I'm trying to characterize a waveguide directional coupler with a coaxial coupled port using an N5224A with a R11664A cal kit. I chose the Smartcal, performed a 2 port cal, and measured S21 and S11 on the thru leg of the coupler. But I'm stuck as to how to measure the coupled port. How do I calibrate the PNA for a mixed waveguide-coaxial measurement? Any guidance would be appreciated. Thanks.