The dynamics of rain-induced fades

The dynamics of rain-induced fades on radio links is studied by evaluating the rate at which the first Fresnel zone volume fills with rain. The amount of water in this volume determines the fade depth, and the rate at which it fills establishes the fade slope. A compact expression for fade slope on a terrestrial path is derived. This expression shows that once the rain rate is specified, fade slope is very sensitive to differences in rain velocity. Thus, there is no unique relationship between fade slope and rain rate     

Depolarisation due to snow at 11.6 GHz

Depolarisation events due to snow covering a period of three years on an 11.6 GHz, 18 km link employing linear and circular polarisation are presented. These are used to demonstrate the variability of wet and dry hydrometeor scattering. By deriving the equivalent differential phase-shift from the measurements it is possible to show the relative importance of differential phase and amplitude effects in depolarisation for the different hydrometeors.     

Site-diversity advantage for satellite communication at 11.6 GHz

Two ground stations, used as a site-diversity pair, can substantially reduce the duration of fades on satellite links operating at frequencies about 10 GHz. Changes in sky-noise temperature during severe summer rainstorms have been measured simultaneously by five spaced 11.6 GHz radiometers in SE England, and these observations are used to derive the signal fading that would have occurred on a satellite communication link. The results show that a tenfold reduction in the duration of fades exceeding 3 dB can be obtained by switching between a pair of sites spaced 5 km apart along a line perpendicular to the viewing direction. For fades deeper than 6 dB, the same improvement occurs at a spacing of only 2 km.     

Broadband cryogenic parametric amplifier operating at 11.6 GHz

A machine-cooled cryogenic parametric amplifier that operates at 20 K is described. The 2-stage amplifier has a 0.5 dB bandwidth of 600 MHz at 20 dB gain and an effective input noise temperature in the range 47?51 K over the frequency band of 11.3 to 11.9 GHz     

Radiometric rain attenuation measurements at 11.6 GHz in Peru

Rain attenuation is one of the key design parameters when setting up satellite communications systems at frequencies above 10 GHz. Reliable and economical system design requires fairly accurate estimates of this parameter. Although rain attenuation prediction models are available for temperate climates, little has been reported for tropical regions where rain impairments can be very much more severe. This letter presents radiometrically determined rain attenuation results at 11.6 GHz in a tropical climate.<>     

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.     

Frequency scaling of rain-induced attenuation at 11, 18 and 30 GHz

Frequency scaling makes it possible to derive rain induced attenuation statistics at higher frequencies on the basis of the available data obtained at lower frequencies. Attenuation data are simultaneously obtained at 11,18 and 30 GHz on the same terrestrial 10 km path. Experimental results are compared with those obtained by various prediction methods and, in many cases, the concordance is quite satisfactory.     

Attenuation statistics at 11.6 GHz from satellite SIRIO after three years' activity in Italy

Rain attenuation statistics based on SIRIO data at 11.6 GHz collected in three Italian stations are presented. The long-term probability distribution can be excellently fitted by a power law up to a 9 dB attenuation level.     

Depolarization measurements at 11.6 GHz on Earth-space paths using the SIRIO satellite

Depolarization (XPD) data at 11.6 GHz in circular polarization collected during the SIRIO experiment on the Italian stations of Fucino and Lario are presented and analyzed. The obtained results are presented both in conditional form (i.e., XPD statistics conditioned to the co-polar attenuation (CPA)) and in "equiprobable" form (i.e., by comparing XPD-CPA values exceeded for the same fraction of the total observation time). The conditional XPD appears spread in an interval ofpm5dB around the conditional median value. This latter appears to be very close to the "equiprobable" value. The International Radio Consultative Committee (CCIR) procedure giving the "equiprobable" XPD appears fairly well supported by the Fucino data, while the Lario data give higher depolarization than predicted by CCIR.     

High values of rain-induced differential attenuation measured on a 53 km path at 13 GHz

An experiment was designed to determine the differential attenuation due to rain at 13 GHz on a 53 km path. Differential attenuations measured during the summer of 1975 are higher then those predicted by theory or reported by other experimenters.     

Measurement of rain-induced zenith-path attenuation using 19.9 GHz radiometer at Amritsar (India)

The paper presents the results of 19.9 GHz radiometric propagation studies conducted over a period of one year at Amritsar, for determining rain-induced zenith path attenuation. The zenith path attenuation has been determined by the measurements of sky noise temperature received by the radiometer. The results obtained from the experiment are presented in the form of annual cumulative distributions of rain rate, sky noise temperature, and zenith path attenuation together with worst-month statistics. The rainfall rate cumulative distribution as predicted by ITU-R for our geographical location is lower than the actually measured rainfall rate cumulative distribution. The cumulative distribution of zenith path attenuation predicted by using ITU-R model overestimates the measured cumulative distribution of zenith path attenuation.     

Joint analysis of duration and rate of change of rain attenuation at 11.6 GHz

Positive and negative rates of change of attenuation are studied jointly with the in-between fade duration using Sirio 11.6 GHz beacon four-year data for several attenuation thresholds, collected in northern Italy. The letter shows that the rate conditional distributions are log-normal, and that little correlation exists between negative and positive rates and durations.     

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.     

Diurnal distribution of rain attenuation in communication andbroadcasting satellite systems at 11.6 GHz in Italy

The paper presents long term probability distributions of rain attenuation exceeded in 0.5-h, 1-h, 2-h, 4-h, 8-h, 12-h and 24-h contiguous periods of the day, at 11.6 GHz, circular polarization, in satellite radio links, at two sites in Italy (Gera Lario and Fucino). These data can be useful to match the system design to the time of the day, which can be affected very differently by rain attenuation. The results can be scaled to higher frequencies and are directly applicable to actual satellite TV and radio broadcasting, and to telecommunication systems in the 12 GHz band. The data have been obtained by applying the synthetic storm technique (after testing its predictions in the 4-h case against experimental long term results) to a large and statistical reliable set of rain rate time series collected in five years (1978-1982) of continuous observation during the satellite SIRIO experiment, in slant paths of elevation angles 32° and 33°. The number of concurrent rain rate (and rain attenuation) time series considered is 587 for Gera Lario and 562 for Fucino, a very large data bank     

Results of 11.6 GHz radiometric experiment in Nigeria: second year

Three experiments were set up within a joint African radiometric propagation measurement program to provide data at frequencies above 10 GHz for predictive modelling. The authors report the results of the second year of measurements in Ile-Ife, Nigeria. Compared with ITU-R (formerly CCIR) predictions, the rain measurements agree fairly well but the path attenuation results differ significantly     

Ice depolarization of the COMSTAR beacon at 28.56 GHz during low fades and correlation with radar backscatter

Radar correlation with significant ice depolarization events accompanied by low copolarization fades of the 28.56-GHz COMSTAR beacon signal are described for an experimental program at Wallops Island, VA. Using a Faraday switch at the front end of the receiver, the copolarization and cross-polarization levels of the 28.56-GHz beacon signal are sequentially monitored. A nearby high resolutionS-band radar pointing along the Earth-satellite path monitors the simultaneous ice and rain reflectivity. Excellent correlation is noted between the cross-polarization events and relatively large and extended ice reflectivities along a segment of the Earth-satellite path at altitudes near and above the 0°C isotherm. The radar and receiver data strongly suggest the cross-polarization mechanism is due to a hailshaft which intersects the path at altitudes well below the 0° isotherm. Since the intervening ice results in a cross-polarization signal which either adds or subtracts to the cross-polarization antenna residual, a method is described to remove the residual from the resultant measured cross-polarization level, without employing a phase measurement. Cumulative, month-of-year and time-of-day statistics associated with the depolarization signals are established.     

Observations of troposcatter and anomalous propagation signallevels at 11.6 GHz on 155 km path over the sea

Microwave CW transmissions from the French coast near Le Havre are being monitored at Portsmouth along a 155 km path. Preliminary observations indicate that the troposcatter levels of about -117 dBm agree with conventional calculations. However ducting has been seen to persist for long periods, with signal levels exceeding the free space value of -48 dBm by several decibels. On other occasions enhancements of several tens of decibels have been associated with warm and cold fronts and with heavy rain     

Results of 11.6 GHz radiometric experiment in Kenya: second year

Three experiments were set up within a joint African radiometric propagation measurement program to provide data at frequencies above 10 GHz for predictive modelling. The authors report the results of the second year of measurements in Nairobi, Kenya, along with mean results for the two years. Significant differences are evident between the measured results and the ITU-R (formerly CCIR) rain zone and path attenuation predictions     

Results of 11.6 GHz radiometric experiment in Cameroon: second year

Three experiments were set up within a joint African radiometric propagation measurement program to provide data at frequencies above 10 GHz for predictive modelling. The authors report the results of the second year of measurements in Douala, Cameroon, along with mean results for the two years. These show significant departures from the ITU-R (formerly CCIR) rain climate and path attenuation models     

A comparison of copolar and cochannel satellite interference prediction models with experimental results at 11.6 and 20 GHz

One of the main propagation effects on interference between adjacent Earth–space paths is the differential rain attenuation. In the present paper, two existing copolar and cochannel satellite interference prediction models are compared with experimental data of this kind, derived from radar or attenuation measurements. The comparison shows a quite satisfactory agreement and this combined with the fact that the data refer to satellites quite displaced in the geostationary orbit leads to the following conclusion: the predictive models under consideration can be used not only for fixed satellite systems but also for mobile systems using general antennas with low gains. Copyright © 2000 John Wiley & Sons, Ltd.