A method to predict multipath effects on a line-of-sight link

A method that computes the quality of a digital microwave line-of-sight link affected by multipath propagation is presented. The use of a statistical propagation model and of the signature concept allows the propagation effects to be separated from the characteristics of the equipment. Since the variations of the statistical mode coefficients with respect to the characteristics of the link under consideration are not known, experimental results have been achieved using assumptions based on physical considerations. A single channel is considered and the same principles, although more speculative because of the lack of data, are applied to a diversity channel     

Characteristics of double-groove guide at 3 mm wavelength

A groove guide having two parallel grooves may simultaneously propagate two modes with a small difference in phase constant. Experimental measurement of this difference for three groove separations at 100 GHz gives results close to theoretical predictions. The attenuation of one mode is a little less than for a guide with a single groove.     

Groove guide propagation characteristics at 3mm wavelength

Measurements of moding characteristics and attenuation on groove guide with appropriate dimensions for 3 mm wavelength operation show that it can be made with convenient dimensions, can operate with only the single dominant mode, and have a loss less than 1 dB/m.     

Amplitude and phase scintillation measurements on 8.2 km line-of-sight path at 30 GHz

The letter summarises results of amplitude and phase scintillation measurements at 30 GHz on an 8.2 km line-of-sight path in the Netherlands. The measured results compare favourably with those obtained from weak-scattering theory.     

Depolarization at 11.6 GHz on a terrestrial radio link

This paper presents some early data from an 11.6 GHz, 18 km terrestrial radio link operating in circular, linear horizontal and vertical polarizations. Rain, snow and clear weather effects are presented and analysed together with cumulative statistics over a fourteen month period. Observations indicate that rain depolarization is most severe on the circularly polarized transmission followed in order of magnitude by horizontal and vertical polarizations. Linear polarizations usage on a practical microwave link appears to be limited primarily by clear weathereffects. A good agreement with theoretical models for rainfall is obtained on circular and linear polarizations. During snow the variability of effects precludes a definitive classification of this type of precipitation, however, circular polarization exhibits a marked sensitivity to depolarization, generally less than that for the same rain attenuation level. The attenuation experienced during snow can be markedly different from event to event.     

Probability distribution of amplitude scintillations on a line-of-sight link at 36 GHz and 55 GHz

The probability distributions of the amplitude scintillations on 36 GHz and 55 GHz millimetre wave links along a 4.1 km path across central London have been obtained. These show that the log-normal distribution applies for the case of 36 GHz, but for 55 GHz, on the side of the oxygen absorption peak, the distribution departs significantly from log-normal.     

A comparative study of scintillation analysis over two line-of-sight paths at 6.7 GHz and 7.6 GHz

A comparison of the signal intensity fluctuations or scintillation of signal level, observed over two line-of-sight links is presented. These links are situated over Calcutta, DumDum-Andul (6.7 GHz) and Delhi, Delhi-Sonepat (7.6 GHz). The study reveals departures, in the occurrence and variation of the scintillation over the Calcutta path as compared with the path over Delhi. This deviation has been attributed to the large variation in humidity which exists in the coastal region, and also which plays a major role in microwave propagation in the troposphere.     

The effect of the outer scale of turbulence and wavelength on scintillation fading at millimeter wavelengths

Amplitude scintillation measurements made on two-millimeter microwave links at 36 GHz and 110 GHz along a common 4.1 km path across central London are deseribed. The variances of the logarithmic amplitude scintilliations at these two frequencies are compared for different ranges of the outer scale of turbulence. A comparison is made between the experimental results and the theoretical predictions of Tatarski. Good agreement has been found for the two cases when the outer scale of turbulence is greater than and smaller than the Fresnel zone size.     

Orotron with a two-row periodic structure at a wavelength of 1.3 mm with a wide electron beam

A discrete nonlinear theory is used to optimize the efficiency and output power of orotron at a wavelength of 1.3 mm. The device works at the first spatial harmonic of the two-row periodic structure (TRPS) with an increase in the width of electron beam. The dependence of the optimal length of TRPS at which the maximum efficiency is reached for a plane electron beam with a width of three radii of caustic on the plane mirror of the open resonator on the ohmic loss in the TRPS is obtained.     

Sunrise and sunset effects as observed on microwave propagation over a line-of-sight path

Microwave signal propagation provides an effective measure of studying the variable nature of the atmosphere. Sunrise and sunset periods are characterized by the dissolution and formation of nighttime temperature inversions. Signal amplitude recordings at 6.7 GHz over DumDum-Andul line-of-sight (LOS) communication link during post-sunrise period are characterized by the appearance of an enhancement in signal strength (as high as 20 dB). The sunset effect or the evening transition is observed as an enhancement in signal amplitude of about 10- 12 dB over the link. The signal characteristics observed during transition periods over the 6.7 GHz DumDum-Andul link are studied herein.     

Performance of a cryogenic 3 mm Schottky-mixer receiver on the Mets?hovi 14 m radio telescope

A cooled receiver with some novel features and a noise temperature of 80?140 K double sideband in the frequency range 75?95 GHz has been built for radio astronomical observations. The quasioptical beam switch is followed by a 3 mm Schottky mixer and FET amplifier at 1.4 GHz. For calibration the receiver is provided with a cold reference load within the Dewar.     

Large anomalous dispersion at short wavelength and modal properties of a photonic crystal fiber with large air holes

We investigated the dispersion and modal properties of a photonic crystal fiber (PCF) with larger air holes (LAH). The theoretical and numerical results show that large anomalous group-velocity dispersion at short wavelength down to around 700 /spl sim/ 800 nm can be achieved in a LAH-PCF with small pitch. Furthermore, the high-order modes usually are excited in a LAH-PCF when the optical field is launched from a traditional single-mode fiber, and all the excited modes will interfere when they propagate along the PCF. Finally, the properties of the excited modal spectrum and the multimode interference are determined by the normalized pitch and the normalized hole size of the PCF. All of these will provide references for the smoothing applications of the LAH-PCF.     

中短波红外双带通低温滤光片的设计与制备

双带通滤光片可以在元件的任意一个几何位置上同时透过两个光谱通道,从而实现双光谱通道的同时探测。文中研制了一种在100 K低温下使用的短波和中波红外双带通滤光片,选用Ge和SiO分别作为高低折射率膜层,在蓝宝石（Al₂O₃）基片上设计了具有Fabre-Perot(F-P)结构的短波通道滤光膜系和中波通道滤光膜系,它们在另一通带位置兼具增透能力,组合形成了包含短波通道(2.60~2.85 μm)和中波通道(4.10~4.40 μm)的双带通滤光片。Ge和SiO薄膜分别以电子束和电阻热蒸发的方式在高真空环境中完成沉积。测试结果显示,在100 K低温下,短波和中波通道的平均透射率分别达到91.2%和87.7%,顶部波纹幅度分别为2.1%和3.8%,波长3.00~3.95 μm光谱区域内的截止深度低于0.1%。该双带通滤光片在低温下的光学性能满足光学成像仪器的光谱应用要求,有利于更加精确的红外遥感和探测。     

Simulation of the effects of atmospheric scintillation on digital transmissions at centimeter and millimeter wavelengths

This paper describes the simulation of the effects of scintillation on digital transmissions. The scintillation is modelled by atmospheric turbulent cells whose parameters are determined by comparison with measured scintillation events. The effects of the cells crossing the communication link on the amplitude of the received signal are calculated as well as the transfer function. A complete communication link is simulated and the BER is calculated for different frequencies. The model can be used up to 100 GHz but this paper is focused on frequencies presently used in satellite communications.     

Study of backscattering from a complex scatterer at 3mm wave band

The backscattering characteristics of complex scatterer has been studied theoretically at 3 mm wavelength for the first time. RCS of the practial complex scatterer was calculated with GTD and the physical optics. The constrict model was also measured. The experimental results are in agreement with the theoretical calculations.     

All-optical wavelength conversion of short pulses and NRZ signalsbased on a nonlinear optical loop mirror

Wavelength conversion of short pulses at 10 GHz based on a nonlinear optical loop mirror (NOLM) is experimentally and numerically investigated for the case of small group velocity dispersion and walkoff between the control pulses and continuous lightwaves. Experimental and numerical simulation results show that the pulsewidths of the converted signals at different wavelengths are almost the same, and the pulsewidths are compressed when the peak power of the control pulse is smaller than a certain value. An RZ optical source containing eight wavelengths having a high sidemode suppression ratio, equal amplitudes and almost the same pulsewidths is obtained by using wavelength conversion in a NOLM consisting of a common dispersion shifted fiber. 10 Gb/s NRZ wavelength conversion based on the NOLM is demonstrated for the first time and certain conclusions in some of the references are confirmed by our experimental results     

基于偏振调制的最优接收灵敏度的ROF链路研究

提出了一个基于偏振调制的最佳接收灵敏度ROF链路系统。其根本原理在于实现具有最佳光载波边带比(OCSR)的光单边带调制技术,为此,利用偏振调制和滤波技术,线偏光首先经由一个特定偏振角进入偏振调制器,然后一个固定起偏角的起偏器被用来合并偏振信息,最后利用一个光滤波器实现光双边带调制到光单边带调制的转换。研究发现所获得的OCSR只与两个偏振角(和)有关,通过仔细调节上述指标,可以将OCSR调谐至最佳值0 dB。利用仿真验证了上述结论,仿真发现通过将OCSR调谐至最佳值将大大提高ROF链路的接收灵敏度。     

Optimization of orotron with two-row periodic structure at a wavelength of 1.3 mm in the framework of an approximate analytical theory

An approximate analytical theory is employed to optimize the parameters of an orotron with a two-row periodic structure (TRPS) and a semispherical open resonator at a wavelength of 1.3 mm. The TRPS period and length are chosen using the experimental verification of the optimization results. The optimization is performed for TRPS periods of 0.29 and 0.25 mm and mismatch parameter of b = 0.05. Under certain conditions, the output power of the orotron with TRPS at a wavelength of 1.3 mm may amount to tens of watts.     

3mm波段天空亮温计算与测量

在毫米波被动探测中,金属目标往往是被探测的对象.金属的发射率近似为零,它几乎全部反射来自天空的辐射能量.建立了晴天时的天空亮温计算模型,在3mm波段计算了天空亮温.在几种典型天气条件(晴天、多云、阴天、降雨)下对天空亮温进行了实验测量.测量结果表明,晴天时的天空亮温计算模型是可行的,天空亮温随天气条件而变.晴天时,随着温度和湿度的增加,天空亮温明显增大;晴天淡云对天空亮温的影响较小;阴天时的浓云层对天空亮温的影响显著;降雨对天空亮温的影响最大.