434 TABLES 453-465.— RADIO PROPAGATION DATA * 



Antenna arrays (figs. 17-19). — The basis for all directivity control in an- 

 tenna arrays is wave interference. By providing a large number of sources of 

 radiation, it is possible with a fixed amount of power greatly to reinforce radia- 

 tion in a desired direction by suppressing the radiation in undesired directions. 

 The individual sources may be any type of antenna. 



The radiation patterns of several common types of individual elements are 

 shown in figure 17. The expressions hold for linear radiators, rhombics, vees, 

 horn radiators, or other complex antennas when combined into arrays, pro- 

 vided a suitable expression is used for A, the radiation pattern of the individual 



= horizontal angle measured from perpendicular bisecting plane 

 /3 = vertical angle measured from horizon 

 K and K' are constants and K' = 0.7K 



Fig. 17. — Radiation patterns of several common types of antennas. 



antenna. The array expressions are multiplying factors. Starting with an in- 

 dividual antenna having a radiation pattern given by A, the result of combining 

 it with similar antennas is obtained by multiplying A by a suitable array factor, 

 thus obtaining an A' for the group. The group may then be treated as a single 

 source of radiation. The result of combining the group with similar groups, or, 

 for instance, of placing the group above ground, is obtained by multiplying A' 

 by another of the array factors given. 



The expressions given here assume negligible mutual coupling between in- 

 dividual antennas. When coupling is not negligible, the expressions apply only 

 if the feeding is adjusted to overcome the coupling and thus produce resultant 

 currents that are of the amplitude and relative phases indicated. 



* Data arranged by Newbern Smith and Marcella Phillips, Central Radio Propagation 

 Laboratory, National Bureau of Standards. 



(continued) 



SMITHSONIAN PHYSICAL TABLES 



