Loosing Antenna , flashing screen and restarting

Hi there

I've faced a problem since. I lose my antenna signal (on both 3g & 2g or auto connect) frequently, then when antenna signal bars return, suddenly screen flashes to black and back then I lose antenna bars again. and this happens for a while till it gets restart almost every time this happens.

I see multiple wired things also; while screen flashes,
sometimes some apps would stop working like instagram, battery docter, goole & google gesture and ...
sometimes i see a notification stating my sd card is damaged and needs format! (some times sd card is empty!)
and like that...

while restarting when samsung logo or even note 8 logo comes up, I see these flashing screen continus

I guess these happens while I am at areas with not very satisfying signals, although I had this problem while I had no sim card in it too!
what is wrong guys?

Note 8 5100
android 4.4.2 official ROM
(I thought of it as a software problem and upgraded to kit kat but no chance!)

Problems with 2G/3G Signal Reception. Antenna issues?

Folks.

I dropped my phone once and since then, it has very bad connectivity. Flashed all sorts of ROMs and radios but nothing would work. I am afraid this is a physical damage/dislocation to either antenna or the 2G/3G GSM Radio Chip, since 4G/LTE works mostly fine.

Any idea what might have gone wrong?