ETS-Lindgren 3147 Log Periodic Dipole Array Antenna - Manual (Page 25)

The antenna factor of the Model 3147 (triangles) measured at the distance of
three meters as per ANSI C63.5. The standard states that the spacing R
between log-periodic array antennas is measured from the projection onto the
ground plane of the midpoint of the longitudinal axis of each antenna. This
midpoint has been marked on the radome and labeled Reference Point
Per ANSI C63.5. The line shown in the figure is a linear fit to the antenna factor
data. The second curve shows the gain of the antenna as computed from the
antenna factor by:
G(dB) = 20 log(F
MHz
) – 29.79 – AF
dB(m
-1
)
Typical Data | 25