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Design and testing of a software feedback loop for RF power leveling



Xiaohai Cui, Thomas P. Crowley


We have developed a software feedback loop that stabilizes the RF power input in calorimetric measurements to better than 30 ppm. In this system, a bolometric sensor with a Type IV power meter is used to detect the power. Feedback is provided to the AM input of an RF generator through a computer-controlled voltage source. The software feedback loop replaces an analog feedback loop that used a NBS Type II Power Measurement System to provide the AM input signal. The new system removes a potential error in the DC substituted power that is caused by loading of the Type IV when it is connected to the Type II. The new leveling system is more flexible than the previous system and it is easy to modify the desired leveling accuracy and real-time feedback rate. The design and evaluation of the software leveling system is presented. It has been tested using the WR-15 microcalorimeter which will be the national standard for power in the US from 50 to 75 GHz.
Proceedings Title
Conference Dates
December 11-12, 2008
Conference Location
Portland, OR


RF power, microwave power, bolometer, Type IV power meter


Cui, X. and Crowley, T. (2008), Design and testing of a software feedback loop for RF power leveling, ARFTG 72nd MICROWAVE MEASUREMENT SYMPOSIUM, Portland, OR (Accessed July 14, 2024)


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Created December 12, 2008, Updated February 19, 2017