The French national metrology institute for time and frequency LNE-SYRTE has developed a new microwave satellite simulator to be used for the determination and monitoring of the delay difference in the Ku-band two-way satellite time and frequency transfer (TWSTFT) earth station. Such a device is more and more recommended by the CCTF working group on TWSTFT in order to better evaluate the ground station delay difference between two consecutive calibration campaigns. Besides few simulators commercially available and based on the VSL design, we have realized a new calibration device with at least two different concepts from those currently in use : a faster delay calibration process and a characterization of its internal delays using a microwave vector network analyzer (MVNA). The key component of this simulator is the use of a double-balanced microwave mixer and its characterization in terms of absolute delay; it requires a specific measurement system such as an MVNA allowing a vector mixer calibration technique with the use of a characterized mixer/filter as a through standard. The measurements and related uncertainties done with the MVNA are described in this paper. They are completed with those given by the SATRE modem during calibration sessions in order to perform the instability in noise of the whole system.