Introduction 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
(
–10 dBm to +20 dBm)
(
–60 dBm to –10 dBm)
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