Getting Started 1
U2000 Series Operating and Service Guide 9
The U2000 Series USB Power Sensors in Detail
Most of the power sensors used for measuring average power employ
either thermocouple or diode technology. Diode- based sensors frequently
rely on the application of correction factors to extend their dynamic range
beyond their square law response region, typically from –70 dBm to
–20 dBm. While this technique achieves a wide dynamic range capability,
however, it is limited to continuous wave (CW) signals outside the square
law region. Modulated signals must be padded down or at low levels, with
their average and peak power levels within the diode square law region, to
be measured accurately. Accurate average power measurement of
high- level signals carrying modulation cannot be obtained using a CW
correction factor technique. Specialized modulation sensors are able to
provide accurate measurements but are limited by the bandwidth.
The U2000 Series USB power sensors are true average, wide dynamic
range RF/microwave power sensors. They are based on a dual sensor
diode pair/ attenuator/diode pair as proposed by Szente et. al. in 1990
1
.
Figure 1- 3 shows a block diagram of this technique.
Figure 1-3 Simplified block diagram of diode pair/attenuator/diode pair
1 US Patent #4943764, assigned to Hewlett-Packard Company
Low Sense
+
High Sense
+
High Sense
Low Sense
–
RF in
Lower Range
Upper Range
(
–7 dBm to +20 dBm)
(
–60 dBm to –7 dBm)
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