Iranian designed surface to air missile systems/air defence systems, with some local manufacturing in Yemen. This includes traditional radar based SAM systems, anti aircraft loitering munitions, and "FrankenSAMs" that involve launching infrared and active radar guided air to air missiles from the ground from makeshift launchers. Not exactly the kind of equipment available to protestors. Ukraine uses very similar equipment, aside from the anti aircraft loitering munitions which they don't have. And Ukraine has advanced high level systems like Patriot and S-300 which Yemen don't have.

Good article on this