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4
RF Measurement Basics
Power Definition
In electrical circuits, power delivered to an electrical load can be defined as:
where
When the power is in the form of an AC waveform, a more complex definition is
needed. The cyclic power from the AC waveform varies with time. Although the
power of an AC waveform delivered at a specific time can still be defined using the
above formula, this does not adequately describe the AC waveform power
delivered to a load. Power of an AC waveform delivered to an electrical load is
equal to the mean power delivered over the course of one cycle of the sinusoidal
waveform defined by:
where
where
104
2
V
- - - - -
P
=
R
P is the delivered power.
V is the voltage applied to the load.
R is the resistance of the load.
T
(
(
(
P
=
V
cos
peak
0
T is the period of the AC waveform.
Evaluating the integral, we can reduce this expression to:
2
V 0
- - - - - - - -
P
=
R
V
is known as the root mean square (RMS) voltage of
0
the sinusoid.
V peak
- - - - - - - - - - - -
V 0
=
2
2
d
) T ⁄
)
)
⁄
2Πt
R
t
Keysight V3500A User's Guide
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