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 of 0 to -60 dB. The following describes a subcarrier approach for extending the dynamic range of the dual six-port network analyzer. 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 +-0.05 dB or better, and an accuracy of +-0.16 dB or better at 3 GHz. Measurement results are also presented showing the dynamic range achievable with thermistor and barretter detectors. Key Words: barretter power detectors; diode power detectors; impedance measurements; microwave network analyze; six-port network analyze; thermistor power detectors.