Polarization in electromagnetic systems, 2nd. ed.

Abstract

Polarization is the fourth dimension of electromagnetic waves, with the other three being frequency, direction of propagation, and intensity. Of the four dimensions in electromagnetic systems, polarization is often the most misunderstood and neglected. If polarization is not properly included in the design phase of systems, performance can be seriously compromised or the system can even fail. On the other hand, polarization features can be exploited in communication systems to improve reliability and increase capacity. In sensing applications, multiple polarizations are used to increase information about targets and scenes. This book had its beginnings with a technical report published by the author in 1977 and submitted to the research sponsor, NASA. The associated research was on Earth-space propagation in the 10 to 30 GHz frequency range. At these frequencies rain along the propagation path can cause severe attenuation and depolarization and thus the frequencies were not used at the time. Virginia Tech was among the first few organizations in the world to investigate the effects with the goal of understanding propagation impairments and of learning how to configure systems to use dual polarization to double satellite communications capacity. The depolarization effects of rain on communication links were investigated through extensive measurement programs, including a terrestrial link and satellite links using the ATS-6, CTS, COMSTAR, SIRIO, INTELSAT, and OLYMPUS satellites. The mathematical representations of polarization and the models to predict weather induced impairments were developed and verified with measured data. The models were used by government and industry to design systems that implement dual polarization on satellite links, which are now common in today’s operational systems. Colleagues and engineers in industry who used the report encouraged me to turn the report into this book. This second edition is an expanded and reorganized version of the first edition, which was published in 1993. It now has two parts. Part I covers the fundamental theory and mathematical formulations. Part II applies the fundamentals to application areas such as antenna polarization, antenna-wave interaction, dual-polarized systems, and depolarizing media. New to the second edition is specific information on applications to: wireless communications, adaptive systems, radar, and radiometry. Chapter 9 on wireless communication systems is entirely new. Chapter 10 is a greatly expanded treatment of measurement considerations for polarization. The book should be useful to the practicing engineers involved with antennas, propagation, communications, radar, or radiometry. It is organized for rapid understanding of the principles and for easily locating material needed in computations. At the same time, the book is suitable for use in the classroom, especially as a part of radio systems-oriented courseware that is intended to study the complete propagation channel. Several examples with full computations are included to reinforce the important quantative concepts. Many end-of-chapter problems have been included for self-study enrichment and for classroom use. It is assumed that the reader has some knowledge of electromagnetics, but he/she need not have a complete understanding of electromagnetic theory. Maxwell’s equations will not be presented or solved. Instead, Chapter 2 presents the needed formulas for wave polarization calculations. Emphasis is always on understanding the concepts and mathematics needed for system calculations. Chapter 3 presents the polarization state representations. The techniques for treating partially polarized waves are presented in Chapter 4. Chapter 5 starts Part II. It treats antenna polarization (greatly expanded from the first edition) with many examples of specific antennas that can be used for generating linear, circular, and dual polarization. The important problem of computing the power received by an arbitrarily polarized wave incident on a receiving antenna is presented in Chapter 6. Dual-polarized radio systems are presented Chapter 7, including system evaluation methods and hardware components needed to implement dual polarization. Chapter 8 covers all aspects of medium effects on polarized waves, including propagation through a medium and reflections from media. Applications to communications, radar, and radiometry are included. Chapter 9 treats many topics in wireless communications related to polarization, such as frequency reuse with dual polarization and polarization diversity. Chapter 10 presents principles and techniques for measuring the polarization of waves and antennas.