ANTENNA ARRAYS 



35 



1. Broadside. Here s = X/2, the currents are in 

 phase (^ = 0°). The maximum field is broadside and 

 twice that of each dipole. 



3.4.4 



^ V ^ 



EQUATORIAL PLANE 



cos 9 



Figure 27. Two half-wave dipole colinear array. 



Two-Dipole 

 Colinear Arrav 



For two equal currents in time phase (see Figure 

 27), the field is equal to 



60/ 



cos 



(^cose) 



. a 



.sin 2 



where 



27r 



a = — s COS 



X 



(23) 



(24) 



The field is circularly symmetrical about the axis. 

 Its variation with d is plotted in Figure 28. This is, 

 of course, equivalent to a vertical antenna with 

 center height at distance •s/2 abo^'e a perfectly 

 conducting flat earth. 



2.0 



1.0 1.0 



s=(l/2)X 



2.0 1.0 1.0 



s=(3/2)X 



2.0 



2.0 1.0 1.0 2.C?° 2.0 1.0 q 1.0 2.C?° 



S3 IX S=2X 



Figure 28. Two half-wave dipole colinear array. 



2. End-fire. Again s = X/2, but the currents are 

 out of phase (^ = 180°). The maximum field is 

 found in both directions along the line of centers. 



3. Unidirectional couplet. Here s = X/4 and I« 

 lags Iihy\p = 90°. The result of this combination 

 is to produce a maximum field along the Hne of 

 centers in the direction looking from the leading to 

 the lagging current and zero field in the reverse 

 direction. 



3.4.5 



One-Dimensional Array 



Two geometrical arrangements will be considered. 

 1. Broadside. Consider n elements \\dth equal co- 

 phased currents equally spaced (see Figure 29) . 



sm- 



na 



Ee=E,i{d,cf>) 



(25) 



sm 



