WAVEGUIDE TRANSMISSION 301 



models to explain the phenomena which they observe in practice. It is be- 

 lieved that, for these people, this chapter together with a few key formulas 

 taken from the earlier sections will be helpful in gaining a fairly satisfactory 

 understanding of the practical aspects of waveguide transmission. 



At the lower frequencies, the current aspect of electricity meets most of 

 the needs and in comparison it is only occasionally that there is a need to 

 discuss lines of electric and magnetic force. In waveguide practice, on the 

 other hand, currents are usually not available for measurement and, al- 

 though we recognize their reality, they necessarily assume a secondary role. 

 In contrast with currents, we consider the fields present in a waveguide as 

 very real entities and we attach a very great importance to their orientations 

 as well as to their intensities. 



6.1 The Nature of Fields of Force 



As a suitable introduction to the discussion that follows, we shall review 

 some of the fundamental properties of lines of electric and magnetic force 

 and show pictorially the part that they play in transmission along an or- 

 dinary two-wire line. 



The Electrostatic Field- 

 As is well known, the concept of the electric field was devised by Faraday 

 to explain the force action between charged bodies. According to his view 

 there exist in the space between the charged bodies, lines or tubes of electric 

 force terminating respectively on positive and negative charges attached to 

 the bodies. These tubes of force are endowed with a tendency to become 

 as short as possible and at the same time to repel, laterally, neighboring lines 

 of force. Their direction at any point is purely arbitrary, but, by subsequent 

 convention, the positive direction is taken from the positively charged body 

 to the negative. This is such that a small positive charge (proton) placed in 

 the field tends to be displaced in the positive sense while an electron tends to 

 move in a negative direction. The force exerted on the unit charge is a 

 measure of the magnitude of the electric intensity E. It is measured in volts 

 per meter and, since it has direction as well as magnitude, it is a vector quan- 

 tity.^ Figure 6.1-1 illustrates in a general way the arrangement of lines of 

 electrostatic force that are assumed to exist between two oppositely charged 

 spheres. Also shown is a representative vector E. 



The Magnetostatic . Field 



In the same way that Faraday provided a satisfactory explanation for 

 the forces between charged bodies, so was he able to explain the forces be- 



1 Black-face type will be used when it seems desirable to emphasize the vector proper- 

 ties of quantities having direction as well as magnitude. 



