Upper panel: measured S₁₁ for the NAOJ feedhorn design. The purple curve presents data measured directly with WR10 VNA extenders, whereas the black curve (> 110 GHz) shows data taken with WR6 extenders and waveguide transitions and are affected by the S₁₁ of the additional transitions. Lower panel: comparison of the NAOJ feedhorn beam pattern from simulations and measurements at 95 GHz, close to the central frequency of 91.5 GHz. Our EM simulations confirm that the beam properties scale smoothly as a function of wavelength, and hence we only show one representative frequency.