The multiple scattering by two parallel conducting circular cylinders is considered. The total scattered field is divided into two components, namely a noninteraction term and a term due to all interactions between the cylinders. The noninteraction term is expressed exactly, whereas the interaction field is evaluated using the method of moments. It is found that this technique leads to an efficient solution for both the monostatic and bistatic scattering by cylinders of large radii. The computational advantages of this technique over classical boundary value and numerical solutions are presented.

Scattering by parallel conducting circular cylinders

Rain attenuation at 355.2 GHz in the terahertz wave range was measured with our new 355.2 GHz measuring system under rainfall intensities up to 25 mm/hr. Rain attenuation coefficients were also calculated using four raindrop-size distributions, e Marshall-Palmer (M-P), Best, Polyakova-Shifrin (P-S) and Weibull distributions, and using a specific rain attenuation model for prediction methods recommended by ITU-R. Measurements of a terahertz wave taken at 355.2 GHz were compared with our calculations. Results showed that the propagation experiment was in very good agreement with a calculation from a specific attenuation model for use in prediction method recommended by ITU-R.

/pdf/measurement-of-rain-attenuation-in-terahertz-wave-range-2cs3ep6olw.pdf

Measurement of Rain Attenuation in Terahertz Wave Range

Network fade countermeasures for link budget can be better implemented based on the knowledge of seasonal variability of rainfall attenuation in a locality. Therefore, in this study, a seasonal approach is applied to estimate the efiects of spatial rainfall attenuation in Durban (29 - 52'S, 30 - 58'E), South Africa using two- year rainfall data obtained from the RD-80 Joss-Waldvogel (J-W) distrometer. An analysis is undertaken for difierent seasons to obtain the rainfall rate exceedences at 0.001%, 0.01%, 0.1% and 1% of time. Consequently, rainfall drop-size distribution (DSD) models are developed for the control site at difierent seasons for the same period. The probability density analysis for each model indicates that the lognormal distribution best flts the summer and autumn season with percentage root-mean-square errors (RMS) of 30% and 26% respectively; gamma distribution flts winter season with RMS error of 16% and Weibull distribution flts spring season with RMS error of 26%. The results from the rainfall rate and rainfall DSD are combined to estimate the rainfall speciflc attenuation, by applying spherical droplet assumption for Mie scattering techniques, between 2GHz and 1000GHz. With this, the seasonal k and fi coe-cients for speciflc attenuation are derived from the best rainfall DSD models, using regression technique at 2.5GHz, 25GHz, 40GHz and 100GHz. At these frequencies, the results show that the predicted speciflc attenuation coe-cients for all seasonal rainfall rates at the control site are lower, when compared to those from ITU-R models. It is concluded that speciflc attenuation levels may be similar and more intense in summer and autumn seasons, while, lower and less intense in autumn and winter seasons at similar rainfall rates.

/pdf/seasonal-analysis-and-prediction-of-rainfall-effects-in-preed59tid.pdf

Seasonal Analysis and Prediction of Rainfall Effects in Eastern South Africa at Microwave Frequencies

[1] The forward scattering amplitudes for the spherical raindrops are determined for all raindrop sizes at different frequencies by using the Mie scattering theory. The real parts of the extinction cross sections are used to generate power law models at different frequencies. These are integrated over different established raindrop-size distribution models to formulate rain attenuation models. Using the developed rain attenuation models with 5 year rain rate statistics at R0.01 determined in previous work, the specific rain attenuation is computed. The experimental results obtained from the horizontally polarized signal level measurements recorded in Durban for different rain attenuation bounds are compared with the theoretical results. Finally, the best theoretical model is used to estimate the seasonal cumulative distribution of rain attenuation for Durban, South Africa.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009RS004192

Determination of rain attenuation from electromagnetic scattering by spherical raindrops: Theory and experiment

The frequency range that extends from 70 to 115 GHz presents low gaseous attenuation and offers the possibility of implementing radio links with capabilities of transporting more than 1 Gb/s over distances up to a few kilometers. A better knowledge of the propagation characteristics of the atmosphere at these frequencies can benefit future technological advances, providing better performance in terms of the use of radio resources. Unfortunately, the number of propagation results communicated for this band is very small. In this paper, propagation in this frequency range is analyzed on the basis of two-year experimental measurements carried out in Madrid, Spain, on a commercial link working at 75 and 85 GHz. Rain attenuation is the most relevant propagation effect in the W-band. Attenuation measurements are processed to remove wet antenna effects, leaving only the path attenuation time series. Statistics obtained from these time series are compared with a number of model predictions that use rain information of various types as input data, assessing in this way their precision and usefulness.

Attenuation Measurements and Propagation Modeling in the W-Band

The rain attenuation from 1 to 1000 GHz was calculated by using both log-normal and Weibull distributions for raindrop size. The results were compared with the recent microwave measurements from 8.4 to 312.5 GHz at the rain rate R = 50 mm/h. The log-normal distribution leads to a higher estimate of attenuation than both the Weibull distribution and the experimental data.

Chii-Dong Chen

Papers

Rain attenuation from log-normal and Weibull raindrop-size distributions