ANTENNAS 
for the unidirectional broadside and colinear arrays 
are given in Figure 34. 
The broadside array is a collection of unidirec- 
tional couplets of the type illustrated in Figure 26. 
Increasing the number of couplets n appreciably 
narrows the beam width. 
A similar improvement is obtained in the colinear 
combination. 
| 
B —{ah— (B) Colinear 
Fi@ure 34. Unidirectional broadside and colinear array. 
Multidimensional Arrays 
Enough has already been given to show that itis 
not difficult to extend the principles of summation 
of fields from elements to cover two- and three- 
dimensional arrays. 
Binomial Arrays 
Most array patterns show, in addition to the main 
maximum, secondary maxima (side lobes) which are 
inconvenient in radar work. Side lobes are practi- 
cally eliminated in the binomial array. 
Consider first a two-element half-wave dipole 
broadside array with equal cophased currents and 
elements spaced a half wavelength apart. See equa- 
tions (21) and (22). Theny = 0, s = X/2, a = rcos¢. 
Then with 
601 coe( Fens a) 
139 (OY SS Se ES 
NO ere rer 5) 
E = By (e? + e7*). 
This gives the broadside field in Figure 26 which has 
only two.equal major lobes. There are no side lobes. 
359 
Now consider the equation 
E = By (+ ¢*)?, 
= Ey (1 + 2e + 16). 
(36) 
This represents three half-wave dipoles in broadside, 
spacing s = \/2, currents in phase but with relative 
magnitudes 1 :2:1. The pattern has no side lobes. 
Again, for five similar dipoles, 
E = Ey (e” + e**) ; (37) 
= Ey (1+ 46% + 66 + 46% 4 6-742), 
Here the cophased current magnitudes are 1:4: 
6 : 4:1, and there are no side lobes. 
The scheme is to follow the pattern of binomial 
coefficients in adjusting the relative current values. 
m=1 yl 
2 i Py al 
3 i a 8 i 
4 14 6 41 
5 15101051 
Tach number is the sum of the two immediately 
above. 
Ring Arrays 
A set of radiating elements can be arranged on the 
perimeter of a circle with equal angular distances and 
equal phase shift between the elements; the diameter 
of the ring must be properly chosen; the resulting 
radiation pattern can be made very nearly uniform, 
1.e., circular, in the plane of the ring, while the 
Figure 35. Ring array. 
directivity of the pattern obtained in a plane per- 
pendicular to that of the ring is increased compared 
to that of the single element. 
If a number of such rings are stacked on top of each 
other with a common vertical axis, a linear array is 
formed whose elements are the rings. A radiation 
pattern is thus produced that has pronounced direc- 
tivity in elevation while it is nearly uniform in 
azimuth. This is often used in micro wave beacons. 
