from study, i suspect fringing capacitance effect on open transmission line or calibration kit will have effect on the accuracy of the KC901 VNA series measurement (including the latest KC901V). either the VNA designer has put default values for it or no at all in the calculation model, i dont know. but different open calibration standard kit will have different fringing capacitance effect, this will effect s-parm correction matrix if not input the right values, hence giving wrong measurement. i suggest KC901V designer will open up calibration kit data for user to enter in firmware, similar to brand name VNA like Keysight and Anritsu VNA. because i need to get 3rd party SMA Calibration Kit to move reference plane further away from KC901V for convenience measurement, most good cal kit will provide the data and parameters, but i cannot see it inputable in KC901V firmware, except just offset length. now, i cannot guarantee the KC901V will give me the right measurement, maybe just estimate.
hi mjohnellis, i think i agree with you, we should be able to get some ballpark from it, furthermore i bought a cal kit from Kirkby Microwave. the fringing capacitance effect for the Open standard is too small to worry about i guess. if i tune the offset length to the mean value (which is near center operating freq of KC901V ie at 3.5GHz), i will have max deviation of 0.162 mm (0.54 ps), my uneducated guess, this should give little impact to the accuracy. but still, its better to have a device that accepts variable delays for each frequency, like commercial one. i'm guessing this only need to be done in firmware (no hardware modification needed) and the KC901V's designer only need to find a proper book to read further on this matter (mathematical formulation).
I like your question, but is it possible this VNA is not accurate enough to worry about the fringing effect? I have used it for awhile and it gets me in the ballpark, but it is not going to compete with high end VNA's. Just the cal kit alone costs more than this VNA, but again, good question. I hope someone with more knowledge than me answers it properly.