Self calibration apparatus and methods

In one method of calibrating an instrument having N ports, where N>=2, cables of a first type are characterized by connecting a first cable between two of the ports; performing an "unknown-thru" full two-port calibration between the two ports; obtaining a S-parameter of the first cable; saving the S-parameter of the first cable; and then repeating the connecting, performing, obtaining and saving for additional cables having the first type. The cables having the first type are then disconnected from one of the two ports and a measurement plane is transferred from the connected end of the cable to the disconnected end of the cable. Cables of a second type are then characterized by connecting a second cable between the second of the two ports and the disconnected end of the first cable; measuring a S-parameter of the second cable; and saving the S-parameter of the second cable.