ANTENNAS 355 
Figure 24 illustrates the radiation. pattern. (relative parallel to each and perpendicular to the line. With 
field strength) for a particular case. the currents adjusted all in phase, the maximum 
radiation is broadside to the plane of the elements. 
ANGLE IN DEGREES 2. End-fire array. The geometric arrangement is 
90 70 50 40 30 20 the same as in the broadside array, but through 
6 appropriate phasing of the currents in the elements 
the maximum radiation can be directed primarily 
along the line joining the centers. 
3. Colinear array. Here the axes of the antenna 
elements are arranged along the line of centers with 
iN 
! 
1 
O PLAN VIEW 
SS 
SS 
SF 
Z 
ISS 
LN i 
aes BS ‘ the currents all in phase. The radiation is a max- 
1 2 3 $+72.5° imum in the equatorial plane perpendicular to the 
ANGLE IN DEGREES « =17,5° 
line of centers. 
20 To illustrate the principles most simply, two half- 
ie wave dipole elements are considered first, and later 
ELEVATION . . 
extension is made to arrays composed of a larger 
number of elements. 
90 70 60 50 40 30 
Two-Dipole Side-by-Side Array 
Figure 24. Rhombic antenna above ground (relative 
field strength). (Courtesy of Bell System Technical Two half-wave dipoles are placed side by side with 
Journal.) spacing s and the currents J; and J; are equal but 
differ in phase by angle p (see Figure 25). If J, lags 
I, by time angle y, the field of the second element 
at P lags that of the first by angle a where a is 
ANTENNA ARRAYS 
Principle of Arrays 
H 
¢ eone™ 
An antenna array is a combination of several 
antennas, usually of equal strength and equally 
spaced in any one given direction. One-, two-, and 
three-dimensional arrays may be distinguished. The 
spacings in different directions may be different for 
two- or three-dimensional arrays. The use of arrays 
permits great increases in the amount of power 
radiated, in directivity, and gain. 
Although the most common array element is a 
half-wave dipole, the elements of an array may be 2 eer Ve ALE NAUNSO SSN Ms eR LD 
radiators of any type; in particular, the elements prauull EQUATORIAL PLANE, 9= 7/2 
may themselves be arrays. In this way it is possible 
to interpret a two-dimensional array as an array of 
arrays. A vertical curtain may be considered either 
as a horizontal array of elements which, themselves, 
are vertical, or it may be considered a vertical array 
Figure 25. Two dipole side-by-side array. 
composed of y and the time delay caused by the 
extra distance traveled, (27/))s cos @ sin 6, 
of elements which, themselves, are honizontal arrays; a = + (27/)) scos@ sin 8. (21) 
similarly for three-dimensional arrays. 
In most arrays the elements radiate very nearly For equal currents, I; = I, = J, the field is equal 
equal power, but in the binomial array the elements, to 
although identical in structure, differ in the amount 
of power radiated because of differing current dis- [ | [eas G ee s) | 
tributions. In most arrays there is a constant phase Bs GOT) 6 + 7 2 A 
shift (which might be zero) between adjacent ele- i d [ sin 6 | 
ments. By suitable phasing a great variety of an- i 
tenna patterns can be produced. sin a cos{ =cos 6 
ie cor| eu on ( peo) | : (22) 
h Basic Types of Dipole Arrays [ sin sin 6 
i) There are three basic types of dipole arrays. 
4 1. Broadside array. The centers of the elements The first bracket gives the directional characteristic 
are arranged in a line, with the axes of the elements of an array of two elements, while the second bracket 
