Attenuation Measurements in the 1 to 1000 MHz Frequency Range in Wet Granite Tunnels

Attenuation measurements were made in the 1 to 1000 MHz frequency range in two wet-granite tunnels leading to an underground facility. The purpose of the measurements was to determine the vulnerability of the facility to interfering electromagnetic radiation. Continuous-wave signals were propagated within the tunnels and the signal levels at various distances from the transmitter were measured with a spectrum analyzer. Measurements were made using antennas to launch and receive the signals and also using baluns to conduct the signals directly to longitudinal metallic structures. These structures consisted of ventilation ducts and of the sheaths on power cables and coaxial cables. At low frequencies, the path attenuation was on the order of 2 dB/100 ft. (0.07 dB/m). The results show that this low attenuation probably resulted from the presence of the longitudinal metallic structures in the tunnels. The maximum path attenuation occurred at 50 MHz in one tunnel and at 200 MHz in the other (smaller tunnel). Then, at higher frequencies, it is thought that propagation occured in a waveguide-like manner. At the higher frequencies, it was found that bends in the tunnels significantly increased the attenuation. It is concluded that if interfering signals in the MHz range are anticipated, tunnels free of longitudial metallic structures should be used. To prevent interference by higher frequencies, where waveguide-like propagation occurs, tunnels should contain bends.     

Time delay spread measurements at 850 MHz and 1.7 GHz inside a metropolitan office building

Time delay spread and signal level measurements were made in a multistoried office building in New York City at 850 MHz and 1.7 GHz. No significant statistical difference in time delay spread was found at the two frequencies. The maximum root-mean-square time delay spread at both frequencies did not exceed 100 ns. Attenuation was very nearly the same at the two frequencies, within the limits of the experiment's accuracy.<>     

UHF、L频段陆地卫星移动通信业务遮蔽环境衰落研究

ＵＨＦ、Ｌ频段路边树遮蔽和多径衰落实验分别于１９９９年８月和９月在河南安阳境内进行。利用日本ＧＭＳ１４０Ｅ气象卫星为信标,其下行频率分别为４６８．９２４ＭＨｚ和１６９１．００ＭＨｚ,有效全向辐射功率分别为３７ｄＢｍ和５６ｄＢｍ,中频带宽分别为２ｋＨｚ和２００ｋＨｚ,极化方式均为线极化。地面接收系统和数据处理设备安置于汽车上。此项实验的目的是为地面卫星移动通信系统的设计提供重要的信道参数。本文给出了     

Radio wave propagation through woods

In 1997 and 1998, measurements were made of radio wave attenuation through a cottonwood plantation at the University of Illinois at Urbana-Champaign, on a number of frequencies between 27 and 411 MHz. Based on these measurements, an empirical formula that describes radio wave attenuation was developed     

Some Propagation Experiments Relating Foliage Loss and Diffraction Loss at X-Band and UHF Frequencies

Measurements of signal attenuation were made from a suburban hilltop base station to a mobile vehicle on several streets in the surrounding countryside. Measurements of signal strength were simultaneously made in the winter of 1971 at frequencies of 836 MHz and 11.2 GHz and then repeated in the summer to determine the effects of foliage. The presence of foliage reduced the received signal strength and the effect was more pronounced atX-band than at UHF. In cases where the shadowing obstacle was tree covered, signal levels at UHF might typically be 10 dB lower when the trees were in full leaf, whereas atX-band this additional loss could be as high as 20 dB. The experimental data was compared to values predicted by knife-edge diffraction and reasonable agreement was found.     

Some propagation experiments relating foliage loss and diffraction loss at X-band and UHF frequencies

Measurements of signal attenuation were made from a suburban hilltop base station to a mobile vehicle on several streets in the surrounding countryside. Measurements of signal strength were simultaneously made in the winter of 1971 at frequencies of 836 MHz and 11.2 GHz and then repeated in the summer to determine the effects of foliage. The presence of foliage reduced the received signal strength and the effect was more pronounced at X-band than at UHF. In cases where the shadowing obstacle was tree covered, signal levels at UHF might typically be 10 dB lower when the trees were in full leaf, whereas at X-band this additional loss could be as high as 20 dB. The experimental data was compared to values predicted by knife-edge diffraction and reasonable agreement was found.     

Precipitation attenuation studies based on measurements of ATS-6 20/30-GHz beacon signals at Clarksburg, MD

COMSAT Laboratories participated in the millimeter wavelength propagation experiment under NASA contract NAS5- 20740, performing measurements of the 20/30-GHz ATS-6 satellite beacon signals and auxiliary measurements such as radiometric sky temperature and minute precipitation at Clarksburg, MD. These measurements were intended to broaden the data base required to advance the understanding of the propagation characteristics of the earth-satellite path at frequencies over 10 GHz. A correlation is established between direct measurement of attenuation of the signal radiated from the satellite and the indirect measurement of attenuation by auxiliary ground-based equipment. The indirectly derived statistics agreed reasonably well or can be reconciled with earlier published results and may therefore be used as a basis for estimating long-term cumulative attenuation statistics.     

Equatorial scintillations: A review

With the advent of satellite communications systems at frequencies varying fromsim140MHz to 1600 MHz as well as navigation and ranging systems in the 1200-1600 MHz portions of the spectrum, the effect of equatorial irregularities on fading signals has become of importance. Recent observations of the signal statistics of scintillations at frequencies ranging from 136 MHz to 6 GHz reveals a power law fall off of irregularity sizes. Power spectra are now available for a variety of conditions and for frequencies from VHF to microwaves. During periods of intense equatorial activity, at frequencies to 360 MHz, Rayleigh scattering is frequently experienced. The latitudinal extent of the scintillation irregularity region has been established with a half occurrence width during years of moderate solar flux of plus and minus12deg. A correlation of in-situ measurements of irregularities from satellites had revealed the great variations in longitudinal patterns during any season. It has also allowed theDelta Nobtained from in-situ measurements to be utilized to predict scintillation excursions. New facets of scintillation activity in the equatorial region recently reported include weak daytime scintillation and the patchy nature of irregularities (small irregularities embedded in large structures) particularly noted during periods of low solar flux. Future studies will assist in the delineation of the extent of the equatorial region at frequencies from 1.5 to 6 GHz, and in the UHF range. From the viewpoint of the communicator the morphology of scintillations at microwaves has still not been reported from any long term program of measurements.     

An adaptive propagation prediction program for land mobile radiosystems

This paper describes the development of an adaptive RF propagation prediction program for land mobile radio systems. The program, which allows the user to specify transmitted signal strength, carrier frequency, base station antenna height, and mobile vehicle antenna height also provides the information necessary to determine a level of confidence for its predictions. In lieu of detailed topographical data (which is unavailable for many regions), the program makes use of data files containing the results of received signal strength measurements previously taken within the geographic region of interest at various locations, various carrier frequencies (measurements were taken at 453, 922, 1310, 1430, and 1920 MHz), and various base station antenna heights. This paper concludes by providing examples of results illustrating the performance of the adaptive propagation prediction program, showing that the proposed program yields significant improvement in propagation prediction and level of confidence when compared to currently available tools     

Improved numerical solution of Ott's integral equation for HFground wave attenuation

An alternative solution is presented for Ott's (1970) integral equation for the attenuation of a high-frequency vertically polarized radio signal propagating over rough inhomogeneous terrain. The method circumvents the numerical stability occurring with an earlier method at steep slopes and/or high radar frequencies. The method is illustrated by application to a steep profile at 20.08 MHz. The obtained values for the attenuation function agree well with experimental measurements     

建筑物对通信信号衰减的定量研究

建筑物墙体对信号的衰减对于通信信号在城市环境中的传播影响很大,透射信号的衰减是影响通信质量的重要方面。文中采用自由空间法建立测试系统,在300M～3GHz的频率范围之间对不同建筑物墙体进行信号穿过墙体透射衰减的实地测量,通过加权的算法得到建筑物的等效介电常数。同时,通过在固定频率下透射波和空旷地接受信号场强的比较计算得到透射系数,利用上述的固定频率下透射系数和等效介电常数结合菲涅尔公式反演其该频率下的等效电导率,得出建筑物墙体等障碍物在不同频率下的等效电导率。利用基于时域有限差分差分法的XFDTD软件进行仿真计算,结果验证仿真结果和实际测量结果比较吻合。     

815 MHz radio attenuation measured within two commercial buildings

Copolarized attenuation measurements were made at 815 MHz inside two office/laboratory buildings. For the propagation paths along a straight corridor and into a adjoining room received signal power decayed with distance as d^-3.6. Signal powers higher than their free-space values were routinely measured for line-of-sight paths along a corridor. As expected, isolation between floors and between parallel corridors is heavily dependent on building construction techniques. Energy propagates selectively in directions not blocked by large amounts of metal. Cross-floor isolations of 26 dB were measured between floors separated by solid sheet metal. Coupling between otherwise isolated corridors was produced by an open central cavity in the larger building     

On the Use of Radiometric Measurements to Estimate Atmospheric Attenuation at 100 and 300 GHz

At frequencies of between 100 GHz and 30 THz, propagation conditions are severely affected by the influence of the composition and phenomena of the troposphere. This paper focuses on the use of radiometric measurements to estimate attenuation at 100 and 300 GHz, considering non-scattering scenarios, in which the main contributions are given by atmospheric gases and non-rainy clouds. These techniques allow the estimation of the absorption loss through the entire atmosphere, without the need for a signal source situated in a satellite or a high altitude aircraft. On the basis of well-accepted absorption models, the results of calculating gaseous, cloud, and total attenuation using 3-year meteorological data from Madrid, Spain, are detailed, as well as estimates of the expected values of the sky brightness temperature as measured by the radiometer. Finally, based on the results obtained, a discussion on the use of radiometric measurements at both frequencies is presented, in connection with an experimental campaign currently under preparation.     

Seasonal and diurnal variations of total attenuation measured with the ITALSAT satellite at Spino d'Adda at 18.7, 39.6 and 49.5 GHz

The ITALSAT satellite experiment started in January 1991 and ended in January 2001, permitting an extensive program of propagation measurements at 18.7, 39.6 and 49.5 GHz. In these frequency bands, up‐ and down‐links experience severe signal attenuation due to meteorological effects such as those due to gas (oxygen and water vapour), clouds, turbulence and, especially, rain. The propagation measurement campaigns aim mainly at assessing and at modelling the appropriate fade margin compensating propagation attenuation in the design of satellite communication systems. This margin depends significantly on the season and on the time of the day, due to variations of meteorological conditions. This paper reports the results obtained from copolar signal measurements carried out at the Earth station of Spino d'Adda, near Milano (North Italy), at the three frequencies during 7 years (from 1994 to 2000). The measured cumulative distribution functions of total attenuation are compared to ITU‐R models' prediction. Moreover the statistics conditioned to single months of the year, seasons and 4 h contiguous periods of the day are also shown. These statistics can be useful for telecommunication systems whose service quality and design must be matched to the season of the year or the time of the day. Copyright © 2004 John Wiley & Sons, Ltd.     

Ka-band propagation measurements: an opportunity with the AdvancedCommunications Technology Satellite (ACTS)

The Advanced Communications Technology Satellite (ACTS) was conceived at the National Aeronautics and Space Administration (NASA) as a follow on program to its long history in satellite communications projects that have reduced the risk of developing new technologies that fall outside the sponsorship capability of the private sector. To counter the foreign challenge that developed in the late 1970's to the once insuperable US lead in this field, ACTS was developed to maintain the US preeminence. Launched in September 1993 from the space shuttle, key technologies on ACTS include a multibeam antenna, a baseband processor, a 900 MHz wideband microwave switch matrix, adaptive rain fade compensation techniques, and the use of Ka-band frequencies. Since this is the United States' first effort in using Ka-band for satellite communications, beacons are incorporated on the satellite, which provide an opportunity for propagation measurements. NASA is sponsoring a network of propagation experimenters using these beacons and receive-only terminals identical in design. This paper provides some history that leads to the eventual development of ACTS. Also, a system overview of the spacecraft is provided for those less familiar with it     

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.     

Rain-induced attenuation for Ku-band satellite communications in the west coast of Peninsular Malaysia, Penang

Accurate rainfall rate is important for predicting rain attenuation over a satellite link. Raindrops are able to take in, spread out, and change the polarization of satellite signals that pass through the atmosphere of the earth, especially in equatorial regions like Malaysia where heavy rainfall normally occurs. Satellite communications system network operating at Ku-Band will experience rain fade due to absorption and scattering of signal. This paper aims to discuss the range of effects of rain on the transmission of electromagnetic signal and to determine the significance of rainfall rate in the prediction of rain attenuation based on measurements carried out in the northern region of Peninsular Malaysia (Penang). At 0.01% of time, 140?mm/h and 22?dB of rain rate and attenuation were observed, respectively.     

ACTS propagation experiment: experiment design, calibration, anddata preparation and archival

The National Aeronautics and Space Administration Advanced Communications Technology Satellite (ACTS) propagation experiment was designed to obtain slant-path attenuation statistics for locations within the United States and Canada for use in the design of low-margin Ka-band satellite communication systems. Experimenters at seven different locations have collected propagation data for move than two years. The propagation terminals used for the experiment were identical. A single preprocessing program was used by the experimenters to provide for automatic calibration, generation of attenuation histograms, and data archival. In this paper, the calibration procedures are described mid estimates given for measurement accuracy. ACTS provided beacons at 20.2 and 27.5 GHz for use in making attenuation measurements. In addition to the beacon receivers, each ACTS propagation terminal has two total power radiometers with center frequencies at the beacon frequencies. The radiometers are used to establish the beacon signal reference levels needed for calculating beacon attenuation values. For the combined radiometer and beacon measurement system, the attenuation measurement error was less than a maximum of 1.0 dB and was generally less than 0.3 dB. The dynamic range for attenuation measurement varied from site to site depending on location relative to the peak of the satellite beacon antenna pattern. For locations within the continental United States, the dynamic range was better than 20 dB     

Attenuation statistics in Italy as measured by the SIRIO satellite during its five year lifetime

The results of a campaign of attenuation measurements carried out by means of the Italian satellite SIRIO at the two frequencies 11.6 and 17.8 GHz are presented. The campaign lasted five years (1978- 1982) and yielded almost continuous measurements at the lower frequency (acquired in three Italian stations) and measurements for a considerable fraction of time at the higher one (acquired in two of the three stations). The major aim of these measurements was to acquire long-term statistics to be employed in future earth-space radiolink design. This objective has been fully accomplished, owing to the very long life of the satellite, and the acquired data have been already utilized, properly extrapolated in frequency, for designing the domestic satellite system Italsat planned to start in 1987. Year-to-year and site-to-site variation have been found to be very high. Conversely the ratio between equiprobable values of attenuation at the two frequencies has proved to be very similar in the two stations and rather stable across the attenuation range.     

Propagation model for building blockage in satellite mobilecommunication systems

A propagation model for building blockage in satellite mobile communication systems is developed. This model characterizes the signal transmitted from a low-Earth orbiting (LEO) satellite when there is an obstruction in the path of the signal. The obstruction is assumed to be a man-made structure. The analysis is performed using the uniform theory of diffraction (UTD). Using this method, both single and double diffractions from the structure edges were included. Direct and reflected rays from the ground and building were also included, whenever the satellite signal was not completely obstructed. The satellite is assumed to be moving along a circular orbit while the receiver is stationary. The normalized signal level (in decibels) and the signal attenuation rate (in decibels per second) are computed. Such information is considered very useful in developing the mobile system's hand-off algorithm