This is a complete C-Band 300W Dummy Load and Cross Guide Coupler subsystem allowing the safe testing of any C-Band amplifier of less than 300 watts.
Admittedly the 300 watt capacity is a guess based on its size. The manufacturers label calls it a 12297 G2 and we searched the Internet but could not find a reference. All dummy loads have two values, one is the maximum continuous absorption rating and the other is a peak rating designed for short bursts of power.
The other major component in the assembly is the cross-guide coupler with an N connector and 50 dB attenuation.