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Average Pulse Power Measurement Demonstration
Pulse power is determined by measuring the average power of the pulse and then dividing the measurement results by
the pulse-cycle value to obtain the pulse power reading, as expressed by the following equation:
The measurement result is a
mathematical representation of the
pulse power rather than the actual
measurement with the assumption
of constant peak power. To ensure
accurate pulse power readings, the
input signal must be a repetitive
rectangular pulse with a constant
duty cycle.
There are some advantages to using
duty cycle to calculate the pulse
power. The duty-cycle technique
provides the lowest-cost solution,
with average power meters and
sensors being less expensive than
peak and average power meters and
sensors. Average power meters also
have the ability to measure over a
wide power and frequency range.
In this demonstration, we are
supplying a pulsed signal with the
pulse width of 20 μs and a pulse
period or pulse repetition interval
(PRI) of 40 μs. The pulse signal is set
to the power level of approximately
0 dBm. (See Figure 3).
Using a V3500A handheld power
meter to measure the average power
of the signal, the measurement result
is –3.04 dBm. We can see from
the results that the average power
over the full PRI is –3.04 dBm lower
than the pulse itself. The measured
value is therefore very close to
the calculated –3.01 dB difference
provided by the duty-cycle method,
which was for the 'perfect' pulse
shape.
P
avg
P
in linear term. (See Figure 2)
=
p
Duty Cycle
Power
Figure 2. Pulse power calculation
Figure 3. Measuring pulse power using duty cycle
B (Pulse Repetition Interval)
A
Duty Cycle
B
A (Pulse Width)
Average Power Δ = 10 log DC
Pulse Width
(PW)
Pulse Repetition Interval (PRI) = 40 µs
6
Measured
Average Power
Time
= 10 log (20 µ/
40 µ)
= 10 log 0.5
= –3.01 dB
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