Chapter 1 



PROPAGATION OF RADIO WAVES: 

 INTRODUCTION AND OBJECTIVES 



» 1 FACTORS INFLUENCING PROPAGATION 



THE PROPAGATION of radio waves through the 

 atmosphere and around the curve of the earth, 

 at frequencies above 30 mc, is influenced by so many 

 factors that it is desirable to give first an overall 

 survey of the problem. This chapter presents the 

 problem of propagation in broad perspective in 

 contrast with many of the later chapters which are 

 devoted to detailed consideration of special phases 

 and methods of calculation. 



1.1.1 



Assignment 



The International Radio Wave Propagation Con- 

 ference recommended that a book be prepared deal- 

 ing with problems of radio wave propagation in the 

 standard atmosphere at frequencies above 30 mc. 

 The importance of these higher frequencies is appar- 

 ent when it is recalled that most radars operate in 

 this range and that an increasing number of com- 

 munication circuits are being equipped for operation 

 above this frequency. 



A certain amount of evidence from operational 

 theaters indicates that lack of familiarity with the 

 underlying theory of propagation and calculations 

 based thereon not infrequently has resulted in inef- 

 fective installation and operation of radar and com- 

 munication sets. This is ascribable, in part at least, 

 to the lack of publications which give a clear picture 

 of the problems of propagation or show how the 

 important factors may be evaluated. 



A considerable volume of basic material on propa- 

 gation had appeared in technical journals before 

 World War II, and during the war a great quantity 

 of classified material came from laboratories and 

 operational theaters illustrating new applications of 

 old principles, giving valuable information on propa- 

 gation problems as well as on characteristics of radar 

 and communication sets, antennas, targets, siting 

 problems, etc. But this information has not been 

 coordinated under one cover for practical use by sig- 

 nal personnel in the field. The Columbia University 

 Wave Propagation Group was asked to undertake 



this task, and it is hoped that this volume will, in 

 some measure, answer the need. 



' ' "^ Purpose 



Our effort then has been to provide a book, de- 

 signed for men with college training in radio, physics, 

 or electrical engineering, which: 



1. States the basic laws of propagation, that is, 

 shows how the characteristics of the earth and the 

 atmosphere control the propagation of radio waves; 



2. Gives the fundamental properties of the basic 

 types of antenna systems, particularly their direc- 

 tivity and gain; 



3. Gives the reflecting properties of targets such 

 as airplanes for use in detection by radar; 



4. Teaches the reader how to calculate field 

 strength or obtain the coverage diagrams, given a 

 particular set, power, and site ; 



5. Gives the fundamental information required in 

 the above calculations for application to the radar 

 and communication sets used in operational theaters ; 



6. Provides illustrative material and sample cal- 

 culations which show how the laws of propagation 

 may advantageously be used in the location and 

 operation of radar systems, communication sets, and 

 countermeasure equipment designed to deceive the 

 enemy and to prevent jamming of equipment b}^ 

 enemy action or by mutual interaction of our own 

 sets. 



12 FUNDAMENTAL PROBLEMS 



AND LIMITATIONS 



1.2.1 Meaning of Propagation 



By propagation is meant the movement of radio 

 waves through the atmosphere, and the transfer, by a 

 wave mechanism, of radiant energ}^ from a transmit- 

 ting antenna to a receiving antenna. The problem 

 of propagation requires an understanding of the 

 manner in which the wave energy is emitted and 

 received as well as of the manner in which it flows 

 through the atmosphere. The radio engineer must 



