How to understand the EIRP criteria in 47 CFR § 15.519 for UWB device?
But I don't undersand why with 1KHz resolution bandwidth, in 1164~1240MHz, EIRP in dBm is -83.5. I would guess -75.3dBm-30dBm=-105.3dBm because 1KHz is just 1/1000 of 1MHz, and the total power in this bandwidth would be 30dB less.


You're assuming that essentially the same power density would be allowed in all allowed bands.

That's not the case. 

UWB regulation was the result of half a decade of intense lobbying. And if you'd ask me, personally, that legislation has led to commercial infeasibility of basically any relevant UWB technology, back when UWB was a hot topic.


  \$20\log(RBW/50)\$ dBm, rather than \$10\log(RBW/50)\$


I must admit I don't know.