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NASA NTRS1973

ATS-5 millimeter wave propagation measurements

Long term experimental measurements to determine the propagation characteristics of 15 and 32 GHz earth-space links and to evaluate performance characteristics of operational millimeter wave systems are reported. The ATS 5 millimeter wave experimental link experienced attenuation and fading characteristics as a function of rainfall rate and other meteorological parameters. A method of site selection for the lowest attenuation rainfall rate improved reception tremendously.

Ippolito, L. J.↗

NASA NTRS1973

A simple method for the determination of effective rain cell dimensions and orientation

A simple method is proposed for the determination of effective rain cell dimensions and orientation. Two rain cell models were considered: the circular cell and the elliptical cell. In both models it is assumed that the rain rate is constant throughout the cell, that all cell locations are equally likely, and that the cell dimensions depend upon the rain rate. It is then shown that the effective cell dimensions and orientation may be deduced from rain rate statistics accumulated at two or three closely spaced sites, depending upon the model chosen. The results of this study alone with previous estimates of rain cell dimension indicate that the rain rate measurement points should be spaced on the order of one-half kilometer apart. The proposed method is simple and relatively inexpensive; thus, this approach is readily suited to the study of the dependence of rain cell size and orientation upon climatic region. The resulting rain cell characteristics are of direct value in the prediction of millimeter wavelength attenuation statistics on both single-terminal and diversity earth-space propagation paths as well as point-to-point terrestrial links.

Hodge, D. B.↗

NASA NTRS1974

Path diversity for reception of satellite signals

The improved system performance resulting from the use of path diversity on earth-space satellite links operating above 10 GHz is discussed. Diversity gain is defined, and it is noted that the optimum diversity gain may be determined quite simply from the knowledge of a simple terminal fade distribution only. This approach may be extended to an arbitrary number of diversity terminals. The available diversity gain data are compared and shown to be consistent. These data, resulting from measurements in Ohio and New Jersey, indicate that diversity gain becomes relatively independent of separation distance for separations greater than approximately 8 km.

Hodge, D. B.↗

NASA NTRS1975

ATS-6 millimeter wavelength propagation experiment

An empirical relation for path diversity gain as a function of terminal separation distance and single site fade depth is presented. This relation is based on existing 15.3 GHz ATS-5 attenuation data and 16.0 GHz radiometric temperature data for earth-space propagation paths. Preliminary 30 GHz ATS-6 diversity data are presented and are found to agree well with this empirical relation.

Hodge, D. B.↗

NASA NTRS1975

Twenty and thirty GHz millimeter wave experiments with the ATS-6 satellite

The ATS-6 millimeter wave experiment, provided the first direct measurements of 20 and 30 GHz earth-space links from an orbiting satellite. Studies at eleven locations in the continental United States were directed at an evaluation of rain attenuation effects, scintillations, depolarization, site diversity, coherence bandwidth, and analog and digital communications techniques. In addition to direct measurements on the 20 and 30 GHz links, methods of attenuation prediction with radars, rain gages, and radiometers were developed and compared with the directly measured attenuation. Initial data results of the ATS-6 millimeter wave experiment from the major participating organizations are presented.

Ippolito, L. J.↗

NASA NTRS1975

ATS-6 - Millimeter Wave Propagation and Communications Experiments at 20 and 30 GHz

The Applications Technology Satellite (ATS-6) Millimeter Wave Experiment, developed and implemented by the NASA Goddard Space Flight Center, has provided the first direct measurements of 20- and 30-GHz earth-space links from an orbiting satellite. Studies at eleven locations in the continental United States were directed at an evaluation of rain attenuation effects, scintillations, depolarization, site diversity, coherence bandwidth, and analog and digital communications techniques. In addition to direct measurements on the 20- and 30-GHz links, methods of attenuation prediction with radars, rain gauges, and radiometers were developed and compared with the directly measured attenuation. This paper presents a review of the major results of the first year of measurements with ATS-6, with emphasis on the impact of the measurements on millimeter wave space systems design.

Ippolito, L. J.↗

NASA NTRS1975

The GSFC 20 and 30 GHz millimeter wave propagation experiment

The Goddard Space Flight Center Millimeter Wave Experiment (MWE) aboard ATS-6, designed to evaluate the propagation characteristics of earth-space communications links at 20 and 30 GHz, is outlined, and the major results to date are presented. The 20 and 30 GHz transmitters operate through spot beam or continental coverage antenna systems. The transmitted signals consist of 9 tones spaced out to 1440 MHz. A communications link 6 GHz up and 20 or 30 GHz down is provided. Attenuation ratio measurements between the 20 and 30 GHz links indicate values higher than those predicted. Clear sky scintillations have been observed with spectral components up to about 50 Hz. Observations of rain depolarization indicate that attenuation effects predominate over depolarization effects in frequency re-use communications systems in the 20 GHz region. Various methods of predicting path attenuation are under investigation.

Ippolito, L. J.↗

NASA NTRS1976

An empirical relationship for path diversity gain

Existing 15.3 and 16 GHz path diversity gain data for earth-space propagation paths are used to generate an empirical relationship for diversity gain as a function of terminal separation distance and single terminal fade depth. The agreement between the resulting closed form expression and the data is within 0.75 dB in all cases.

Hodge, D. B.↗

NASA NTRS1975

The GSFC 20 and 30 GHz millimeter wave propagation experiment

The preliminary results of the Goddard Space Flight Center Millimeter Wave Experiment, flown aboard ATS-6 to investigate the propagation characteristics of earth-space communications links at 20 and 30 GHz, are discussed. The spacecraft transmitters operate through spot beam (2 deg) or continental coverage (6 by 9 deg) antenna systems. The transmitted signals consist of a set of nine tones spaced out to 1440 MHz to allow measurement of wideband attenuation and coherence through precipitation. Initial data on precipitation depolarization and attenuation effects indicate that attenuation effects will exert the stronger influence on the design of frequency re-use communications systems in the 20 GHz region. The use of four ground terminals separated by 30 to 78 km to reduce the effects of rain attenuation has been successful, with improvement approaching the theoretical maximum demonstrated for five events. Preliminary results on the use of on-beam radar measurements for predicting rain attenuation are encouraging.

Ippolito, L. J.↗

NASA NTRS1976

The OSU self-phased array for propagation measurements using the 11.7 GHz CTS beacon

A self phased array was developed for propagation measurements on an earth-space path. The 11.7 GHz CTS beacon was used as the signal source. The self phased array was used to measure angle of arrival as well as attenuation and scintillation statistics. The performance of the array is described, and sample data are presented. The tracking capability of the self phased array was also studied. This technique permits fully electronic, nonmechanical satellite tracking, thus simplifying unmanned operation and eliminating severe weather tracking constraints.

Theobold, D. M.↗

NASA NTRS1977

Amplitude scintillation at 2 and 30 GHz on earth space paths

Extensive amplitude scintillation measurements were made simultaneously at 2.075 and 30 GHz on earth-space propagation paths. These measurements were performed as the Applications Technology Satellite (ATS-6) was moved slowly from a synchronous position over India to a new synchronous position over the United States. The variance, path loss, covariance, and spectra are discussed as functions of the path elevation angle. These results are also compared with earlier simultaneous scintillation measurements at 20 and 30 GHz during the movement of ATS-6 to its position over India.

Hodge, D. B.↗

NASA NTRS1977

Amplitude scintillation at 2 and 30 GHz on earth space paths

Extensive amplitude scintillation measurements have been made simultaneously at 2.075 and 30 GHz on earth-space propagation paths. These measurements were performed as the Applications Technology Satellite (ATS-6) was moved slowly from a synchronous position over India to a new synchronous position over the United States. The variance, path loss, covariance, and spectra are discussed as functions of the path elevation angle. These results are also compared with earlier simultaneous scintillation measurements at 20 and 30 GHz during the movement of ATS-6 to its position over India.

Hodge, D. B.↗

NASA NTRS1978

A global model for rain attenuation prediction

A model was developed for the prediction of rain attenuation statistics for 8 rain rate climate regions spanning all land regions from the equator to the poles. The model uses empirically determined rain rate distributions for each climate region and an empirical model to estimate path averaged rain rate for given values of point rain rate. Attenuation distribution observations were compared with model predictions. Good agreement was obtained for earth-space paths at 0.1 percent of the year. At the extremes, 0.01 and 1 percent of the year the observations were generally within the model estimate bounds but the agreement is not as good as at 0.1 percent of the year. The discrepancies are attributed to the limited duration of the attenuation observations and to the limited number of rain rate distribution observations.

Crane, R. K.↗

NASA NTRS1979

Transionospheric propagation predictions

The current status and future prospects of the capability to make transionospheric propagation predictions are addressed, highlighting the effects of the ionized media, which dominate for frequencies below 1 to 3 GHz, depending upon the state of the ionosphere and the elevation angle through the Earth-space path. The primary concerns are the predictions of time delay of signal modulation (group path delay) and of radio wave scintillation. Progress in these areas is strongly tied to knowledge of variable structures in the ionosphere ranging from the large scale (thousands of kilometers in horizontal extent) to the fine scale (kilometer size). Ionospheric variability and the relative importance of various mechanisms responsible for the time histories observed in total electron content (TEC), proportional to signal group delay, and in irregularity formation are discussed in terms of capability to make both short and long term predictions. The data base upon which predictions are made is examined for its adequacy, and the prospects for prediction improvements by more theoretical studies as well as by increasing the available statistical data base are examined.

Klobucher, J. A.↗

NASA NTRS1980

Millimeter wave attenuation prediction using a piecewise uniform rain rate model

A piecewise uniform rain rate distribution model is introduced as a quasi-physical model of real rain along earth-space millimeter wave propagation paths. It permits calculation of the total attenuation from specific attenuation in a simple fashion. The model predications are verified by comparison with direct attenuation measurements for several frequencies, elevation angles, and locations. Also, coupled with the Rice-Holmberg rain rate model, attenuation statistics are predicated from rainfall accumulation data.

Persinger, R. R.↗

NASA NTRS1981

The CTS 11.7 GHz angle of arrival experiment

The objective of the experiment was to determine the statistical behavior of attenuation and angle of arrival on an Earth-space propagation path using the CTS 11.7 GHz beacon. Measurements performed from 1976 to 1978 form the data base for analysis. The statistics of the signal attenuation and phase variations due to atmospheric disturbances are presented. Rainfall rate distributions are also included to provide a link between the above effects on wave propagation and meteorological conditions.

Kwan, B. W.↗

NASA NTRS1981

Radio propagation for space communications systems

This paper presents a review of the most recent information on the effects of the earth's atmosphere on space communications systems. Models and techniques used in the prediction of atmospheric effects as influenced by frequency, geography, elevation angle, and type of transmission are discussed. Recent data on performance characteristics obtained from direct measurements on satellite links operating to above 30 GHz are reviewed. Particular emphasis is placed on the effects of precipitation on the earth-space path, including rain attenuation, and rain and ice-particle depolarization. Sky noise, antenna gain degradation, scintillations, and bandwidth coherence are also discussed. The impact of the various propagation factors on communications system design criteria is presented. These criteria include link reliability, power margins, noise contributions, modulation and polarization factors, channel crosstalk, error-rate, and bandwidth limitations.

Ippolito, L. J.↗

NASA NTRS1981

Propagation data bases

Existing data bases accumulated as the result of experiments to gather propagation data on millimeter wave Earth-space links are described. The satellites used are described and results of the significant experiments conducted in the United States are summarized. The data bases consist primarily of cumulative attenuation statistics, though some depolarization measurements are included. Additional summaries of propagation data are cited.

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