Details of the HAARP Antenna Design

The complete HAARP antenna system is a technically known as a Planar Array, consisting of multiple horizontally polarized antenna elements. Each of these individual antenna elements, in turn, consists of two upper and two lower crossed dipole antennas mounted to a mast (or tower) above a wire mesh ground screen. The upper or lower crossed dipoles are selected depending on the desired operating frequency range. Because the design of these elements is mechanically complex, the drawings used in the following discussion have been simplified to include only half of the crossed dipoles making up each element. (The other dipoles would be going into or coming out of the page.)

There is one transmitter cabinet (see Transmitter Information) dedicated to each antenna mast. In the completed facility there will be 180 masts and 180 transmitter cabinets. Each transmitter cabinet contains two identical transmitters, each of which is capable of producing a maximum output power of 10 kW. Thus, the maximum power that can be delivered to any of the array elements (or masts) in the array is 20 kW.

The Complete Antenna Element

Each element making up the HAARP antenna array consists of four selectable dipole antennas (two are shown here), which are aligned very nearly north-south and east-west. The dipoles are mounted to an aluminum tower 72 feet high which is supported at its base by a thermopile for reliable and long-lasting stability. A wire mesh, ground screen is attached mechanically and electrically to the tower at a height of 15 feet above the ground.

The Low Band Dipole

The HAARP antenna is expected to operate at frequencies within a wider range than is normally possible with a simple wire or tubular dipole. As a result, it was necessary to "fatten" the dipole elements with a wire cage design. Using this approach, the impedance bandwidth of the dipoles can be increased significantly. The large diameter, horizontal aluminum tubes that are prominent in photographs of the array are actually only the tops of the low band dipole elements which will operate effectively at frequencies within the range 2.8 - 7 Mhz. The low band element is attached to the tower at a height of 38 feet above the ground screen.

The High Band Dipole

For frequencies between 7 - 10 Mhz, the high band dipoles are selected using switches contained in the balun boxes. The high band dipoles are physically simpler than the low band dipoles and are constructed entirely of aluminum wire which makes them less visible in photographs of the array. The high band dipoles are supported mechanically from the upper, large diameter aluminum tube that is part of the low band dipole, using insulated Kevlar guy ropes and are attached to the tower at a point 28 feet above the ground screen.

The Matching Networks and Balun

Antenna Matching Units ("AMU" in the figure) are used to further improve the input impedance of the dipole elements. There are two AMUs per dipole and they are mounted to the tower just above the point where the dipole itself is attached. (Photo) Each two sets of dipoles (high and low band, north-south, for example) is fed through a Balun to convert the coaxial (unbalanced) transmission line from the transmitters to the balanced input of the antenna. The complete antenna structure is supported by insulated, Kevlar guy ropes attached from the top of the tower to the aluminum tubes. Brightly colored "bird balls" ("B") are attached to these guy ropes to help birds avoid the antenna structure. A wire mesh ground screen ("GS") is positioned below the entire antenna array at a height of 15 feet above ground. It is attached to each tower through separate mechanical and electrical connections.



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Last updated July 11, 1997.