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.     

Moist-air attenuation at 96 GHz over a 21-km line-of-sight path

A propagation experiment at 96 GHz over a line-of-sight (LOS) path provided data on attenuation characteristics of atmospheric water vapor. Two consecutive time periods (three days in May and 1.5 days in August 1986) with a total of about 100 h of data on signal level and meteorological conditions were analyzed with respect to absolute humidity (3-21 g/m³) and temperature (4-32°C) variations. Experimental details, the data analysis, and a comparison with model predictions are discussed. The validity of the millimeter-wave propagation model is considered and it is concluded that the field experiment tends to uphold the validity of this model at 96 GHz     

Simplified analysis of line-of-sight propagation through rain at5-90 GHz

Attenuation and phase shift of narrowband signals at radar and higher frequencies due to atmospheric layers of hydrometers are usually analyzed by solving the scattering amplitude of one particle numerically and then applying the necessary many-particle statistics. A case is made for an important simplification: use of an analytical solution for the one-particle scattering amplitude that is basically an extension of the well-known low-frequency Rayleigh scattering amplitude with several empirical factors. This opens the road to predictions of 5-90-GHz signal deterioration from lower-frequency radar reflections yielding particle, statistics. Specifically, results for copolar and cross-polar discrimination of signal attenuation and for differential phase shifts are presented and compared, where possible, to known results     

Overwater line-of-sight fade and diversity measurements at 37 GHz

The results of line-of-sight propagation measurements at 37 GHz over a 10.0-mile overwater test site are presented. Measurements of the short-term fading statistics, and of the time, space, and frequency diversity parameters are included. Strong negative correlation was observed during both the space and frequency diversity measurements; negative correlation coefficients were as large as -0.8. The diversity improvement obtained was greater than the value expected from correlation calculations, which is attributed to the consistent occurrence of negative correlation in the vicinity of the interference nulls rather than the random occurrence assumed in the calculations. For the optimum case where maximum negative correlation occurs, sufficient diversity improvement is achieved with either space or frequency diversity to permit the elimination of almost the entire fade margin that is needed to overcome the multipath fading associated with reflections from the water surface.     

Comparison of simultaneous line-of-sight signals at 9.6 and 34.5 GHz

Signals at 9.6 and 34.52 GHz, propagated simultaneously over a slant line-of-sight overwater path, have been analyzed to compare the power spectra of phase-of-arrival variations and fading and to determine the coherence of these signals with regard to both phase variations and fading. The phase data at the two radio frequencies exhibited nearly identical power spectra from 0.01 to 5 Hz and very high coherence from 0.01 to 0.1 Hz. The coherence dropped rapidly above 0.1 Hz and was in most cases less than 0.4 above 0.5 Hz. The power spectra of fading were similar in shape at the two frequencies, but the fading spectral density was consistently higher at 34.52 GHz than at 9.6 GHz from 0.1 to 5 Hz. The shape of the coherence function for fading was similar to that of the corresponding phase coherence function, but the fading coherence was lower at the low spectral frequencies. The possible effect of the small spatial separation of the propagation path on the coherence analysis is discussed.     

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.     

Effect of wind on foliage obstructed line-of-sight channel at 2.5 GHz

A fixed terrestrial broadband wireless system such as MMDS (Multipoint Microwave Distribution System) is a cost effective solution for cable coverage to the immediate surrounding rural area. This wireless system can be operated with the existing cable headend and the same subscriber-end cable modem. Such a system works well with clear line-of-sight transmit/receive antennas. However, in near-line-of-sight transmission where a few foliated trees block the line-of-sight, signal distortion can occur, especially under conditions of high wind. The motion of the trees causes large and rapid signal fading. Measurements were taken on fixed wireless paths blocked with a few trees in the vicinity of the receive antenna. Fading characteristics of a 6 MHz channel centered at 2.545 GHz are provided. The fades are largely flat across the band but with some frequency selective fading. Fading rates under windy conditions ranged from 0.5 to 2 fades/second. The slope of the fades occasionally reached 50 dB/second.     

Wavelength dependence of scintillation fading at 110 and 36 GHz

Scintillation measurements made on 2 mm microwave links at 36 and 110 GHz along a common 4.1 km path across central London are described. Results are presented which show very good agreement with the theoretical predictions of Tatarski.     

Absorption and scintillation effects at 3 mm wavelength on a short line-of-sight radio link

Measurements on a path 150m long, with narrow-beam transmitting and receiving antennas 2m above the ground at one end of the path, and a reflecting plate at the other end, at the same height, have shown attenuation in rain to be about 17dB/km and 8dB/km for rainfall rates of 48mm/h and 7mm/h, respectively. Amplitude variations of up to ±0.4dB can occur in a time interval of the order of 1s during sunny, humid conditions in summer.     

Microwave emission and reflection from the wind-roughened seasurface at 6.7 and 18.6 GHz

Microwave radiometric observations were made with specially designed microwave radiometers at 6.7 and 18.6 GHz, and the results were compared with those of other investigators, over the frequency range of 1-40 GHz. Dependences of sea surface emission and reflection on wind speed, frequency, incidence angle, and polarization type are discussed in detail, following discussions of the reflective processes of sky radiation and error estimation in the retrieval of mainlobe-averaged brightness temperature. The wind speed sensitivity of brightness temperature, emissivity, and reflectivity is formulated with respect to frequency and incidence angle in each polarization. The brightness temperature, emissivity and reflectivity at arbitrary wind speed are derived employing this formulation. Based on the results obtained it is suggested that the 10-19-GHz band may be optimal for satellite microwave radiometer observations of sea-surface wind     

A comparative study of noise properties of Si IMPATT diodes operating at 80 GHz

The oscillator-noise properties of three kinds of Si IMPATT diodes operating at 80 GHz are measured. A DDR type of diode is superior in FM noise measure to the other two SDR types, one of which operates in the fundamental frequency mode and the other in the second harmonic frequency mode.     

Rain attenuation on satellite-earth paths at 11.4 and 14 GHz

Results are given of the analysis of several gears of radiometric measurements in the European region, carried out by the European Space Agency. Special attention is given to the attenuation statistics of the worst month in a calendar year and its relation to the yearly statistics. A total of 30 independent worstmonth fading distributions were used in the analysis. Furthermore, fade duration, diurnal variation and frequency dependence of fades are analysed.     

2.4GHz和5GHz WLAN干扰对比分析

通过对WLAN干扰机制和干扰类型进行较为详细的理论分析,然后进行了全面的实际测试,得出了2.4 GHz WLAN的干扰较严重,5 GHz WLAN干扰比较小的结论。这一结论为5 GHz WLAN的引入提供了较为有力的依据。     

Comparison of attenuation statistics at 19 and 37 GHz for Sun-Earth paths

For 0.2% of the observing time during May-August 1970, the attenuations at 19 and 37 GHz were about 3.8 and 10.2 dB, respectively, the larger value being the maximum measurable with the technique used in the investigation. Previous attenuation statistics published for 19 GHz are updated to cover the period June 1968-August 1970.     

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.     

Observed frequency scaling of amplitude scintillation at 20, 40, and 50 GHz

This paper presents an analysis of instantaneous frequency scaling of scintillation using propagation data recorded during a three month period (May-July 1997) at Sparsholt UK from the ITALSAT satellite beacons at frequencies 18.7, 39.6, and 49.5 GHz. Variations in the height of turbulence within reasonable limits were found to have a negligible effect on the scaling ratios. Furthermore, the exponent in the power law dependence of scintillation intensity on signal frequency was found to be on average 27% smaller than the theoretical value of 7/12 and to exhibit a slight diurnal effect. It is shown that this behavior can be partly accounted for by receiver thermal noise contribution to the measured signal variance. Ascribing the minimum observed short-term variance in each beacon to thermal noise and excluding this contribution yielded a higher exponent, which was nevertheless 15% below the theoretical value.     

Annual and annual-worst-month statistics of fading on Earth satellite paths at 11.5 GHz

Attenuation statistics from 19 site/years of 11.5 GHz radiometer measurements are presented for the European region. It is found that a factor between 6 and 7 is necessary to convert from annual-worst-month to yearly time percentages. A theoretical treatment is presented which shows excellent agreement with these results. Both the measurements and the analysis contradict a recent proposal for an upper bound of 4.41 on the conversion factor.     

Effect of tropospheric disturbances on a 4.1 and 6.2 GHz line-of-sight path

In order to have a better insight of the various fading mechanisms affecting a line-of-sight link, a thorough knowledge of the meteorological perturbation arising in the lower atmosphere is required. Continuous information about micrometeorological parameters of the lower atmosphere can be obtained by acoustic sounding (sodar). In effect, this technique allows continuous location and measurement of the intensity of thermal inhomogeneities of the atmosphere up to a height of about one kilometer and it can be used under clear, cloudy and foggy weather.     

Attenuation by cloud and rain on Earth-Sun paths at 12 to 71 GHz

A summary is given of all the attenuation data derived since June 1968 from sun-tracking radiometers located at the Appleton Laboratory, Slough. The new results at 37 and 71 GHz include data on the angular variation of attenuation and on the occurrence of fades exceeding specified values.     

磁扰和磁静期间南极McMurdo地区电离层闪烁统计特征的对比分析

利用南极McMurdo站（地理经纬度（166.73°E,77.88°S）,地磁纬度80°S）2011-2014年电离层闪烁观测数据,对比分析了磁扰和磁静期间电离层闪烁发生率的周日分布、季节分布,以及随太阳活动变化的统计特征.结果表明:磁扰和磁静期间电离层闪烁的周日分布均在磁中午附近和磁子夜后出现峰值,而磁扰期的闪烁发生率显著高于磁静期,并且闪烁发生范围向低纬和高纬方向扩展;春秋季电离层闪烁发生率明显高于夏冬季,每年的2、3月份和9、10月份高发,冬季6月份发生率最低;磁扰期的季节性特征比磁静期更为明显,且闪烁发生范围、发生频率均明显大于磁静期;太阳活动对电离层闪烁的影响十分显著,随着太阳活动的增强,闪烁发生的范围和发生频率均明显增大.该研究结果有助于了解极区电离层闪烁的整体分布情况,将为极区电离层闪烁建模以及闪烁预报提供支持,对极区通信、导航定位等有着重要的应用价值.