How effective are different types of radar in space over large distances? Is radar significantly different outside of the atmosphere of Earth?

Would you need to generate a more powerful signal to cover multiple AU distances? Or would you need a more sensitive type of receiver?

Would passive radar be less effective? Do signals of opportunity even bounce off objects in space well enough to register in a passive radar system? There are a lot of loud objects in space that constantly generate noise, so I assume passive radar might actually be fairly accurate.