Coaxial Waveguide Adapter, 2.4 mm (f), 26.5 to 40 GHz
R281A - Keysight Technologies
The Keysight R281A adapter transforms waveguide transmission line into 50-ohm coaxial line. Power can transmitted in either direction, and each adapter covers the full frequency range of its waveguide band with SWR less than 1.3.