WAVEGUIDE TRANSMISSION 



313 



A particularly simple form of reflection occurs when the high-frequency 

 transmission line is terminated in a transverse sheet of metal of good con- 

 ductivity, as for example, copper. An arrangement of this kind is shown in 

 Fig. 6.2-5. As it is difficult to represent a wave front moving toward the 

 reflecting plate, we shall substitute an imaginary thin slice or section of the 

 electromagnetic configuration. A slice of this kind is shown in Fig. 6.2-5(a). 



Experiment shows that, at the boundary of the nearly perfect reflector, 

 the transverse electric force E is extremely small. This is consistent with 

 the sixth principle set forth in the previous section which states that there 

 can be no tangential component of electric force at the boundary of a per- 

 fect conductor. The result actually observed can be accounted for if it is 

 assumed that the reflecting conductor merely reverses the direction of lines 

 of electric force as they become incident, thereby giving rise to two sets of 



*^^^^^^^^^^^' S\\ 



ni 



^ 



^V \\^ \\\\\\\k\<\\<\\V' 



>r ,r 



i 



(a) (b) 



Fig. 6.2-5. (a) Propagation of an electromagnetic wave along a two-wire line terminated 



by a large conducting plate, (b) Representative lines of force reflected by the 



conducting plate. 



lines of force as shown in Fig. 6.2-5(b), one of intensity Ei = E directed 

 downward in the figure and moving laterally toward the metal sheet (in- 

 cident wave) and the other of intensity Er = —E directed upward and mov- 

 ing away from the metal sheet (reflected wave). Accordingly the resultant 

 electric intensity at the surface is zero. 



If the reflector is non-magnetic, the magnetic intensity H will be un- 

 affected by the reflecting material. We find by applying the right-hand rule 

 of Fig. 6.1-4 that the electric intensity E^ = — E when combined with H 

 constitutes a wave that must travel in a negative direction of v. This wave 

 may be represented by Equation 6.2-3. In a similar way the Poynting vector 

 which before reflection is represented by P = E x H now takes the form 

 P = (— ExH). The negative sign according to the right-hand rule of 

 Fig. 6.1-4 shows that the power approaching the conductor is reflected back 

 upon itself. If E and H are respectively equal in magnitude before and after 



