Multiple scattering effects on wave propagation due to rain

At frequencies below 10 GHz, the scattering crosssection of raindrops is small compared with the absorption cross-section and the multiple scattering effect is negligibly small. At higher frequencies, however, the scattering cross-section becomes comparable to the absorption cross-section, and some multiple scattering effects may be observed. This paper presents a study of the multiple scattering effects, and the resulting incoherent intensity for a plane wave incident upon a plane-parallel rain region. General formulations of the equation of transfer using Stokes’parameters are given, and the extinction matrix is introduced which take into account the depolarization effects and the nonspherical shape of raindroplets. The calculations are made for the spherical droplet case. It is assumed that a circularly-polarized wave is normally incident upon a plane-parallel rain medium. The scattering characteristics are calculated using the Mie solution and the Laws-Parsons distributions. The calculation of the incoherent intensities are made using the matrix eigenvalue technique. The exact solutions are compared with the first-order scattering solution to estimate the range of validity of the first-order theory. The ratio of the incoherent to the coherent received powers are calculated at 30 GHz, for rain rates of 12.5, 50, 100, and 150 mm/h, rain thicknesses of 3 km and 10 km, and fields-of-view of 1, 5, and 15 deg.     

Radio wave propagation through rain forests of India

A radio wave attenuation measurement survey program was undertaken for the tropical rain forests of India. Measurements were taken at frequencies from 50 to 800 MHz, for antenna heights from 1.5 to 16.5 m above the ground with both horizontally and vertically polarized emissions, and at various separation distances varying from 40 to 4000 m. There were 96 combinations of system parameters for each selected distance between transmitting and receiving locations. In addition to the copolar measurements, cross-polar measurements were carried out to study cross-polar phenomenon in the presence of vegetation. The results of the studies are discussed, covering scatter of the data, lack of homogeneity of the foliage, variation in foliage proximity of the antenna, scattering of radio waves, effect of antenna beamwidth, effect of changes in wind velocity, frequency and polarization dependence of the basic transmission loss, seasonal variation of the loss, effect of climate and type of vegetation, foliage loss, specific attenuation, and effect of increased antenna height in the forest. An empirical model derived from these measurements is proposed     

Measurements of 20-GHz transmission through a radome in rain

An experiment has been designed to study the effects of rain on transmission through large radomes of the type which may be used with ground station antennas in satellite links. Measured transmission data from the experiment are described and compared with predicted values. The nonwetting nature of the radome surface significantly degraded with time, and this was accompanied by a large increase in the 20-GHz transmission loss during periods of rain. The losses were in the range of 6-8 dB for rain rates of 3-40 mm/h. The cumulative distribution of transmission through the radome for a 12-month period is presented.     

19-GHz rain attenuation characteristics on four tandem links

Rain attenuation measurements of 19 GHz were made on four tandem links at Musashino district near Tokyo. This paper discusses the characteristics of rain fade probabilities on tandem links. A multiplicative factor which reduces the worst case estimate of adaptive probabilities developed. This factor increases (approaches 1) as the rain attenuation becomes deeper. The measured modification factor at a rain attenuation of 30 dB was about 0.81 on four tandem links, 0.82 on three tandem links, and 0.88 on two tandem links. It has a tendency to saturate with an increase in the number of links.     

Forward scattering due to rain at 11 GHz

Forward scattering from rain was measured at 11 GHz over a 9-km line-of-sight path. For rain rates of 100-150 mm/h, the scattered signal was observed to be about 40 dB below the direct signal. Good overall agreement was obtained between theory and experiment.     

Attenuation due to rain at low elevation angles

Radar data on the reflectivity structure of rain showers were analysed to determine the dependence on elevation angle of attenuation statistics at 13 GHz on satellite propagation paths. For elevation angles between 10° and 30°, It was found that the attenuation occurring at a given probability level varied approximately with the cosecant of the elevation angle. For elevation angles below 10°, it was found that the frequency of occurrence of a given attenuation varied approximately with the cotangent of the elevation angle.     

Statistical variations in forward propagation rain depolarization due to drop size fluctuations

Observed electromagnetic wave depolarization in forward propagation due to precipitation tends to distribute statistically about some mean level of depolarization. This is due to random rain parameters that cause this depolarization. Using a drop-size modified depolarization model, we have analyzed the statistical scatter of the cross polarization ratio due to random distributions of drop population and size and found a standard deviation of approximately 2.5 dB about the mean, independent of frequency.     

典型场景下电波传播特性建模

为了解决某些典型场景(如海上、山区、丘陵、城区)下无法使用已有基础模型来全面表达电波传播特性的问题,建立了一种在典型场景下,基于确定性抛物方程、适用于多个传输场景的统一电波传播模型。把典型场景等效为损耗介质层来求解边界条件,利用Fourier分步步进法得到相应解,然后得到电波在典型场景下的传播损耗,并进行了理论分析和实验验证。结果表明,在不同传输场景下,将统一电波传播模型与Miller-Brown模型、射线追踪模型进行比较,结果较吻合,验证了其正确性。这一结果对建立一种求解典型场景下电波传播衰落问题的统一电波传播模型是有帮助的。     

C波段蒸发波导传播衰落特征的试验研究

海洋蒸发波导是海上超视距传播的主要机制，对于海上无线电系统的设计和运行具有重要影响.利用在我国南海开展的蒸发波导环境下的C波段微波超视距传播试验数据，对比分析了不同传播距离下的路径损耗和信号快衰落分布特征.试验结果表明:随着传播距离的增大，路径损耗逐渐接近对流层散射传播损耗，主要传播机制也逐渐从蒸发波导传播向对流层散射传播过渡；5 min采样的接收信号电平快衰落分布接近为广义瑞利分布，衰落深度和衰落幅度均小于瑞利分布.所得结果对利用蒸发波导的通信系统设计具有参考价值.     

Phase and amplitude dispersion for Earth-satellite propagation in the 20- to 30-GHz frequency range

Amplitude and phase dispersion have been measured for over a year on a 19- and 28-GHz earth-space propagation path. In the experiment amplitude and phase differences were compared for a 28-GHz carrier withpm264-MHz sidebands and a 19-GHz carrier, all transmitted from a COMSTAR satellite. No dispersion (frequency selective fading) was found of the type caused by multipath propagation with a large spread in time delay or by resonances in the propagation medium. The only frequency dependences evident were due to the bulk properties of water in rain. The conclusion from this investigation is that amplitude and phase dispersion should not pose a problem for wideband (on the order of 1 GHz) satellite communication systems operating at frequencies greater than 10 GHz with elevation angles from the earth terminals of greater than15deg.     

Radio propagation within buildings at 900 MHz

The letter reports some results of a survey which studied the propagation of radio signals at 900 MHz within buildings for the operation of cordless telephones. Histograms are presented of signal strength together with computed values for bit-error ratio for digital FSK modulation. A distance/power law is derived appertaining to the propagation characteristics of the building.     

Cross polarization at 18 and 30 GHz due to rain

Analysis indicates that the canting angles of freely falling raindrops are of great importance in determining the magnitude of the cross polarization in higher frequency (18-30 GHz) radio relay systems. Since knowledge of these canting angles is sparse, the images of 463 raindrops obtained with a raindrop camera by personnel at the Illinois State Water Survey have been measured to obtain the distribution of canting angles during two rainstorms. The distributions for both storms are similar, with 40 percent of the drops having positive canting angles exceeding15degwith respect to the horizontal, and 25 percent having negative angles of less than-15deg. Calculations based on the measured distributions and representing upper bounds indicate that a relay system at both 18 and 30 GHz and with a repeater spacing of 3.5 km will experience cross polarization less than -20 dB at rain rates of 150 mm/hr.     

Radio propagation characteristics for line-of-sight microcellularand personal communications

To acquire a knowledge of radio propagation characteristics in the microcellular environments for personal communications services (PCS), a comprehensive measurement program was conducted by Telesis Technologies Laboratory (TTL) in the San Francisco Bay area using three base station antenna heights of 3.2 m, 8.7 m, and 13.4 m and two frequencies at 900 MHz and 1900 MHz. Five test settings were chosen in urban, suburban, and rural areas in order to study propagation in a variety of environments. This paper reports the LOS measurements in different environments, all of which show variations of signal strength with distance that have distinct near and far regions separated by a break point. It was also found that the location of the break point for different frequencies and antenna heights can be calculated based on first Fresnel zone clearance. The regression analysis reveals a slope that is less than two before the break point, while it is greater than two after the break point. This break distance can be used to define the size of microcell and to design for fast hand-off. Beyond the first Fresnel zone break distance the base station antenna height gain was observed to approximately follow the square power law of antenna height     

Radio propagation characteristics in underground streets crowdedwith pedestrians

Radio propagation characteristics in an underground street crowded with pedestrians are presented. Measurements were carried out on vertical and horizontal polarization characteristics in a frequency range from 250 MHz to 12.4 GHz. In the analysis, the region with pedestrians is modeled as a lossy, homogeneous dielectric slab. Based on the method of effective dielectric constant, some numerical results are presented for the attenuation constant and for the field distribution in the cross section and are compared with experimental data. It is shown that the method is applicable in determining the propagation characteristics in underground streets crowded with pedestrians     

Italsat-Olympus 20-GHz orbital diversity experiment at Spino d'Adda

This paper reports results of the 20 GHz orbital diversity experiment between the geostationary satellites Olympus (19°W) and Italsat (13°E), as viewed from Spino d'Adda, Po Valley, northern Italy. The results show that: (a) the statistical gain is significant; and (b) for a small angular separation in the geostationary orbit between the satellites (32° in our experiment) the gain, normalized to single link attenuation and expressed in percent, is, as a rule of thumb, of the order of magnitude of this angle expressed in degrees, 30% in our experiment     

Radio wave propagation loss in the VHF to microwave region due tovehicles in tunnels

An experiment was undertaken to determine how obstacles in tunnels affect microwave propagation loss. The major emphasis of the study was on determining the propagation loss due to the following parameters: number, location, and size of vehicles, and cross-sectional shapes of tunnels. The laboratory experiments was performed using tunnel models with arched and rectangular cross sections. The dominant mode was transmitted into these tunnels from entrances. Different readings of field strength were taken along the length of the tunnels to determine the effect that vehicles can have on the propagation characteristics. The scale ratio of the tunnel dimensions to the wavelength is about 2-3. It is shown that the basic propagation loss due to vehicles in tunnels is determined mainly by the number and the size of the vehicles. Vehicle location and tunnel cross-sectional shape do not affect the propagation loss significantly     

Microwave attenuation due to rain at 110 GHz in south-east England

Fading due to precipitation has been recorded at 110 GHz for a period of one year over a 2.65 km path near Slough, England. The results show that frequencies as high as this could be used for relay links over short distances with acceptable reliability, despite the large attenuation due to heavy rain.     

High-speed ASK transceiver based on the NRD-guide technology at60-GHz band

A new type of high-speed amplitude shift-keying (ASK) transceiver has been developed in an integrated manner at 60 GHz by using the nonradiative dielectric waveguide (NRD-guide) technology. An emphasis is placed on the high-speed performance of the newly developed ASK modulator. The modulator uses a Schottky barrier diode (SBD), which has higher switching speed than a p-i-n diode. In addition, the operation principle of it is different from that of the conventional p-i-n diode modulator. A pair of NRD-guide transceivers have been fabricated and 400-Mb/s data-transmission test has been carried out successfully by using them