English: Marine radar antenna on the stern of a small boat. This type of radar usually operates on S-band, 2 to 4 GHz. This type of antenna is called a slot antenna, consisting of a waveguide with many narrow slots cut in it. It radiates a narrow fan-shaped radar beam, perhaps 15° high and 2-3° wide, in a horizontal direction, so that even if the boat is pitching in high seas and the antenna is tilted at an angle, part of the beam will still be pointed toward the horizon, where the targets are. The antenna is rotated about its vertical axis by a motor in the white housing below the antenna at a rate of about a revolution every 2 seconds to scan the entire horizon, searching for other ships.