WAVEGUIDE TRAiVSAflSSION 



309 



interference. Certain specific examples will be discussed later, but first we 

 shall discuss a somewhat simpler case. 



The Infinite Line 



Let us take, for discussion, a uniform two-wire line that is infinitely long. 

 Waves launched on such a line are assumed to be propagated to infinity. 

 There are no reflected components and hence no wave interference. If the 

 frequency is very high, the forerunners of the lines of force sent out by the 

 source will not have traveled very far when the emf at the source will have 

 reversed its direction. This gives rise at the source to a second group of lines 



CIRCLE ENCLOSING ONE HALF 

 TRANSMITTED POWER 



(a) 



■1 



c o 



kA 



3 D ir V 



■LINES OF ELECTRIC FORCE LINES OF MAGNETIC FORCE 



• OUT OIN 



(b) 









Fig. 6.2-3. (a) Arrangement of lines of electric and magnetic force in both the longitudinal 

 and transverse sections of an infinitely long transmission line, (b) Space relationship 

 between electric vector E and magnetic vector // as observed in a plane containing 

 the two conductors. 



of force exactly like the first except oppositely directed. This, in turn, will be 

 followed by a third group identical with the first and a fourth identical with 

 the second and so forth until equilibrium is reached. Because the lines of 

 electric force are in motion, we must expect them to be accompanied by 

 lines of magnetic force. Both are of equal importance. Therefore it is not 

 correct to refer to either alone as a distinguishing feature of the wave. Both 

 components are shown in cross section at the right in Fig. 6.2-3 (a). 



The distance between successive points of the same electrical phase in a 

 wave is known as the wavelength X. It depends on the frequency/ of alterna- 

 tion and the velocity of propagation v\\ — v/f. The velocity of propagation 

 in turn depends on the nature of the medium between the two wires. For 



