WAVEGUIDE TRANSMISSION 



339 



lies parallel to the direction of propagation of the elemental wave fronts. 

 The top and bottom conductors so formed may be regarded as a uniform 

 flat-conductor transmission line with oblique reflecting plates (sections 

 of the side walls) spaced at regular intervals. Other transmission lines 

 adjacent to that under consideration behave in exactly the same way as 

 that singled out for examination and at the same time act as guard plates 

 to insure that the lines of force so propagated remain straight. 



It is clear that the attenuation in each elemental transmission line will 

 be that incidental to losses in the upper and lower conductors plus the 

 losses incidental to reflection at oblique incidence from the several reflecting 



Fig. 6.5-3. Elementary transmission lines terminated periodically by reflecting plates 

 which go to make up a rectangular waveguide. 



plates. The total attenuation of the rectangular guide may then be found 

 by summing up over a unit length of waveguide all of the elemental lines. 

 This has been done with results that are equivalent to the corresponding 

 equations given in Chapter V. The results are plotted in Fig. 6.5-4. 



Certain characteristics of these curves may be readily accounted for. 

 For instance, at cut-off (6 = 0), both the number of unit reflection plates 

 and the number of flat-plate transmission lines in a given length of wave- 

 guide will be infinite. As a result, the component attenuations arising in 

 each of these two sources will likewise be infinite. As the frequency is in- 

 creased above cut-off the angle 9 will increase accordingly, leading thereby 



