PMX40 RF Power Meter – INSTRUCTION MANUAL
5-3
averaging, the Model PMX40 has additional capabilities that allow it to perform statistical analysis on a
complete set of continuously sampled data points. Data can be viewed and characterized using a CCDF
presentation format. These analysis tools provide invaluable information about peak power levels and
their frequency of occurrence, and are especially useful for non-repetitive signals, such as those used in
5G and Wi-Fi applications.
5.1.2
Diode Detection
Wideband diode detectors are the dominant power sensing device used to measure pulsed RF signals.
However, several diode characteristics must be compensated to make meaningful measurements. These
include the detector’s nonlinear amplitude response, temperature sensitivity, and frequency response
characteristic. Additional potential error sources include detector mismatch, signal harmonics, and
noise.
Detector Response
. The response of a single-diode detector to a sinusoidal input is given by the diode
equation:
𝑖𝑖
=
𝐼𝐼
𝑠𝑠
(
𝑒𝑒
𝛼𝛼𝛼𝛼
−
1)
where:
i = diode current
𝑣𝑣
= net voltage across the diode
I
s
= saturation current
𝛼𝛼
= constant
An ideal diode response curve is plotted in Figure 5-3.
Figure 5-3.
Ideal Diode Response
The curve indicates that for low microwave input levels (Region A), the single-diode detector output is
proportional to the square of the input power. For high input signal levels (Region C), the output is
linearly proportional to the input. In between these ranges (Region B), the detector response lies
between square-law and linear.
For accurate power measurements over all three regions illustrated in Figure 5-3, the detector response
is pre-calibrated over the entire range. The calibration data is stored in the instrument and recalled to
adjust each sample of the pulse power measurement.
