An automated calibration unit has several ports for connecting with respective ports of a test and measurement instrument to be calibrated. The automated calibration unit has a frequency conversion circuit that is non-linear and reciprocal in amplitude and phase. The automated calibration unit has at least one switching circuit with several switch states. The automated calibration unit is configured to selectively connect each one of the several ports to another one of the several ports depending on the switch state, thereby providing a through connection via the frequency conversion circuit. The automated calibration unit is configured to selectively connect each one of the several ports to at least one of several calibration standards respectively depending on the switch state. Further, a frequency conversion circuit and a method of performing calibration of a test and measurement instrument are described. Moreover, a method of absolute power calibration transfer is described.