Here are some pics of the bridge, and test results on the VNA, and then using the SH 124B + TG
I am measuring directivity by normalising with the test port open, attaching a 50 ohm load onto the test port and then making the measurement.
Edit: sorted out the pics, note that I was tweaking the tuning tab all of the time so the images show different tunings.
Bridge pics
Directivity tuned for 6GHz
Directivity tuned for best under 3GHz
Return loss
Difference between open and short
Attached images show the directivity measured on the Signalhound.