Originally Posted by LarryJ
They have PRM ILS approaches at a few airports which allow approaches to closely spaced runways but not as closely spaced as the runways at SFO. MSP is one of the airports with PRM approaches and those runways are separated by the terminal complex.
Another possibility is MLS (microwave landing system). Far more accurate and flexible than ILS, and has been on trial at heathrow for a while. Widespread adoption looks uncertain though, because costs will be a lot higher than precision DGPS approaches.