Microwave reflectometer is an essential diagnostic tool with high spatial and temporal resolution for the measurement of plasma density profile. In recent years, a microwave reflectometry system has been developed and optimized on the J-TEXT tokamak. It consists of three parts: Q band (33-50GHz) with extra-ordinary mode (X-mode), V band (50-75GHz) with X mode and Q band with ordinary mode (O-mode). Its measurement range covers from the edge to core of the low field side plasma. To obtain a linear frequency sweep, the dynamic calibration of the voltage control oscillator (VCO) is completed. The profile measured by the reflectometer is in good agreement with the result of the polarimetry.

microwave reflectometer,dynamic calibration,density profile