Latest LTE and 5G standards include diversity and multiple-input-multiple-output (MIMO) antennas. The purpose of those is to improve the reliability of connections by increase reception sensitivity and enable higher data rates.
Diversity antenna is a second reception (Rx) only antenna with different radiation characteristics than the main antenna which has transmission (Tx) capabilities as well. Both Main and Diversity antennas should be about equal in performance to get the most benefit out of the diversity
functionality which is about 3dB.
MIMO can have 2, 4, 8, or even more MIMO antennas in reception (Rx-MIMO). Usually, there is only one transmission antenna but in a certain application, multiple Tx-MIMO antennas are used. For a MIMO antenna to be useful they need to differ from each other which means the location, antenna itself, or both need to be different from one antenna to another.