Appendix A - Calculating Calibration Factors - Advanced Energy 2818A User Manual

Appendix A - Calculating Calibration Factors

When using an RF Power Meter with an RF Power Sensor to make an RF Power Measurement
the user must know that the measurement is accurate and there is traceability to a known
standard. All diode, thermo-electric, and thermistor power sensors have calibration factors
associated to frequencies that are used to insure an accurate power measurement. Technicians and
engineers use these calibration factors when making measurements, but where do these
calibration factors really come from?
During calibrations, calibration factors are transferred from a terminating reference to a feed-
through (transfer) standard, and then into the DUT. In some procedures, this transfer occurs all in
one session, and in others time is saved by transferring into the feed-through once and then using
that feed-through calibration to calibrate DUT's for some time.
Calibration factors of a terminating power sensor relates standard RF power to the total RF power
incident on the sensor being used. For this purpose, incident means all the RF propagating
toward the sensor reference plane, including power that is subsequently reflected. On the signal
flow diagram (figure 4), the incident power is ��
Calibration factor of a feed-through power calibration setup relates the standard's RF power to
the power delivered out of the DUT port into a load of exactly the nominal characteristic
impedance of the system, or ��
leveled generator, then the output into a perfect load is ��
So, for a terminating sensor (using the "M" subscript):
And for a feed-through standard, (using the "F" subscript):
Where:
k Calibration factor of the Terminating Mount
M =
k Calibration factor of the Feed-through Mount
F =
P = Power measured terminating mount
SubM
P = Power measured Feed-through mount
SubF
2818A-900 Revision AB
= | ��
��
. If we think of the feed-through DUT port as the output of a
0
��
��������
�� =
��
��
��
��
��������
�� =
��
��
��
��0
RF Power Transfer Standard
2
.
|
��
.
��
��0
6
18