Attenuation caused by rain at frequencies above 10 GHz

Measurements of the attenuation caused by rain have been performed on a 20 km test path at frequencies of 12, 15, 19, 29 and 39 GHz. Simultaneously the rain intensity has been measured with ten rain gauges installed along the path so that the average spacing of the rain gauges is about 2 km. For a oneyear period the results of the rain gauge network were used to determine the statistical distribution of the pointrain intensity, and the path averaged and timeaveraged rain intensities. Comparisons were made between the experimental rain attenuation and the attenuation calculated from the measured rain intensities using Miescatter theory. In nearly all cases good agreement was obtained. Using the pointrain rate distribution, the prediction method of S. H. Lin for rain attenuation statistics was tested.     

Theoretical random process for prediction of rain attenuation statistics in site diversity satellite links above 10 GHz

Site diversity systems are foreseen for earth-to-satellite links in localities with high rain-induced attenuation operating at frequencies above 10 GHz. An analytical model for the rain-rate statistical process is developed using radar-derived information on the rain structure collected at Spino d'Adda in the framework of the Sirio experiment. The procedure for estimating rain attenuation in both single and site diversity systems is outlined in a general formulation which makes it applicable to different situations. The model gives results very similar to experimental ones.     

Simple rain attenuation prediction method for satellite radio links

The desirable features of a rain attenuation prediction method to be used in satellite radio link engineering are established, and a method satisfying such features is proposed. The method is tested over 77 satellite links situated in Europe, the USA, Japan, and Australia. Comparisons are made with the International Radio Consultative Committee (CCIR) method (CCIR, vol.V, Report 564, XVI Plenary Assembly, Dubrovnik, 1986). Using the worldwide coefficients for the links located in Australia there results a marked overestimation and a poor accuracy. This situation does not occur for the links located in Europe, the USA, and Japan, which are in temperate climates. The method's limitation is related to low rain intensities in satellite links having low elevation angle     

The relationship of rain-induced cross-polarization discrimination to attenuation for 10 to 30 GHz earth-space radio links

Rain depolarization is quantified through the cross-polarization discrimination (XPD) versus attenuation relationship. Such a relationship is derived by curve fitting to a rigorous theoretical model (the multiple scattering model) to determine the variation of the parameters involved. This simple isolation model (SIM) is compared to data from several earth-space link experiments and to three other models.     

Model for estimating rain attenuation at frequencies in range 6-30GHz

The raindrop size distribution (RSD) for various types of rainfall over Guwahti, India is presented. The observed RSD parameters are compared with those given by other models. By employing the observed RSD, the values of a and b in the relation A=aR^b for estimating the rain attenuation at frequencies from 6 to 30 GHz are given. The significance of the type of rainfall in controlling attenuation is discussed     

Model of intense convective rain cells for estimating attenuation on terrestrial millimetric radio links

The movement of intense rain over a line of rapid-response rain gauges is shown to be related to the wind speed at the 700 mbar level. This relationship is used to deduce model rainfall intensity/distance profiles from intensity/time profiles recorded at a point. The model is applicable to the calculation of attenuation at frequencies above about 30 GHz.     

GaAs/GaAlAs heterojunction bipolar transistors with cutoff frequencies above 10 GHz

This paper describes the fabrication and high-frequency performance of an npn GaAs/GaAlAs heterojunction bipolar transistor. The fabrication process utilized molecular beam epitaxy, and featured a nominal base layer thickness of 500Å. The cutoff frequency,ft, of the transistor was measured to be 11 GHz (a value which was limited by parasitic elements associated with bonding pads and bond-wires).     

A method for predicting rain attenuation in terrestrial point-to-point line of sight links at 97 GHz

Rain attenuation caused by electromagnetic scattering and absorption is a major design parameter for setting up satellite communication systems operating at frequencies above 10 GHz. In this paper, a method for predicting rain attenuation in terrestrial point-to-point line of sight links at 97 GHz is proposed using previously available experimental data obtained in the south of UK over a period of more than a year. Rainfall rate and percentage of time are used as input data in the proposed prediction method. Results show that our prediction method based on artificial neural networks reveals very good agreement with the experimental data.     

Characterization of rain profiles in a second-order approximation and application to attenuation beyond 10 GHz

A new approach to characterizing the rain profile for applications involving attenuation beyond 10 GHz is presented. It is based on the use of three functionals of the rain intensity profile (referred to as "intrinsic profile parameters" because of their peculiarity of being independent of frequency) which encompasses all the relevant information contained in the profile itself with respect to the attenuation. The attenuation can then be evaluated without the need for any profile model, as happens when starting from the more usual "average rain intensity" or other similar meteorological parameters. The intrinsic parameters therefore allow for the separate accounting of the profile and the other factors affecting attenuation such as frequency, raindrop size distribution, etc. Moreover, they can be easily related to the various kinds of "effective rain intensity" and "rainy path length" defined in the literature, thus offering a tool to clean out the inherent dependence of these latter on frequency and to obtain results that are comparable among each other even though they are collected under different circumstances.     

Analysis of fading due to rain, snow and multipath propagation for 11 GHz radio links variously located in England

The propagation performance of six microwave links operating at frequencies near 11 GHz were monitored for the years 1973-75. Fades were classified as due to rain, snow or multipath (including other refractive effects). It was found that, on average, the contributions of each of the three types of fade to the total statistics were comparable, although there were considerable variations in the statistics, both from year to year and at different locations.     

Practical means of cancelling the differential phase contribution to rain crosspolarisation at 10 GHz and above

At certain frequencies, removal of the differential phase contribution to rain-induced microwave crosspolarisation may produce adequate crosstalk improvement in dual-polarised links. Rotating section polarisers are shown to be capable of this removal in the presence of differential attenuation, and one-parameter approximations to the operation are shown to exist.     

A new method for the prediction of fade duration statistics in satellite links above 10 GHz

A model for the statistical prediction of fade durations, applicable both to scintillation and rain-induced effects, is presented in this paper. It assumes that durations longer than about 1 minute are lognormally distributed whereas shorter durations follow a power-law distribution. The model is assessed using data contained in the CCIR data bank and from measurements performed with the SIRIO and Olympus satellites. The model is tested using the same data, and the results give multiplicative errors in the range from 0.6 to 1.8 (averages) and from 0.3 to 3.0 (r.m.s.) in the estimation of the fade durations exceeded for fixed probability.     

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.     

Improvement of a rain attenuation prediction method for terrestrial microwave links

An empirical model for predicting rain induced attenuation on terrestrial paths using effective path length is proposed. Comparison with the recently prediction method proposed by the International Radio Consultative Committee (CCIR) is made. It appears that our prediction method reveals good agreement with experimental data from different locations in the world.     

Worst-month rain attenuation and XPD statistics for satellite paths at 12 GHz

Worst-month attenuation and XPD data are presented from a three year measurement program at Blacksburg, Virginia USA using the SIRIO 11.6 GHz beacon. The ratio of worst month to annual percentage occurrence levels (Q) for the attenuation and XPD data agree closely with each other. They also show excellent agreement to the CCIR model. Comparisons to previously reported experimental results are also given.     

一种地面视距链路雨衰减预测模式

基于指数雨胞雨衰减物理模型得到的降雨率调整因子概念,通过对ITUR雨衰减数据库实验数据的分析,提出了一种降雨率调整因子公式,并利用ITUR雨衰减数据库数据回归得到了降雨率调整因子公式的参数,建立了一种利用全概率降雨分布的地面视距链路雨衰减预测模式通过与其它模式的比较表明：该模式预测精度优于其它利用全概率降雨的雨衰减预测模式,预测精度与利用概率转换的ITUR模式相当,且预测过程更加简便。     

Theoretical efficiency of the l.s.a. mode for gallium arsenide at frequencies above 10GHz

The efficiency of the l.s.a. mode is calculated for galliumarsenide diodes taking account of all the electron-lattice relaxation processes. The efficiency falls off with increasing frequency and typically becomes negative above 100GHz.     

Instantaneous frequency scaling of rain attenuation at 11.6-17.8 GHz with SIRIO data

The ratio of simultaneous attenuation measurements performed at 11.6 and 17.8 (or 17.0 GHz) with the Italian satellite SIRIO is discussed. The main application of this information is in the field of the "up-path power control" in earth-space telecommunication systems for which the requirement of estimating the uplink attenuation form measurements on the downlink will probably be taken into consideration as a tool to keep constant the total power received on board. The analysis shows that the average ratio between attenuations at 17.8 and 11.6 GHz, conditioned to the downlink attenuation (11.6 GHz) tends to decrease slightly with attenuation; it turns out to be very close to the ratio between equiprobable values of attenuation computed from the concurrent cumulative distributions (long-term frequency scaling ratio); the standard deviation is of the order of 10 percent of the average value and also exhibits some tendency to decrease; both the overall cumulative distributions and the conditional ones are well fitted by log-normal probability models with standard deviation (of the natural logarithm) constant and equal to 0.13-0.14 up to 5.5 dB in the downlink attenuation.     

An empirical formula for the prediction of rain attenuation infrequency range 0.6 - 100 GHz

An empirical formula for calculating the extinction cross section (ECS) by raindrops over a broad frequency range is first derived based on extensive calculations made on a widely varying in mean radius of modified Pruppacher and Pitter (MPP) raindrop models ranging from 0.25 to 3.5 mm. The expansion coefficients in the empirical formula are determined by least-squares curve fitting of numerical data obtained by the volume integral equation formulation (VIEF). The formula satisfies the frequency and raindrop size dependence. Numerical results obtained from the empirical formula for calculating the ECS are generally in good agreement with those calculated by the VIEF for raindrops with mean radius varying from 0.25 to 3.5 mm in the frequency range from 0.6 to 100 GHz. The average error in the ECS is less than 10%. The formula thus provides a simple and inexpensive method for calculating the ECS of raindrops, which otherwise requires complicated and expensive methods of calculation. By implementing this empirical formula of ECS into the rain attenuation equation, a new numerically empirical formula for calculating the specific rain attenuation is also proposed. The validity of the empirical formula for calculating the specific rain attenuation is also checked by comparing the obtained results of specific rain attenuation with those obtained from Li et al.'s (1995) solution, Yeo et al.'s (1993) measurement, and Olsen et al.'s (1978) power-law equation     

Comparison of antenna noise temperature with rain attenuation of a satellite beacon signal at 12 GHz

Simultaneous measurements of antenna noise temperature Ta and satellite beacon attenuation were made to examine the quantitative relation between them, and to determine the `apparent? effective medium temperature which provides an accurate estimate of slant-path attenuation. The correlation between the attenuation and the increase in Ta due to rain is very good, and the effective medium temperature derived from the `apparent? one is reasonably consistent with a theoretical result.