PTP450 Power Output

In the  Power Section of the PTP450 user configuration software, it shows the transmitter power output as 25dBm, andthen beside it there is a field that says "(22 dBm A/ 22dBm B)".  

If I change the transmitter power output to 19dBm, that field says " (16 dBm A/ 16dBm B)"; there is always a 3 dB reduction from the TPO.  

What does this mean?


This is because we're dealing with MIMO equipment, which has two chains - A and B. Combined power from two equal sources 3 dB (2 times) higher than from single source.