Holmdel Horn Antenna

The horn antenna at Bell Telephone Laboratories in Holmdel, New Jersey, was constructed on Crawford Hill in 1959 to support Project Echo, the National Aeronautics and Space Administration's passive communications satellites, The antenna is in length with a radiating aperture of and is constructed of aluminum. The antenna's elevation wheel, which surrounds the midsection of the horn, is in diameter and supports the structure's weight using rollers mounted on a base frame. All axial or thrust loads are taken by a large ball bearing at the narrow apex end of the horn. The horn continues through this bearing into the equipment building or cab. The ability to locate receiver equipment at the horn apex, thus eliminating the noise contribution of a connecting line, is an important feature of the antenna. A radiometer for measuring the intensity of radiant energy is located in the cab. When not in use, the turntable azimuth sprocket drive is disengaged, allowing the structure to "weathervane" and seek a position of minimum wind resistance. The antenna was designed to withstand winds of , and the entire structure weighs 18 short tons (16 tonnes). A plastic clapboarded utility shed with two windows, a double door, and a sheet-metal roof, is located on the ground next to the antenna. This structure houses equipment and controls for the antenna and is included as a part of the designation as a National Historic Landmark. ==Technical==

This type of antenna is called a Hogg or horn-reflector antenna, invented by Alfred C. Beck and Harald T. Friis in 1941. It was built by David C. Hogg. It consists of a flaring metal horn with a curved reflecting surface mounted in its mouth at a 45° angle to the long axis of the horn. The reflector is a segment of a parabolic reflector, so the antenna is a parabolic antenna that is fed off-axis. A Hogg horn combines several characteristics useful for radio astronomy. It is extremely broad-band, has calculable aperture efficiency, and the walls of the horn shield it from radiation coming from angles outside the main beam axis. Therefore, the back and side lobes are so minimal that scarcely any thermal energy is received from the ground. Consequently, it is an ideal radio telescope for accurately measuring low levels of weak background radiation. The antenna has a gain of about 43.3 dBi and a beamwidth of about 1.5° at 2.39 GHz and an aperture efficiency of 76%. ==Preservation==

In 2021, the Crawford Hill site was sold to a developer who was interested in constructing a residential development. This triggered a petition to preserve the property as a park, which preservationists preferred over real estate development. The petition was given to township officials in March 2023, having accumulated over 6,900 signatures. That April, township officials filed a lawsuit in the New Jersey Superior Court to clarify who owned the antenna; the site developer, Crawford Hill Holdings claimed that it owned the antenna and would preserve the property. That June, the town moved to acquire the antenna. In October 2023, the township announced plans to buy and preserve the antenna. The purchase included $5.5 million for of land, which would be converted into a public park. The purchase was finalized in January 2024, when the township announced plans for the park. In May 2025, the Institute of Electrical and Electronics Engineers dedicated a plaque commemorating the antenna. ==See also==