弯波导的基本原理,设计并数值模拟了中心频率为4.0 GHz的同轴转弯波导,并对此同轴转弯波导进行了实验研究。实验结果表明:同轴转弯波导在中心频率4.0 GHz下,传输损耗约为0.17 dB,驻波系数为1.2;在3.8~4.2 GHz的频率范围内传输损耗小于0.2 dB,驻波系数小于1.25。同轴转弯波导内部无介质支撑,且体积小,结构简单,易于实现,适用于高功率微波馈线系统中的同轴波导的转弯和连接。     

Sinusoidal modulation of a CW GaAs laser from 9 MHz to 1.1 GHz

Sinusoidal modulation and its detection of a room-temperature cw GaAs laser from 9 Mhz to 1.1 GHz is reported. A 25 dB signal-to-noise ratio with 20 dB harmonic rejection is obtained at 35 mA bias above threshold with a useful power output for optical fibre measurements. Possible extension of the frequency range and the application to sweep-frequency measurements in optical fibre waveguides are discussed.     

Experimental study of acoustooptical interaction in lithium niobate in the frequency range from 7.5 to 10.5 GHz

Results of the studies of acoustooptical interaction in a lithium niobate crystal upon excitation of an elastic wave in the direction of the X-axis by a multielement piezoelectric transducer at frequencies about 10 GHz are presented. The experimental method is described. Frequency dependences of the diffracted light intensity and acoustic damping as well as the frequency resolving power are studied. Damping of longitudinal acoustic waves in X-cut lithium niobate is measured to be 1.05±0.02 dB/cm GHz. The maximum diffraction efficiency reached 1% for 1 W of electromagnetic power supplied. The frequency bandwidths at the levels of 3 and 6 dB of the maximum value are 2.5 and 3 GHz, respectively. The frequency resolution is 15 MHz at the frequency of 9 GHz.     

衰减匹配的超声Barker码激励方法

为增加超声穿透高声衰减介质的能力,提出了一种衰减匹配的超声Barker码激励方法。基于换能器高斯响应与材料非频散线性衰减的假设,得到了Barker码激励的信号模型,求解旁瓣抑制滤波后脉冲压缩的信噪比表达式可知,该方法仅需要根据材料衰减特性与轴向分辨率的要求,分别调整Barker码的中心频率与时长,便可以获得更高的信噪比。取衰减系数为1.4 Np/(MHz·cm)、厚度为5 cm的橡胶为试样进行验证。当与方波激励方法的轴向分辨率相近时,衰减匹配的Barker码激励方法比传统Barker码激励方法的信噪比增益提高接近5 dB;当牺牲一定轴向分辨率时,信噪比增益提高接近11 dB。结果表明,衰减匹配的Barker码激励方法可以降低依频率衰减对脉冲压缩的影响,有效提高衰减回波的信噪比。      

分布损耗加载回旋行波管多模稳态注波互作用理论与比较证实

基于目前国际上实验研究的均匀介质加载和周期介质加载结构,建立了一种分布式损耗加载回旋行波管(gyro-TWT)多模稳态注波互作用理论.利用这一理论,以TE01模式基波gyro-TWT注波互作用为例,将Ka和W波段的理论结果与实验和软件仿真进行比较,以证实理论的合理性.     

Prediction and Measurement of Electron Density and Collision Frequency in a Weakly Ionised Pine Fire

Pine litter flame is a weakly ionised medium. Electron-neutral collisions are a dominant form of particle interaction in the flame. Assuming flame electrons to be in thermal equilibrium with neutrals and average electron-neutral collision frequency to be much higher than the plasma frequency, the propagation of microwaves through the flame is predicted to suffer signal intensity loss. A controlled fire burner was constructed where various natural vegetation species could be used as fuel. The burner was equipped with thermocouples and used as a cavity for microwaves with a laboratory quality network analyzer to measure wave attenuation. Electron density and collision frequency were then calculated from the measured attenuation. The parameters are important for numerical prediction of electromagnetic wave propagation in wildfire environments. A controlled pine litter fire with a maximum flame temperature of 1080 K was set in the burner and microwaves (8–10.5 GHz) were caused to propagate through the flame. A microwave signal loss of 1.6–5.8 dB was measured within the frequency range. Based on the measured attenuation, electron density and electron-neutral collision frequency in pine fire were calculated to range from 0.51–1.35 × 10¹⁶ m⁻³ and 3.43–5.97 × 10¹⁰ s⁻¹ respectively.     

220 GHz 折叠波导慢波结构

 优化设计了一种220 GHz的折叠波导慢波结构的尺寸,对其冷测特性如色散、耦合阻抗和衰减进行了分析。理论分析和软件仿真结果表明设计的折叠波导慢波结构在中心频率处具有较平缓的色散关系,较高的耦合阻抗和较低的电路衰减。互作用模拟表明,在电子注电压为20 kV,电流为10 mA时,27 mm（50个周期）的折叠波导慢波结构在220 GHz具有14.5 dB的增益,3 dB带宽为16.3 GHz（211.9～228.2 GHz）。     

A novel-configuration multi-wavelength Brillouin erbium fiber laser and its application in switchable high-frequency microwave generation

A novel configuration of compound-cavity multi-wavelength Brillouin erbium fiber laser is proposed and experimentally demonstrated. With an incident optical carrier power of 8 dBm, at least 14 lasing lines are obtained with a wavelength spacing of ∼0.08 nm. Stability and power uniformity of the multi-wave-length lasing are ensured by the flat hybrid gain of Brillouin and erbium, the compound-cavity structure, and the four-wave mixing suppression using a long (10 km) single-mode fiber. A stable and frequency-switchable microwave can be achieved by incorporating a fiber Bragg grating filter to select the desired nth-order Stokes wave and beating it with the optical carrier at a photodetector. In our experiment, the 1st-4th-order Stokes waves are filtered respectively and hence a high-quality microwave with a switchable frequency from ∼10 to ∼40 GHz and a tuning step of ∼10 GHz is achieved. The signal-to-noise ratio is measured to be >25 dB.