- 4 -
1 - Stacking Yagis
In-phase
The greatest gain increase comes from the
first pair of antennas.
Optimum spacing is usually around one-
wavelength stack spacing.
Lower heights produce a cleaner pattern.
Avoiding nulls in the middle of useful
propagation angles is often more important
than a small gain improvement.
Note that increased heights result in maximum
stack gain improvement (maximum gain still
occurs at about 1 wavelength antenna-to-antenna
spacing) and lower wave angles. The lowest
antenna should generally be significantly higher
than the antenna-to-antenna spacing above ground
for maximum stacking gain. Greatly increased
height produces more minor lobes and stronger
minor lobes.
Neglecting feedline losses, over medium soil two
stacked Hy-Gain model 205CA 20 meter antennas
have the following in-phase gain improvement:
Figure 1
70 feet = 1 wavelength
Height
35+70 ft
52+104 ft
70+140
Optimum
87.5+175
110+180ft
Gain/ angle
15.41dBi
@15 deg
16.89 dBi
@11 deg
17.27dBi
@ 8 deg
17.17
@7 deg
17.87 dBi
@ 6 deg
Stack spacing
0.5 wave
.75 wave
1 wave
1.25 wave
1 wave
Reference
Figures
Figure 1
Figure 2
Figure 3
