The relation of calibration equations is investigated.It has been shown that for the reciprocal test fixtures
the four equations obtained from the measurement with a transmission standard can be used simultaneously in the calculation.Choices of the equations in the thru-short-match (TSM) and thru-reflect-line (TRL) methods are discussed.Experimental results show that the different choice of equations will lead to different solutions
and the calibration accuracy can be improved by utilizing the established relation of the calibration equations and properly choosing calibration equations.The proposed theory can be applied to the thru-open-match (TOM) and line-reflect-line (LRL) methods.