Hi Experts.
n 5G, there are multiple types of beams that are used to transmit different types of information. For instance, we have broadcast beams and traffic beams.
The Broadcast beams are mainly the common channel beams that are used to transmit SSB. The same beams are also used for other broadcast channels like CSI resources.
Then we have traffic beams which are mostly based on PMI or SRS. If the PMI based beams are used then those beams depend on CSI resources and configuration as the UE decodes the CSI resources to generate CSI feedback which carries the PMIs. If the SRS based beams are used then those depend on the UE’s uplink coverage and the gNB uses the SRS to estimate the optimal beam candidate for the UE.
In a nutshell,
- SSB Beams are Broadcast Type beams and cover larger areas.
- PMI based Beams are more focused and narrower. They are Traffic Type Beams.
- SRS Based Beams can be even more focused and they are also Traffic Type Beams.
Watch on YouTube: 
https://www.youtube.com/watch?v=J-1X8C6unms