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1986 | Buch

Radiowave Propagation in Satellite Communications

verfasst von: Louis J. Ippolito Jr.

Verlag: Springer Netherlands

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Über dieses Buch

Radiowave Propagation in Communications was written with two basic objec­ tives: (l) to present an up-to-date review of the major radiowave propagation phenomena which hinder reliable space communications, and (2) to describe how these propagation phenomena affect the design and performance of satellite communications systems. Earth-orbiting satellites are employed extensively for the relay of information in a vast array of telecommunications, meteorological, government, and sci­ entific applications. Satellite systems rely on the transmission of radiowaves to and from the satellite and are dependent on the propagation characteristics of the transmission path, primarily the earth's atmosphere. Radiowave propagation thus plays a very important part in the design and ultimate performance of space communications systems. This book presents, for the first time, the meshing in a single publication of the fundamentals of radiowave propagation factors with a discussion of the practical consequences of these factors on satellite communications systems. Two major subfie1ds are involved in this book. Radiowave propagation, which is basically applied electromagnetic theory, provides the theory and an­ alytical tools for the first several chapters. Later chapters then apply propagation effects to the field of electrical engineering involved with satellite communi­ cations. The material progresses from the essential aspects of radiowave prop­ agation to the application of practical methods and techniques in the design and performance of satellite communications systems.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Introduction
Abstract
Earth-orbiting satellites are employed extensively for the relay of information in a vast array of telecommunications, meteorological, and scientific applications. These satellite systems rely on the transmission of radiowaves to and from the satellite and are dependent on the propagation characteristics of the transmission path, primarily the earth’s atmosphere. Radiowave propagation thus plays an important part in the design and ultimate performance of space communications systems.
Louis J. Ippolito Jr.
Chapter 2. Fundamentals of Radiowave Propagation
Abstract
In this chapter the fundamental elements of radiowave propagation are introduced. The basic transmission elements, such as free space attenuation, antenna gain, and polarization, are defined. Radiowave propagation modes and propagation mechanisms are discussed and the importance of the ionosphere and the troposphere in space communications is highlighted. Finally, the major radio-wave propagation factors in the frequency bands of interest to space communications are introduced and described.
Louis J. Ippolito Jr.
Chapter 3. Attenuation by Atmospheric Gases
Abstract
A radiowave propagating through the Earth’s atmosphere will experience a reduction in signal level due to the gaseous components present in the transmission path. Signal degradation can be minor or severe, depending on frequency, temperature, pressure, and water vapor concentration. In this chapter the effects of atmospheric gases, primarily oxygen and water vapor at space communications frequencies, are discussed, and methods for calculating the expected attenuation for a radiowave link are presented. Examples are given for atmospheric attenuation at several of the frequencies of interest for space communications systems. Atmospheric gases also affect radio communications by adding atmospheric noise (i.e., radio noise) to the link. This problem is described fully in Chapter 7.
Louis J. Ippolito Jr.
Chapter 4. Hydrometeor Attenuation on Satellite Paths
Abstract
The effects of precipitation on the transmission path are of major concern in space communications, particularly for those systems operating at frequencies above 10 GHz. Precipitation can have many forms in the atmosphere. Hydro-meteor is the general term referring to the products of condensed water vapor in the atmosphere, observed as rain, clouds, fog, hail, ice, or snow. The presence of hydrometeors in the radiowave path, particularly rain, can produce major impairments to space communications. Rain drops absorb and scatter radio-wave energy, resulting in signal attenuation (a reduction in the transmitted signal amplitude), which can degrade the reliability and performance of the communications link.
Louis J. Ippolito Jr.
Chapter 5. Rain Attenuation Prediction Methods
Abstract
The evaluation of the effects of rain on a satellite system design requires a detailed knowledge of the attenuation statistics for each ground terminal location at the specific frequency of interest. Direct long-term measurements of rain attenuation for all of the ground terminal locations in an operational network are not practical, therefore modeling and prediction methods must be used to make a best estimate of the expected attenuation for each location. Over the past several years extensive efforts have been undertaken to develop reliable techniques for the prediction of path rain attenuation for a given location and frequency, and the availability of satellite beacon measurements has provided a data base for the validation and refinement of the prediction models. This chapter reviews several of the more promising rain attenuation prediction techniques.
Louis J. Ippolito Jr.
Chapter 6. Depolarization on Satellite Paths
Abstract
The earth’s atmosphere can produce changes in the polarization sense of transmitted radiowaves. This effect is referred to as depolarization, or cross-polarization in the case of two independent waves which interfere with each other because of a depolarizing condition present in the transmission path.
Louis J. Ippolito Jr.
Chapter 7. Radio Noise in Satellite Communications
Abstract
There are several natural and man-made sources of unwanted external noise which can be introduced in the radiowave transmission of a space communications link. Any natural absorbing medium in the atmosphere which interacts with a radiowave will not only produce a signal amplitude reduction (attenuation), but will also be a source of thermal noise power radiation. The noise associated with these sources, referred to as radio noise, or sky noise, will directly add to the system noise through an increase in the antenna temperature of the receiver. For very low noise communications receivers, such as those in the NASA deep space tracking network, radio noise can be the limiting factor in the design and performance of the system.
Louis J. Ippolito Jr.
Chapter 8. Scintillation, Bandwidth Coherence, and other Propagation Factors
Abstract
In this chapter, several propagation factors introduced in Section 2.6 which have not yet been fully discussed in previous chapters are described. The factors described here are generally not as severe in earth-space communications as those described in earlier chapters, and they can be considered as secondary effects for most typical space communications links. There are special situations, however, where the effects can become significant, and these situations will be pointed out.
Louis J. Ippolito Jr.
Chapter 9. Propagation Effects on Communications Satellite Link Performance
Abstract
Prior chapters have focused on descriptions of the propagation factors that can degrade satellite communications links. Gaseous attenuation, hydrometeor attenuation, depolarization, radio noise, scintillation, and other factors were described, and methods for predicting the effects on communications links were presented.
Louis J. Ippolito Jr.
Chapter 10. Restoration Techniques for Overcoming Severe Attenuation
Abstract
A space communications system which is subject to weather dependent path attenuation can be designed to operate at an acceptable performance level by allowing adequate power margins on the uplink and the downlink segments. This can be accomplished directly by increasing antenna size, or increasing the RF transmit power, or both. Typically, power margins of 5–10 dB at C-band and 10–15 dB at K-band can be relatively easily achieved with reasonably sized antennas and with RF power within allowable levels. RF power levels are most likely constrained by prime power limitations on the satellite, and by radiated power limitations on the ground fixed by international agreement.
Louis J. Ippolito Jr.
Backmatter
Metadaten
Titel
Radiowave Propagation in Satellite Communications
verfasst von
Louis J. Ippolito Jr.
Copyright-Jahr
1986
Verlag
Springer Netherlands
Electronic ISBN
978-94-011-7027-7
Print ISBN
978-94-011-7029-1
DOI
https://doi.org/10.1007/978-94-011-7027-7