What sort of regulations are you trying to comply with? Who's? What sort of product?
That should tell you bandwidth, though as I understand it, most of them don't get into the GHz range unless you're transmitting or you're operating at higher frequencies.... there are a lot of nuances of the laws in different places and for different classes of devices and while a few do require a lot of bandwidth, but most basic stuff will only get to a few hundred MHz.