Difference between RF splitter and coupler?
A splitter definitely won't work. It's a device that accepts an input signal and delivers multiple output signals.

I think that you need a directional coupler. It has an input, an output, a coupled port, and a load. It's a device that operates on an input so that two output signals are available, on the output port (larger signal) and the coupled port (smaller signal). However, when the input is applied to the opposite port of a terminated coupler, only one output signal is produced. MCL makes suitable devices.