very interesting here as part of the article to talk about diamond usage as heatsink for various applications and Huawei's interest and patents in it.
5G base station power amplifier is a pretty good proxy of the upper limit of what current material can withstand.
It says here that power amplifier density of single MMIC can reach 300 W/cm2.
if we put that inside the nose of a fighter jet.
Something with a 100 cm diameter nose (1m nose is basically flanker), that is 50*50*3.14 = 7850 cm2.
Even with that, the theoretical limit of the radar for power could be 2.355MW. Of course in reality, you might not want each MMIC to be side to side with each other, so it's going to be less than that.
But if we use something ike J-36 nose of 200cm diameter, you'd 4x that. So, that would be 8MW. Not that I think a fighter jet would actually be able to do that anytime soon, but with diamond substrate, the sky is the limit when it comes to radar power. At minimum, the constraint is not on the MMIC itself but rather whatever is providing the power & whatever is doing the cooling.