Calibration of six-port reflectometers using null double injection

A new method for calibrating six-port reflectometers is presented. The method is based on the principle of ¿null double injection¿, a technique that consists of simultaneously driving the input and test ports of the reflectometer with sources whose relative amplitudes and phases are adjusted to produce nulls at the detector outputs. This six-port-to-four-port reduction technique permits the network constants to be determined simply from ratios of measured power at the remaining (unnulled) ports. Application of the technique to a prototype non-contacting reflectometer is demonstrated. The measurements of reflection coefficient for a set of loads taken by the prototype non-contacting reflectometer using this calibration method show good agreement with the ones by HP 8720C vector network analyzer, with measurement discrepancy less than 2% for 6 dB and 10 dB attenuators and less than 4% for the offset short over the frequency range from 1 GHz to 1.5 GHz.