Efficiency is a measure of the percentage of signal actually captured by the dish feed system. An ideal feed would capture all the signal that the dish intercepts. In the real world some signal is blocked by the feed structure and the reflective surface is never perfectly accurate. As a result, typical efficiencies range from lows of 40% for inferior products to 70% or even higher for excellent quality prime-focus antennas. Offset fed parabolic antennas can have efficiencies in excess of 80%.