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form plane waves multiply reflected between opposite walls of the guide. 

 This viewpoint accounts for not only the distribution of the lines of force 

 in the wave front but also for the velocity at which the phase progresses 

 and the velocity at which energy is propagated. As we shall soon see, it 

 accounts also for the rate of attenuation. 



In the particular configuration just described the electric component is 

 everywhere transverse, whereas the magnetic component may be either 

 longitudinal or transverse, depending on the point in a guide at which 

 observations are made. These waves are plane waves, but, since the elec- 



REGION OF LOW ATTENUATION 



Fig. 6.5-2. Relative phase velocity Vz and group velocity v' for various conditions of 

 operation of a waveguide. 



trie intensity is not uniformly distributed over the wave front, they are not 

 uniform plane waves. 



The concept of multiply reflected waves provides a basis for calculating 

 the attenuation in rectangular guides as was shown by John Kemp several 

 years ago.''' The procedure is outlined briefly below. The reader is referred 

 to the published article for details. 



There is shown in Fig. 6.5-3 a short section of hollow waveguide in which 

 we imagine multiply reflected plane waves are proj)agated. We fix our 

 attention on a zig-zag section cut from the guide and so directed that it 



'■' John Kemp, "Electromagnetic Waves in Metal Tubes of Rectangular Cross-section," 

 Jour. I.E.E., Part III, Vol. 88, No. 3, pp 213-218, September 1941. 



