LNA output noise floor at receiver front end.

Hi,

i am designing a broadband (100 MHz -6 GHz BW) receiver chain for  radar/rcs measurement tester. i will put Low noise amplifier after antenna input followed by mixed(10 MHz IF BW and digitizer.

I am facing problem regarding LAN. bandwidth of LAN is  approx 6 GHz(100 MHz-6GHz), gain 25-35 dB, with NF less than 2. I am uncertain about noise floor at the output of LNA.  I dont know exact SNR at the input of LNA but it shall be good.System operation will be on stepped CW waveform so receiver input signal will sweep over the BW and some step size.

so LNA output r noise floor will be? i assume, we can neglect thr role of input noise because it will be lesser than internal noise of LNA.

will it be LNA internal noise (Thermal noise due to BW) only ?

will it be LNA internal noise (Thermal noise due to BW)  + LAN Gain ? -78+25 =-53 dB? internal noise shall be lesser because NF is less than 3 . 

i have practically observed that that output noise floor is much lesser then even thermal noise( over LNA BW). i have gone through some tutorial where  formula says( internal noise+input noise)+gain. in  my case input noise shall be much less than theoretical internal noise. 

Thanks