Characterisation of RF diode power sensors
Today different types of diode power sensors become increasingly important for various applications and set new demands for calibration laboratories.
Two NMIs participate in this comparison of radio frequency (RF) diode power sensors. The measurands of interest are the calibration factors at 4 different power levels in the frequency range of 50 MHz to 18 GHz as well as the linearity in the power range of 1 µW to 20 mW at the two frequencies 50 MHz and 1 GHz. In addition, the complex input reflection coefficient has also to be characterized at different power levels.
To our knowledge no comparisons have been conducted so far for the mentioned quantities. This first comparison offers the participants the possibility to verify their measurement procedures including the evaluation of measurement uncertainty.
The measurement standard is a diode power sensor type NRV-Z1 (R&S) and a power meter type NRVS (R&S) for the readout of the sensor. The devices are provided by SP.
Pilot duties are shared among SP and METAS. SP does the analysis of the data while METAS writes all the reports and acts as coordinator in this project. For details see the Technical Protocol.
Final Report 2010-04-12
The project has been completed and the report can be downloaded here>>
Today RF diode power sensors of various types become increasingly important for many applications and set new demands for calibration laboratories. Such sensors offer an increased dynamic range compared with thermal sensors but they require internal linearity corrections. Furthermore, properties like linearity and input reflection are frequency dependent. Therefore, a calibration system for diode power sensors is more complex compared to a system for thermal power sensors. This first bilateral comparison offered the participants the possibility to verify their measurement procedures and it provided a possibility to find and fix errors.
The calibration factor (Normalized Frequency Response), the linearity (Level Dependent Calibration Factor) and the complex input reflection coefficient of a diode power sensor were compared.
Besides the good agreement in all results between the participants the following comments can be made:
This first diode power sensor comparison helped to improve the measurement procedures at both labs.
The measurement of the calibration factor was based on the conventional direct comparison method at both laboratories but required additional efforts to create the different power levels and to control the harmonic content of the signal source. With a carefully designed setup it is possible to achieve measurement uncertainties of the same order of magnitude as with thermal power sensors. This is even true for power levels below 1 mW.
The linearity (Level Dependent Calibration Factor) was evaluated by each participant applying different setups. The results agree and the resulting measurement uncertainties are considerably lower than for the frequency dependent calibration factor.
For the calibration factor and linearity characterization of diode sensors it is important to keep harmonics of the test signal at a low level, otherwise they can contribute considerably to the total measurement uncertainty.