CLIENTS user guide SA1000
Page 15
Individual plots for each location in EUT volume (Cell020)
0
10
20
30
40
50
60
70
0
100 200 300 400 500 600 700 800 900 1000 1100
Frequency (MHz)
O
u
tp
u
t
(d
B
)
Figure 6. Measurements of the ERS at 12 locations in one quadrant of the test volume.
The
’
antenna factor
“
(A.F.) or
’
correction data
“
or calibration factor
“
can be calculated for each
location by using the calibration data for the ERS.
At each 2MHz frequency step:
AF(cell) = ERS(dB) - cell(dB)
So if the ERS has been measured as 56dBuV/m on the NPL 3 metre test site, and the ERS is
measured as 62dB in the test cell, then the cell A.F. is 56 - 62 = -6dB.
Figure 6 shows how especially at higher frequencies, some locations give different results. This
is a common feature of GTEM and similar cells. It happens when the wavelength becomes
comparable with the physical dimensions of the cell. In particular note how narrow
’
dropouts
“
occur when the cell effectively becomes less sensitive. These represent small
’
dead
“
zones in the
test volume. The standard technique to ensure that these do not cause significant measurement
errors is to scan the EUT several times, each scan with the EUT is a different location. The final
result is taken as the peak reading at each frequency step across all the scans.
To calculate the cell calibration, the following procedure is used:
For each frequency step....
List all 12 measurements (corresponding to the 12 locations) and discard the 4 lowest.
Average the 4 highest readings.
Check that the highest reading is within 4dB of the average.
Using the average and the ERS data, calculate the A.F. of the cell.
