What about masers? The atmosphere should be fairly transparent in that frequency range so no need to worry about scattering, and the wavelength is short enough so you don't have to worry too much about near field effects.
Beyond obvious military application, imagine this as an alternative to laser engravers and cutters that would need no light-absorbing enclosure and light-absorbing glasses.
1) Dust — anything in the range 1mm to 1nm, depending on what properties you want it to have. Give it a small electric charge and accelerate it conventionally, perhaps in a vacuum with a plasma window at one end.
2) A relativistic beam of something that quickly decays in a way that doesn’t emit much EM radiation. (Would muons fit this description? I don’t know, I’m relying on what Wikipedia says).
[0] https://pureadmin.qub.ac.uk/ws/portalfiles/portal/124726142/... [1] https://www.ncbi.nlm.nih.gov/pubmed/21935245 [2] https://www.sciencedirect.com/science/article/pii/S016943321...