Technology On 26.5GHz-40GHz National Power Standard's Measurement

The millimeter wave power standards are very important in providing the national measurement capacity and traceability. The main research is based on the project of WR28(26.5G～40GHz) power standard which was set up last year.Firstly the principle of the calorimeter used in the project is described. Secondly, the paper introduced three major aspects:the calorimeter, the power measurement and control circuit and power value transfer system. The calorimeter uses self-developed waveguide calorimeter. Details of its structure are introduced. The characters in power measurement and control circuit including "zero temperature", "high temperature sensitivity of the bridge", "partial DC substitution" and "adaptive gain control" are analyzed. In addition, the process of power transfer is explained.The calorimeter's effective efficiency is analyzed and derived. To obtain it, substitution efficiency and equivalent source reflection efficiency associating with it are needed to be accurately determined.RF power which worked on the load was substituted by DC power heating the resistances, these resistances was pasted on the surface of the absorber of the RF load. Components of substitution efficiency can be obtained with the experiment, meanwhile microwave power distribution of the absorber in the calorimeter can be simulated by the electromagnetic simulation software. So the substitution efficiency can be derived by combing them.The experiments, with three kinds of methods of equivalent source reflection efficiency including traditional method, the direct calibration method and K.Shimaoka method recently proposed by K.Shimaoka were done, the results and comparision show that K.Shimaoka method is the best choice in WR-28 power standard system due to its comprehensive advantages including rigorous theory, simply operation approach and accuracy.