435 



One of the most important arrays is the linear multielement array where a 

 large number of equally spaced antenna elements are fed equal currents in 

 phase to obtain maximum directivity in the forward direction. Figure 18 gives 

 expressions for the radiation pattern of several particular cases and the general 

 case of any number of broadside elements. 



In this type of array a great deal of directivity may be obtained. A large 

 number of minor lobes, however, are apt to be present, and they may be unde- 

 sirable under some conditions, in which case a type called the binomial array 

 may be used. Here again all the radiators are fed in phase but the current is not 

 distributed equally among the array elements, the center radiators in the array 



A ■= 1 for horizontal loop, vertical dipole 



A = 



(I*") 



for horizontal dipole 



cos 



s° = spacing of successive elements in degrees 



Fig. 18. — Linear multielement array broadside directivity. 



being fed more current than the outer ones. Figure 19 shows the configuration 

 and general expression for such an array. In this case the configuration 

 is made for a vertical stack of loop antennas in order to obtain single-lobe 

 directivity in the vertical plane. If such an array were desired in the horizontal 

 plane, say n dipoles end to end, with the specified current distribution the 

 expression would be 



F(0) = 2"" 1 |~ cos tt/2 sin f \ CQS n-i (1/2 S ° sin #) 

 L cos 6 J 



The term binomial results from the fact that the current intensity in the suc- 

 cessive array elements is in accordance with the binomial expansion (1 + l) n "\ 

 where n is the number of elements. 



{continued) 



SMITHSONIAN PHYSICAL TABLES 



