Manufacturers' recommendations for ground plane for GPS patch antennas
It depends on the antenna, and the recommendations in their datasheets. I've used some with and some without ground planes (depends on the antenna construction). To figure out the best configuration, you'd have to build a PCB with both and test signal levels to see which is better. I don't have time/resources for that so I trust the manufacturer (sometimes). You could always rip the antenna apart, figure out what type it is (or whether the antenna has a built in ground plane) inside and simulate it, I don't have time for that either.