The difference between a spray head and a rotor head is quite significant. A rotor, also called impact type head has between a 4 to 12" pop up height and rotates a preset radius with a stream of water. A spray head, also called pop-up or fan, ranges from a 2 to 12" pop up height and does just what it says, pops up and shoots a fan type stream, which comes in different radii as well. Spray heads are used for small areas, and rotors are used for large areas. Which ever the sprinkler you have is, sounds like a spray, you will want to replace it with one of the same. It doesn't have to be the same brand, just the same type, so that the precipitation rates are the same.
Tony Posey
Ridge Run Landscapes