A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz. They are used as feed antennas (called feed horns ) for larger antenna structures such as parabolic antennas , as standard calibration antennas to measure the gain of other antennas, and as directive antennas for such devices as radar guns , automatic door openers , and microwave radiometers . Their advantages are moderate directivity , broad bandwidth , low losses, and simple construction and adjustment.
37-661: The Holmdel Horn Antenna is a large microwave horn antenna that was used as a satellite communication antenna and radio telescope during the 1960s at the Bell Telephone Laboratories facility located on Crawford Hill in Holmdel Township, New Jersey , United States. It was designated a National Historic Landmark in 1989 because of its association with the research work of two radio astronomers , Arno Penzias and Robert Wilson . In 1965, while using this antenna, Penzias and Wilson discovered
74-508: A gain of about 43.3 dBi and a beamwidth of about 1.5° at 2.39 GHz and an aperture efficiency of 76%. In 2021, the Crawford Hill site was sold to a developer who was interested in building a residential development. In reaction, this triggered a "Save Holmdel's Horn Antenna" petition to preserve the property as a park. Advocates felt that a better fate than the horn antenna or its site encountering destruction to make way for
111-403: A center pintle ball bearing on a turntable track 30 feet (9.1 m) in diameter. The track consists of stress-relieved, planed steel plates individually adjusted to produce a track that is flat to about 1 ⁄ 64 inch (0.40 mm). The faces of the wheels are cone-shaped to minimize contact friction. A tangential force of 100 pounds (400 N) is sufficient to start the antenna rotating on
148-427: A feed horn for microwave antennas such as satellite dishes and radio telescopes . An advantage of horn antennas is that since they have no resonant elements, they can operate over a wide range of frequencies , a wide bandwidth . The usable bandwidth of horn antennas is typically of the order of 10:1, and can be up to 20:1 (for example allowing it to operate from 1 GHz to 20 GHz). The input impedance
185-420: A horn as spherical wavefronts, with their origin at the apex of the horn, a point called the phase center . The pattern of electric and magnetic fields at the aperture plane at the mouth of the horn, which determines the radiation pattern , is a scaled-up reproduction of the fields in the waveguide. Because the wavefronts are spherical, the phase increases smoothly from the edges of the aperture plane to
222-503: A planned real estate development. As of October 2023, the site is now planned to be preserved. After public support for the preservation of the horn antenna emerged—demonstrated in part by more than 8,000 signatures on a petition disseminated by community groups—the Holmdel Township Committee agreed to pay $ 5.5 million for 35 acres (14 ha) of land, including that which the antenna sits on. The town plans to turn
259-489: A pyramidal horn, the dimensions that give an optimum horn are: For a conical horn, the dimensions that give an optimum horn are: where An optimum horn does not yield maximum gain for a given aperture size . That is achieved with a very long horn (an aperture limited horn). The optimum horn yields maximum gain for a given horn length . Tables showing dimensions for optimum horns for various frequencies are given in microwave handbooks. Horns have very little loss, so
296-401: A short length of rectangular or cylindrical metal tube (the waveguide), closed at one end, flaring into an open-ended conical or pyramidal shaped horn on the other end. The radio waves are usually introduced into the waveguide by a coaxial cable attached to the side, with the central conductor projecting into the waveguide to form a quarter-wave monopole antenna. The waves then radiate out
333-417: A standard parabolic antenna is that the horn shields the antenna from radiation coming from angles outside the main beam axis, so its radiation pattern has very small sidelobes . Also, the aperture isn't partially obstructed by the feed and its supports, as with ordinary front-fed parabolic dishes, allowing it to achieve aperture efficiencies of 70% as opposed to 55–60% for front-fed dishes. The disadvantage
370-547: A tapered transmission line , or an optical medium with a smoothly varying refractive index. In addition, the wide aperture of the horn projects the waves in a narrow beam. The horn shape that gives minimum reflected power is an exponential taper. Exponential horns are used in special applications that require minimum signal loss, such as satellite antennas and radio telescopes . However conical and pyramidal horns are most widely used, because they have straight sides and are easier to design and fabricate. The waves travel down
407-460: 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
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#1732782561698444-403: 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
481-406: Is often used. The aperture efficiency increases with the length of the horn, and for aperture-limited horns is approximately unity. A type of antenna that combines a horn with a parabolic reflector is known as a Hogg-horn, or horn-reflector antenna, invented by Alfred C. Beck and Harald T. Friis in 1941 and further developed by David C. Hogg at Bell Labs in 1961. It is also referred to as
518-408: Is slowly varying over this wide frequency range, allowing low voltage standing wave ratio (VSWR) over the bandwidth. The gain of horn antennas ranges up to 25 dBi , with 10–20 dBi being typical. A horn antenna is used to transmit radio waves from a waveguide (a metal pipe used to carry radio waves) out into space, or collect radio waves into a waveguide for reception. It typically consists of
555-408: Is some flare angle that gives minimum reflection and maximum gain. The internal reflections in straight-sided horns come from the two locations along the wave path where the impedance changes abruptly; the mouth or aperture of the horn, and the throat where the sides begin to flare out. The amount of reflection at these two sites varies with the flare angle of the horn (the angle the sides make with
592-454: Is that it is far larger and heavier for a given aperture area than a parabolic dish, and must be mounted on a cumbersome turntable to be fully steerable. This design was used for a few radio telescopes and communication satellite ground antennas during the 1960s. Its largest use, however, was as fixed antennas for microwave relay links in the AT&;T Long Lines microwave network. Since
629-463: The cosmic microwave background radiation (CMBR) that permeates the universe. This was one of the most important discoveries in physical cosmology since Edwin Hubble demonstrated in the 1920s that the universe was expanding. It provided the evidence that confirmed George Gamow 's and Georges Lemaître 's " Big Bang " theory of the creation of the universe. This helped change the science of cosmology,
666-499: The directivity of a horn is roughly equal to its gain . The gain G of a pyramidal horn antenna (the ratio of the radiated power intensity along its beam axis to the intensity of an isotropic antenna with the same input power) is: For conical horns, the gain is: where The aperture efficiency ranges from 0.4 to 0.8 in practical horn antennas. For optimum pyramidal horns, e A = 0.511., while for optimum conical horns e A = 0.522. So an approximate figure of 0.5
703-429: The "sugar scoop" due to its characteristic shape. It consists of a horn antenna with a reflector mounted in the mouth of the horn at a 45 degree angle so the radiated beam is at right angles to the horn axis. The reflector is a segment of a parabolic reflector, and the focus of the reflector is at the apex of the horn, so the device is equivalent to a parabolic antenna fed off-axis. The advantage of this design over
740-501: The 1970s this design has been superseded by shrouded parabolic dish antennas , which can achieve equally good sidelobe performance with a lighter more compact construction. Probably the most photographed and well-known example is the 15-meter-long (50-foot) Holmdel Horn Antenna at Bell Labs in Holmdel, New Jersey, with which Arno Penzias and Robert Wilson discovered cosmic microwave background radiation in 1965, for which they won
777-470: The Earth to another. The antenna is 50 feet (15 m) in length with a radiating aperture of 20 by 20 feet (6.1 by 6.1 m) and is constructed of aluminum . The antenna's elevation wheel, which surrounds the midsection of the horn, is 30 feet (9.1 m) 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
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#1732782561698814-411: The axis). In narrow horns with small flare angles most of the reflection occurs at the mouth of the horn. The gain of the antenna is low because the small mouth approximates an open-ended waveguide, with a large impedance step. As the angle is increased, the reflection at the mouth decreases rapidly and the antenna's gain increases. In contrast, in wide horns with flare angles approaching 90° most of
851-406: The center, because of the difference in length of the center point and the edge points from the apex point. The difference in phase between the center point and the edges is called the phase error . This phase error, which increases with the flare angle, reduces the gain and increases the beamwidth, giving horns wider beamwidths than similar-sized plane-wave antennas such as parabolic dishes. At
888-408: The conductive walls causes an abrupt impedance change at the aperture, from the wave impedance in the waveguide to the impedance of free space , (about 377 Ω ). When radio waves travelling through the waveguide hit the opening, this impedance-step reflects a significant fraction of the wave energy back down the guide toward the source, so that not all of the power is radiated. This is similar to
925-422: The design. Assistance in the design was also given by Messrs. R. O'Regan and S. A. Darby. Construction of the antenna was completed under the direction of Arthur Crawford. 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 100 miles per hour (160 km/h), and
962-449: The entire structure weighs 18 short tons (16 tonnes). A plastic clapboarded utility shed 10 by 20 feet (3.0 by 6.1 m) 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. The antenna has not been used for several decades. This type of antenna
999-509: The flare angle, the radiation of the beam lobe is down about 20 dB from its maximum value. As the size of a horn (expressed in wavelengths) is increased, the phase error increases, giving the horn a wider radiation pattern. Keeping the beamwidth narrow requires a longer horn (smaller flare angle) to keep the phase error constant. The increasing phase error limits the aperture size of practical horns to about 15 wavelengths; larger apertures would require impractically long horns. This limits
1036-460: The gain of practical horns to about 1000 (30 dBi) and the corresponding minimum beamwidth to about 5–10°. Below are the main types of horn antennas. Horns can have different flare angles as well as different expansion curves (elliptic, hyperbolic, etc.) in the E-field and H-field directions, making possible a wide variety of different beam profiles. For a given frequency and horn length, there
1073-415: The horn end in a narrow beam. In some equipment the radio waves are conducted between the transmitter or receiver and the antenna by a waveguide; in this case the horn is attached to the end of the waveguide. In outdoor horns, such as the feed horns of satellite dishes, the open mouth of the horn is often covered by a plastic sheet transparent to radio waves, to exclude moisture. A horn antenna serves
1110-644: The land into a public park. [REDACTED] Media related to Holmdel Horn Antenna at Wikimedia Commons Horn antenna One of the first horn antennas was constructed in 1897 by Bengali-Indian radio researcher Jagadish Chandra Bose in his pioneering experiments with microwaves. The modern horn antenna was invented independently in 1938 by Wilmer Barrow and G. C. Southworth The development of radar in World War II stimulated horn research to design feed horns for radar antennas. The corrugated horn invented by Kay in 1962 has become widely used as
1147-456: 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. The triangular base frame of the antenna is made from structural steel. It rotates on wheels about
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1184-460: The reflection at an open-ended transmission line or a boundary between optical mediums with a low and high index of refraction , like at a glass surface. The reflected waves cause standing waves in the waveguide, increasing the SWR , wasting energy and possibly overheating the transmitter. In addition, the small aperture of the waveguide (less than one wavelength) causes significant diffraction of
1221-454: The reflection is at the throat. The horn's gain is again low because the throat approximates an open-ended waveguide. As the angle is decreased, the amount of reflection at this site drops, and the horn's gain again increases. This discussion shows that there is some flare angle between 0° and 90° which gives maximum gain and minimum reflection. This is called the optimum horn . Most practical horn antennas are designed as optimum horns. In
1258-413: The same function for electromagnetic waves that an acoustical horn does for sound waves in a musical instrument such as a trumpet . It provides a gradual transition structure to match the impedance of a tube to the impedance of free space, enabling the waves from the tube to radiate efficiently into space. If a simple open-ended waveguide is used as an antenna, without the horn, the sudden end of
1295-703: The study of the universe's history, from a field for unlimited theoretical speculation into a discipline of direct observation. In 1978 Penzias and Wilson received the Nobel Prize for Physics for their discovery. 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, which used large aluminized plastic balloons ( satellite balloon ) as reflectors to bounce radio signals from one point on
1332-475: The turntable. The antenna beam can be directed to any part of the sky using the turntable for azimuth adjustments and the elevation wheel to change the elevation angle or altitude above the horizon. Except for the steel base frame, which a local steel company made, the Holmdel Laboratory shops fabricated and assembled the antenna under the direction of Mr. H. W. Anderson, who also collaborated on
1369-464: The waves issuing from it, resulting in a wide radiation pattern without much directivity. To improve these poor characteristics, the ends of the waveguide are flared out to form a horn. The taper of the horn changes the impedance gradually along the horn's length. This acts like an impedance matching transformer , allowing most of the wave energy to radiate out the end of the horn into space, with minimal reflection. The taper functions similarly to
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