hi, @norticum
Welcome to community. 
I am looking at the datasheet of this antenna.
and… I don´t see support for LTE 5G frequencies. So… maybe you need to replace it.
All SMA connectors are used to do 4G/4G+/5G LTE. it is called diversity for best LTE coverage.
Look at this link… not same device at yours… but have a good explanation about how it work.