I used a single-conversion architecture, meaning RF signals from the directional couplers are downconverted to an IF frequency and then digitized. On the left side of the main PCB you can see the 3 receivers (mixer, filter, baseband amplifier, and ADC).
After the signal is digitized, its phase and amplitude is calculated and averaged on the FPGA. the values are sent to the computer via USB, where the software I wrote displays a smith chart and S11/S21 graphs.
More info and design files on github: