WAVEGUIDE TRANSMISSION 



325 



Thus far, we have restricted our considerations to directivity in the plane 

 of the two conductors (vertical plane as here assumed). Experiment shows 

 that, in the plane perpendicular to that illustrated, the directivity from a 

 single pair of wires is slight. However, we may obtain additional directivity 

 by increasing the horizontal aperture. One method of accomplishing this 

 result is to array, at rather closely spaced intervals, identical elementary 

 radiators each of the kind just described. [See Fig. 6.3-4(a).] An infinite num- 

 ber of these elements infinitesimally spaced become two parallel plates as 

 shown in Fig. 6.3-4(b). If metal plates are now attached at the right and left 



(a) 



(b) 



Fig. 6.3-3. Illustrating how radiating systems of large aperture may give rise to wave fronts 

 of large radius of curvature and hence lead to increased directivity. 



(a) (b) 



Fig. 6.3-4. Alternate ways by which the aperture of a flared transmission line radiator may 



be increased. 



sides, the resulting configuration will become a waveguide horn. As a general 

 rule, the larger the area of aperture, the more directive will be the antenna. 

 The highly schematic array shown in Fig. 6.3-4(a) is introduced for illustra- 

 tive purposes only. It is not one of the preferred forms used in microwave 

 work. More practicable forms will be found in Chapter X. 



The wave model shown in Fig. 6.3-2 conveys but a portion of the known 

 facts about a radiated wave. A more accurate model is shown in skeleton 

 form in Fig. 6.3-5. It is assumed that the transmitted wave has been launched 

 with about equal directivity in the two principal planes and that the ob- 



