ETS-Lindgren 3145BDP Dual-Polarized Log-Periodic Dipole Array - Manual (Page 17)

Practical Application | 17
4.0 Practical Application
Horizontal and vertical polarizations are easily accomplished with the
Model 3145BDP. Due to the length of the low-frequency elements, users should
verify element clearance prior to switching the antenna to vertical polarization.
Contact with any metal or non-metallic structure can capacitively load the
antenna which may cause inconsistent results. Make sure that no part of the
dipole elements are in contact with the tower, particularly in vertically-polarized
tests. Where possible, run the feed cable straight back at least one meter or
more from the Model 3145BDP before dropping vertically.
For emissions measurements, electric field strength in dB[V/m] is obtained from:
( ) ( ) ( ) ( )
E V AF dBV / m dBV dB1 / m dB
= + + α
V = receiver or spectrum analyzer voltage reading
AF = antenna factor
α
= cable loss, if cable losses are non-negligible
For immunity testing, the electric field strength generated at a distance d can be
approximated by:
( )
E
pg
d
V / m
=
30
d = in meters
g = numeric gain (10G[dB]/10)
p = antenna net input power, in watts
Actual transmitted field strength should be verified using an ETS-Lindgren
HI-6005 electric field probe, or equivalent. For IEC 1000-4-3 testing, the antenna
tip can be placed at any distance between one and three meters from the EUT as
long as the reference plane is illuminated according to the 0, +6 dB uniform field
specification. In general, closer distances require less power to create a given
field strength.