A technique for extending the dynamic range of the dual six-port network analyzer

The dynamic range of the six-port type of automatic network analyzer is typically limited to measuring two-port devices with a transmission coefficient S12 in the range 0 to -60 dB. A subcarrier approach for extending the dynamic range of the dual six-port network analyzer is described. The subcarrier is generated by inserting a 10-kHz biphase modulator ahead of one of the six-ports. With the subcarrier approach, measurements of S12 in the range of -60 to -100 dB can be made. Test results are presented showing measurements of S12 = -80 dB with a precision of + or - 0.05 dB or better and an accuracy of + or - 0.16 dB or better at 3 GHz. Measurement results are also presented showing the dynamic range achievable with thermistor and barretter detectors.