B+K precision RFM3000 Series, User Manual, Page: 44 / 58

Application Notes 44
5.1.2 Diode Detection
Wideband diode detectors are the dominant power sensing device used to measure pulsed RF signals. Several diode
characteristics must be compensated to make meaningful measurements. These include the detector’s nonlinear ampli-
tude 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:
𝑖 = 𝐼
𝑠
(𝑒
𝑎𝑣
− 1)
where:
𝑖 = 𝑑𝑖𝑜𝑑𝑒𝑐𝑢𝑟𝑟𝑒𝑛𝑡
𝑣 = 𝑛𝑒𝑡𝑣𝑜𝑙𝑡𝑎𝑔𝑒𝑎𝑐𝑟𝑜𝑠𝑠𝑡ℎ𝑒𝑑𝑖𝑜𝑑𝑒
𝐼
𝑠
= 𝑠𝑎𝑡𝑢𝑟𝑎𝑡𝑖𝑜𝑛𝑐𝑢𝑟𝑟𝑒𝑛𝑡
𝛼 = 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.