Attached is a 1998 write-up by R. H. Siemann of the Stanford Linear Accelerator Center which shows how the SR830 Lock-In Amplifier (1 milliHz-102.4 kHz) can be configured with other test instruments to perform the function of a VNA at W-band frequencies. From my cursory reading of Lock-In Amplifiers, I understand that they are able to measure very small signals in the presence of overwhelming noise. Today’s best instruments have a dynamic reserve of 120 dB, meaning they can accurately measure a signal in the presence of noise up to a million times higher in voltage amplitude than the signal of interest! Upon noting this astounding capability, my immediate question is as per above: Does a Lock-In-Amplifier-based-VNA have better sensitivity than a conventional VNA in the 10-1000MHz range? Any estimates of the difference in sensitivity?
My interest in the 10-1000MHz range is because I hope to measure S21 (magnitude and phase) in that frequency band at extremely low signal levels, most likely between -130dBm to -100dBm. The architecture in attached write-up can be adapted to work in this sub-GHz band.