Suggestions for toggling between 3 voltage levels from 100MHz to 1 GHz, to generate square waves?
You could attempt to build it with a pair of fast VCSEL laser drivers such as the ONET8501V. I'm not sure this would give you the output ranges that you are looking for, but it should be good in term of speed.







simulate this circuit &ndash; Schematic created using CircuitLab

If you end up building such circuit, please share your results, I am very curious about the performances you would get.

Edit: You may need some heavy RF engineering to combine the output of U2 and U3 over a wide frequency band.