By scalar wave you mean an oscillation of a scalar field? Almost all mechanical waves are "scalar": a sound wave, for example, is a fluctuation of air pressure and density, which are both scalar fields

TANSTAAFL

I've done some research on em scalar waves. I've found a lot of free energy stuff that doesn't really offer any insight into the problem because they offered no math in support of their argument, so I'm not going to give credit to them. However I managed to dig up a declassified document from the CIA on scalar waves which actually offers a little bit of math that I think I can use to see if scalar waves are actually predicted by the Maxwell equations.

I'll write again when if I find anything useful.