The thru-reflection-unequal-line (TRuL) calibration method for scattering matrix measurement of multi-port networks

The multimode TRL calibration method is known as an approach for the measurement of multi-conductor transmission line devices. The propagation constants of different modes propagating along the multi-conductor transmission line must be different using this method. However, in general multi-port networks, the propagating constants at each port may be equal. We here then present the thru-reflection-unequal-line (TRuL) calibration method for the calibration of the equal propagation constant case. Lines of unequal length are used to make the eigenvalues unequal during calibration process. This will greatly simplify the calculation. The measured scattering matrix of a branch line coupler on FR4 substrate using proposed calibration method shows good agreement with simulation. This method can also be extended for the calibration of on-wafer and multi-port networks.