356 PROPAGATION THROUGH THE STANDARD ATMOSPHERE 
gives the directional characteristic of the element The field is circularly symmetrical about the axis. 
itself. Its variation with 6 is plotted in Figure 28. This is, 
of course, equivalent to a vertical antenna with 
a> Ses ASS AB : 
if x Z Z \ center height at distance s/2 above a perfectly 
tl Ip o><el, ! = OF \ conducting flat earth. 
\ / i 
> pe Se oH See 4 ° 
BROADSIDE END-FIRE UNI-DIREC TIONAL 
$=/2 S=)/2 S=/4 
w= 0° Y=180° W=90°C IZ LAGS I) 
EQUATORIAL PLANE §=90° 
Figure 26. Radiation patterns (field strength) for two 
dipole side-by-side array. 
Three special cases are particularly to be noted. 
The field patterns for the equatorial plane (@ = 90°) 
and | I, | = | I: | are plotted in Figure 26. 
1. Broadside. Here s = d/2, the currents are in 
phase (y = 0°). The maximum field is broadside and 
twice that of each dipole. 
2. End-fire. Again s = \/2, but the currents are 
out of phase (y = 180°). The maximum field is 
found in both directions along the line of centers. 
3. Unidirectional couplet. Here s = /4 and Ip 
lags I, by y = 90°. The result of this combination 
is to produce a maximum field along the line of 
centers in the direction looking from the leading to 
the lagging current and zero field in the reverse 
direction. 
iy 
THe 
Two-Dipole K \ SP, ° 
Colinear Array QDS 75 
Zum e 
For two equal currents in time phase (see Figure 2.0 1.0 fo) 1.0 2.0 
27), the field is equal to s=(3/2)d 
Tv ° 
cos (> cos 6 sin a Oo 1S 6 
ig | : o Gy ||? ) Waligh 5 
sin 6 sin = 
2 
where 
2 
a= —scos#. (24) 
nN 
et s=2a 
ee Figure 28. Two half-wave dipole colinear array. 
One-Dimensional Array 
: Two geometrical arrangements will be considered. 
h 1. Broadside. Consider n elements with equal co- 
imuess phased currents equally spaced (see Figure 29). 
s Ce EQUATORIAL PLANE sin > 
er Bak ees Eo= Ea (6, ?) ; (25) 
(ime NO sin — 
ry \s cos@ 2 
where 
a= = S$ cos g. (26) 
Figure 27. Two half-wave dinole colinear array. 
