English: Diagram of one of the two identical antenna arrays at the U.S. Navy Cutler VLF transmitter facility at Cutler, Maine. It transmits operational orders one-way to submerged submarines worldwide at a frequency of 24 kHz with a power of 1.8 megawatts. This type of antenna is called a trideco or umbrella antenna, a form of capacitively top-loaded monopole antenna. It consists of an array of 13 vertical steel masts attached at the top to a system of horizontal cables like an 'umbrella". The cables are divided into 6 "panels" which radiate out from the central tower in a pattern resembling a snowflake. The central mast is 979 ft (298 meters) tall, and the entire array is 6140 ft (1.871 km or 1.16 miles) in diameter. The vertical masts actually radiate the VLF radio waves, while the top cables form a large capacitor with the ground, which serves to increase the efficiency of the antenna. Under each mast there is also a system of cables suspended a few feet above the ground radiating from the mast base, called a Counterpoise (not shown) which functions as the other plate of the capacitor.