ETS-Lindgren 5411 GTEM! Test Cell - Manual (Page 36)

36 |
GTEM! Use
Estimation of GTEM! RF Input Power Required for Given Field Strength
The standard RF power-handling capability of the Model 5405 and Model 5407 is
in excess of 200 W. The standard RF power-handling capability of the
Model 5411 is 1000 W. Greater voltage or power-handling capabilities are
possible if modified feed sections, load boards, or optional blowers are installed.
Field intensities in excess of 200 V/m can be generated with sufficient
CW power.
Estimation of the power required for obtaining a given field strength is easy.
Using the parallel-plate electric field approximation, the estimated field strength
halfway between the septum and the floor of the GTEM! is given by the ratio of
the RF voltage on the septum to the spacing of the septum above the
GTEM! floor, or:
E(Volts/meter) = V (Volts) / h (meters)
RF voltage is obtained from the drive power by the equation:
P
in
(Watts) = V
2
(Volts
2
) / Z
o
(Ohms)
Where P
in
is input RF Power (Watts), V is RF voltage on the septum at height h,
and Z
o
is the GTEM! characteristic impedance (50 ohms).
Then a simple solution is:
 
2
1
0
1
Z P
h
 





 
 
0
2
Z
Eh
P

The previous equations can be used for first order estimates of field strength
given power, or power required for a given field strength. Power required
calculated by this method is approximate, and actual power needed for a given
electric field strength will vary versus frequency and location in the GTEM!.