How to preserve signal power in a splitter?
Yes, it is &quot;slightly more complex&quot;. In general, if you don't terminate all of the outputs of the power splitter with the correct impedance, then the impedance at its &quot;common&quot; port will not match the impedance of the transmission line and antenna, and some power will be reflected back toward the antenna, reducing the amount of power going into the splitter in the first place. The specific amount depends on the design of your particular device, so I can't give you a number.
So yes, with a 3-way splitter, each output gets 1/3 of the input power (or actually slightly less, depending on how efficient it is), regardless of whether you use it or not. Since unused ports are terminated, the power there is simply wasted. If you really only need 2 ports, get a 2-port splitter.