You not search this forum.
You not read a vendor documentation like: https://mikrotik.com/product/r11e_lte6#fndtn-downloads > Brochure.
From B3/1/7 only B3+B7 can be 2xCA as INTER..
B3+B3 or B1+B1 or +B7+B7 as INTRA
Every B3/1/7 can be 2CA with B8/20
Read documentation or search this forum http://forum.mikrotik.com/t/sxt-lte-4g-cat6/134468/1 .