Specifications

EMC-CS-2009.1
© Copyright Ford Motor Company – All Rights Reserved Page 95 of 121
February 11, 2010
p) For each frequency below 10 fs, verify that the chamber meets the field uniformity requirements by the following
procedure:
q)
Field uniformity is indicated by the standard deviation from the mean value of the maximum electric field values
obtained at each of the probe location during one complete rotation of the tuner. This standard deviation is calculated
from data for each probe axis independently and the total data collected.
r)
The standard deviation is the following:
1n
EE
ασ
2
i
−
∑
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−
∗=
tt
Where:
i = 1, 2, to 8 (number of probe locations)
n = Number of measurements
i
E
t
= Maximum normalized electric field probe measurement
E
t
= Arithmetic mean of the normalized electric field measurements
α = 1.06 for n ≤ 20 and 1 for n > 20
σ = Standard deviation for a given axis (x, y, or z)
Example for the x-axis
()
18
EE
06.1σ
2
xix
x
−
∑
−
∗=
tt
Where:
i = 1, 2, to 8
ix
E
t
= Maximum normalized electric field probe measurement of x axis
x
E
t
= Arithmetic mean of normalized axes from all eight measurement locations
Example for all axes:
124
EE
1σ
2
24
z,y,ix
24
−
∑
⎟
⎠
⎞
⎜
⎝
⎛
−
∗=
tt
Where i = 1, 2, to 8
zyix
E
,,
t
= Maximum normalized electric field probe measurements of all axes (x, y, and z)
24
E
t
= Arithmetic mean of normalized Emax x, y, z axes from all 24 measurements
σ
24
= Standard deviation of all axes (x, y, and z)
The standard deviation is expressed in terms of dB relative to the mean:
()
z,y,x
z,y,x
E
Eσ
log20dBσ
t
t
+
∗=