Cellular Antenna Issues Galaxy Note 9

I dropped my Samsung Galaxy Note 9 last October, cracking the screen and display assembly. I replaced the display assembly myself (and replaced the charging port), but ever since have been getting a weaker than normal cell signal. It is typically one or two bars less than my brothers device at any given location. This issue leads to dropped/ unstable calls, failure to send texts, etc. GPS antenna also seams to go offline more frequently. I’ve tried all the software fixes, and am convinced it is hardware related. Where are the antenna locations on the phone? Are they replaceable or modifiable?