The Cassegrain or "back-fire" dish also has a parabolic surface but then redirects the incoming satellite signals via a second reflector, the hyperbolic subreflector, down a waveguide to an LNB mounted in a rear position. This type, often more expensive than more common prime-focus dishes, is usually installed in commercial earth stations. The Cassegrain geometry can be very useful in hot climates because the LNB is mounted behind the reflective surface where it is protected from the direct rays of the sun, remains relatively cool and functions more efficiently.