Multipath diode probes
What is Multipath diode probe?
Multipath diode probes
Multipath diode probes are special measurement sensors with a high dynamic range for power measurement of high-frequency signals. They contain multiple diodes connected with multiple power dividers to form a single calibrated unit.
A simple principle can be used for an RF power measurement: that of simple rectification using diodes, conversion to a DC voltage, and its display. After a temperature and frequency response correction, this DC voltage should be proportional to the power at the input of the measuring probe. Usually, two-way rectification is performed by measuring pairs of diodes. A disadvantage is that only a small range in the diode characteristic can be used for this because this characteristic has too large nonlinearities outside a small range (see Fig. 2). Thus the measurement setup with only one diode (or one pair of diodes) has a very low dynamic range.
Figure 2: Typical current/voltage diagram of Germanium and Silicium diodes
Figure 2: Typical current/voltage diagram of Germanium and Silicium diodes
The range used is the one that has a slope in the voltage characteristic in Figure 2 as in a quadratic function. The power is linear in this range, because the power is proportional to the square of the measured voltage.
Schematic
Multipath diode probes contain multiple diodes driven by several different power dividers. The RF power is split into several paths with different attenuation factors. Typically, two or three pairs of diodes are used and then the output of the diode pair operating in the favorable region of its characteristic is selected for display. In this way, a greater overall dynamic range is achieved, i.e. the power sensor has a greater measuring range than would be possible with a single diode pair. In practice, dynamic ranges very close to those of thermal sensors can be achieved in this way.
divider
Figure 3: Internal block diagram of a three-path diode sensor,
the dynamic range here is −70 dBm … +23 dBm in total.
In addition to the selection of the most favorable path, the task of the microprocessor includes the adjustment of the diode characteristics, an adjustment of the three paths to compensate for different gains and attenuations, as well as temperature compensation and frequency response correction.
Sources:
divider
Figure 3: Internal block diagram of a three-path diode sensor,
the dynamic range here is −70 dBm … +23 dBm in total.