Diplexer is the equipment that combines two signal into one and divide one signal into two.
Diplexer is used for multi-band system (which handles different frequency).
The inner structure is as follows.
![](https://ensatellite.com/wp/wp-content/uploads/diplexer.png)
The diplexer has high pass filter (HPF) and low pass filter (LPF).
The signals come from right side of the image are combined.
The opposite direction can be used.