The far field is approximately given by
In general we are going to use a current pulse defined as 
with 
and 
as the step function. Here n
represent the number of oscillations during the decay time scale 1/
. We chose the decay parameters as 
s
and 
s
, hence 
, which correspond to
realistic parameters for lightning [Uman, 1987].
As a measure of the amount of energy radiated to a given point in the far
field, we can define an array factor as 
From Eq. (12 ) we can write this array factor as
where 
corresponds to
the parameters from the beginning (i) of the line element, and similarly for
the endpoint (f). Also 
and I
is the current strength
of the n
element. The array factor can be normalized by maximum in
the array factor corresponding to the single dipole, i.e.,
where 
with 
as the difference in
distance between the beginning and end points of the dipole to the detector
position. h is the height of the detector.
