A principle of multiport reflectometers is analysed with the Apollonius low re- flecting the symmetry.The transformation separation method to measure complex reflection co- efficient by means of four-pairs anti-phase unit-vectors is given.With this method

one can sen- sibly check up on the measurement error of the power detectors connected on the side-arm of the multiport reflectometers.This method not only can be used in the measuring technique of the four-port generalized reflectometer with amplitude response.but also can be used to cali- brate six-port reflectometer.