The most familiar dish is the prime-focus parabola which has a feed/LNB mounted at its focal point, typically secured by three or four supporting arms or a buttonhook assembly. A perfect dish would detect nothing but satellite signals. However, this goal is never achieved since its surface is never perfectly accurate and even a perfect dish would "see" signals coming from off-boresight directions. In addition, the feed and LNB that are located in front of the dish inevitably block some of the incoming signal.