A Coupler reduces (attenuates/diminishes) the incoming or amplified signal, especially where multiple indoor antennas are used (DAS). As with an attenuator, it will attenuate closer antennas to the booster by a measured amount so that all indoor antennas will produce the same coverage/output (the same indoor signal strength throughout) the installation.

But unlike an attenuator, the couple has a straight-through unattenuated line, but the arm is attenuated. This eliminates the use of splitters and reduces costs.