Amateur radio, also known as ham radio, is the use of the radio spectrum for non-commercial communication, technical experimentation, self-training, recreation, radiosport, contesting, and emergency communications. In 1927 a radio amateur was defined as "a duly authorized person interested in radioelectric practice with a purely personal aim and without pecuniary interest," meaning without monetary or similar reward. The definition distinguished amateur activity from commercial broadcasting, public safety services, and professional two-way radio uses such as maritime, aviation, and taxi communication. (Read more...)
An amateur radio operator is someone who uses equipment at an amateur radio station to engage in two-way personal communications with other amateur operators on radio frequenciesassigned to the amateur radio service. Amateur radio operators have been granted an amateur radio license by a governmental regulatory authority after passing an examination on applicable regulations, electronics, radio theory, and radio operation. As a component of their license, amateur radio operators are assigned a call sign that they use to identify themselves during communication. About three million amateur radio operators are currently active worldwide. (Read more...)
Radio waves (black) reflecting off the ionosphere (red) during skywave propagation. Line altitude in this image is significantly exaggerated and not to scale.
The Hungarian World Bus & DX-Pedition or Globexpedition (in Hungarian: Globexpedíció), also known by the radio call signHA5BUS and its variations, was a DX-pedition with the aim of traveling around the globe with a bus. The expedition lasted 614 days from 23 October 1991 to 27 June 1993, and its team traveled through or visited places in Hungary, the Soviet Union (which was in the process of dissolution at the time), Turkey, Iran, Pakistan, India, Bangladesh, Bhutan, Singapore, Australia, the United States, Canada, Germany and Austria. The participants were three Hungarian men, all licensed amateur radio (or "ham") operators; bus driver Gábor Kovács (nicknamed "Gabi", call sign: HG5BKG), Volánbusz mechanical engineer István Himberger ("Pista", HG5CHI) and Rádiózás magazine's then chief editor Imre Páskuly ("Imi", HA5HO). (Full article...)
Amateur radio station with transceivers, amplifiers, and a computer for digital modes. On the wall are awards, certificates, and QSL cards from foreign stations Amateur radio, also known as Ham radio, is the use of specific bands and frequencies within the radio spectrum for non-commercial communication, technical experimentation, self-training, recreation, radiosport, contesting, and emergency communications. A surge of popular interest in radio experimentation in the early 20th century necessitated that parts of the radio spectrum be allocated to non-professionals. In 1927 a radio amateur was defined as "a duly authorized person interested in radioelectric practice with a purely personal aim and without pecuniary interest", meaning without monetary or similar reward. The definition distinguished amateur activity from commercial broadcasting, public safety services, and professional two-way radio uses such as maritime, aviation, and taxi communication. (Full article...)
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A diving grebe creating surface waves In physics, a surface wave is a mechanical wave that propagates along the interface between differing media. A common example is gravity waves along the surface of liquids, such as ocean waves. Gravity waves can also occur within liquids, at the interface between two fluids with different densities. Elastic surface waves can travel along the surface of solids, such as Rayleigh or Love waves. Electromagnetic waves can also propagate as "surface waves" in that they can be guided along with a refractive indexgradient or along an interface between two media having different dielectric constants. In radiotransmission, a ground wave is a guided wave that propagates close to the surface of the Earth. (Full article...)
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Charles Emory Apgar (June 28, 1865 – August 17, 1950) was an American business executive and amateur radio operator. He is known for making early recordings of radio transmissions at the start of World War I. The recordings that he made of a wireless telegraphy station owned by a German Empire-based company operating from the United States were used to expose an espionage ring. They provided evidence of clandestine messages being sent in violation of a prohibition intended to maintain United States neutrality. This proof of illicit operation led to the government seizing control of the facility to stop the activity. Apgar's efforts received extensive coverage in newspapers and technical science magazines at the time. His contributions were praised by government investigators. Publications continued to remark on his work many years later. (Full article...)
U.S. Military Telegraph battery wagon, Army of the Potomac headquarters, Petersburg, Virginia, June 1864.
The U.S. Military Telegraph Corps was formed in 1861 following the outbreak of the American Civil War. David Strouse, Samuel M. Brown, Richard O'Brian and David H. Bates, all from the Pennsylvania Railroad Company, were sent to Washington, D.C. to serve in the newly created office. In October of that year, Anson Stager was appointed department head. During the war, they were charged with maintaining communications between the federal government in Washington and the commanding officers of the far-flung units of the Union Army. (Full article...)
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Antennas for High-speed Amateur-radio Multimedia Network (HamNET) in Europe, part of the AMPRNet wireless mesh network
Fixed station of a German amateur radio operator An amateur radio station is a radio station designed to provide radiocommunications in the amateur radio service for an amateur radio operator. Radio amateurs build and operate several types of amateur radio stations, including fixed ground stations, mobile stations, space stations, and temporary field stations. A slang term often used for an amateur station's location is the shack, named after the small enclosures added to the upperworks of naval ships to hold early radio equipment and batteries. (Full article...)
The Military Auxiliary Radio System (MARS) is a United States Department of War sponsored program, established as a separately managed and operated program by the United States Army and the United States Air Force. The United States Navy-Marine Corps program closed in 2015. The program is a civilian auxiliary consisting primarily of licensed amateur radio operators who are interested in assisting the military with communications on a regional and national level when access to traditional forms of communication may no longer be available. The MARS programs also include active duty, reserve, and National Guard units; and Navy, Marine Corps units. (Full article...)
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FCC amateur radio station license of Al Gross In the United States, amateur radio licensing is governed by the Federal Communications Commission (FCC). Licenses to operate amateur stations for personal use are granted to individuals of any age once they demonstrate an understanding of both pertinent FCC regulations and knowledge of radio station operation and safety considerations. There is no minimum age for licensing; applicants as young as five years old have passed examinations and were granted licenses. (Full article...)
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Heathkit is the brand name of kits and other electronic products produced and marketed by the Heath Company. The products over the decades have included electronic test equipment, high fidelityhome audio equipment, television receivers, amateur radio equipment, robots, electronic ignition conversion modules for early model cars with point style ignitions, and the influential Heath H-8, H-89, and H-11 hobbyist computers, which were sold in kit form for assembly by the purchaser. (Full article...)
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Amateur radio operator's "Radio shack" with vintage gear Vintage amateur radio is a subset of amateur radio hobby where enthusiasts collect, restore, preserve, build, and operate amateur radio equipment from bygone years, such as those using vacuum tube technology. Popular modes of operation include speaking over amplitude modulation (AM), and communicating using Morse code through continuous wave (CW) radiotelegraphy. Some enthusiasts have interest in owning, restoring and operating vintage military and commercial radio equipment such as those from 1940s to 1960s. Some undertake to construct their own gear, known in ham slang as homebrewing, using vintage parts and designs. A number of amateur radio clubs and organizations sponsor contests, events, and swap meets that cater to this specialized aspect of the hobby. (Full article...)
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Radioteletype tuning indicator Radioteletype (RTTY) is a telecommunications system consisting originally of two or more electromechanicalteleprinters in different locations connected by radio rather than a wired link. Radioteletype evolved from earlier landline teleprinter operations that began in the mid-1800s. The US Navy Department successfully tested printing telegraphy between an airplane and ground radio station in 1922. Later that year, the Radio Corporation of America (RCA) successfully tested printing telegraphy via their Chatham, Massachusetts, radio station to the RMS Majestic. Commercial RTTY systems were in active service between San Francisco and Honolulu as early as April 1932 and between San Francisco and New York City by 1934. The US military used radioteletype in the 1930s and expanded this usage during World War II. From the 1980s, teleprinters were replaced by personal computers (PCs) running software to emulate teleprinters. (Full article...)
Amateur radio or ham radio is practised by more than 22,000 licensed users in India. The first amateur radio operator was licensed in 1921, and by the mid-1930s, there were around 20 amateur radio operators in India. Amateur radio operators played an important part in the Indian independence movement with the establishment of illegal pro-independence radio stations in the 1940s. The three decades after India's independence saw only slow growth in the number of operators until the then Prime Minister of India and amateur radio operator, Rajiv Gandhi (VU2RG), waived the import duty on wireless equipment in 1984. Since then, numbers have picked up, and as of 2007[update], there were more than 16,000 operators in the country. Amateur radio operators have played a vital role during disasters and national emergencies such as earthquakes, tsunamis, cyclones, floods, and bomb blasts, by providing voluntary emergency communications in the affected areas. (Full article...)
UHF half-wave dipole In radio and telecommunications, a dipole antenna or doublet is one of the two simplest and most widely used types of antenna; the other is the monopole.[full citation needed] The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole with a radiating structure supporting a line current so energized that the current has only one node at each far end. A dipole antenna commonly consists of two identical conductive elements such as metal wires or rods. The driving current from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the two halves of the antenna. Each side of the feedline to the transmitter or receiver is connected to one of the conductors. This contrasts with a monopole antenna, which consists of a single rod or conductor with one side of the feedline connected to it, and the other side connected to some type of ground. A common example of a dipole is the rabbit earstelevision antenna found on broadcast television sets. All dipoles are electrically equivalent to two monopoles mounted end-to-end and fed with opposite phases, with the ground plane between them made virtual by the opposing monopole. (Full article...)
General images
The following are images from various amateur radio-related articles on Wikipedia.
A Beverage antenna consists of a horizontal wire from one-half to several wavelengths long (tens to hundreds of meters / yards for shortwaves; up to several kilometres / miles for longwaves) suspended above the ground, with the feedline to the receiver attached to one end, and the other end of the wire terminated through a resistor to ground. The antenna has a unidirectional radiation pattern with the main lobe of the pattern at a shallow angle into the sky off the resistor-terminated end, making it ideal for reception of long distance skywave (skip) transmissions from stations over the horizon which reflect off the ionosphere. However the antenna must be built so the wire points in the direction of the transmitter(s) to be received.
The advantages of Beverage antennas are their excellent directivity, wider bandwidth than conventional resonant antennas, and the ability to clearly receive distant and overseas transmitters. Their disadvantages are very long physical size, requiring considerable land area, and because of the length, being unfeasible to rotate to different reception directions. As a work-around, antenna installations often use multiple Beverage antennas to provide wide azimuth coverage. (Full article...)
A mast radiator (or radiating tower) is a radio mast or tower in which the metal structure itself is energized and functions as an antenna. This design, first used widely in the 1930s, is commonly used for transmitting antennas operating at low frequencies, in the LF and MF bands, in particular those used for AM radio broadcasting stations. The conductive steel mast is electrically connected to the transmitter. Its base is usually mounted on a nonconductive support to insulate it from the ground. A mast radiator is a form of monopole antenna. (Full article...)
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Typical GSM sector antenna outdoor unit A sector antenna is a type of directionalmicrowaveantenna with a sector-shaped radiation pattern. The word "sector" is used in the geometric sense; some portion of the circumference of a circle measured in degrees of arc. 60°, 90° and 120° designs are typical, often with a few degrees 'extra' to ensure overlap and mounted in multiples when wider or full-circle coverage is required (see photos below). The largest use of these antennas is as antennas for cell phonebase-station sites. They are also used for other types of mobile communications, for example in Wi-Fi networks. They are used for limited-range distances of around 4 to 5km. (Full article...)
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Pyramidal microwave horn antenna, with a bandwidth of 0.8 to 18 GHz. A coaxial cable feedline attaches to the connector visible at top. This type is called a ridged horn; the curving fins visible inside the mouth of the horn increase the antenna's bandwidth.
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 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 1GHz to 20GHz). The input impedance 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. (Full article...)
A microstrip antenna array for a satellite television receiver In telecommunication, a microstrip antenna (also known as a printed antenna) usually is an antenna fabricated using photolithographic techniques on a printed circuit board (PCB). It is a kind of internal antenna. They are mostly used at microwavefrequencies. An individual microstrip antenna consists of a patch of metal foil of various shapes (a patch antenna) on the surface of a PCB, with a metal foil ground plane on the other side of the board. Most microstrip antennas consist of multiple patches in a two-dimensional array. The antenna is usually connected to the transmitter or receiver through foil microstriptransmission lines. The radio-frequency current is applied (or in receiving antennas the received signal is produced) between the antenna and ground plane. Microstrip antennas have become very popular in recent decades due to their thin planar profile which can be incorporated into the surfaces of consumer products, aircraft and missiles; their ease of fabrication using printed circuit techniques; the ease of integrating the antenna on the same board with the rest of the circuit, and the possibility of adding active devices such as microwave integrated circuits to the antenna itself to make active antennas Patch antenna. Based on its origin, microstrip consists of two words, namely micro (very thin/small) and is defined as a type of antenna that has a blade/piece shape and is very thin/small.
The most common type of microstrip antenna is commonly known as patch antenna. Antennas using patches as constitutive elements in an array are also possible. A patch antenna is a narrowband, wide-beam antenna fabricated by etching the antenna element pattern in metal trace bonded to an insulating dielectric substrate, such as a printed circuit board, with a continuous metal layer bonded to the opposite side of the substrate which forms a ground plane. Common microstrip antenna shapes are square, rectangular, circular and elliptical, but any continuous shape is possible. Some patch antennas do not use a dielectric substrate and instead are made of a metal patch mounted above a ground plane using dielectric spacers; the resulting structure is less rugged but has a wider bandwidth. Because such antennas have a very low profile, are mechanically rugged and can be shaped to conform to the curving skin of a vehicle, they are often mounted on the exterior of aircraft and spacecraft, or are incorporated into mobile radio communications devices. (Full article...)
A cantenna (a portmanteau blending the words can and antenna) is a homemade directional waveguideantenna, made out of an open-ended metal can.
Cantennas are typically used to increase the range (or discovery) of Wi-Fi networks. (Full article...)
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Log-periodic antenna, 400–4000 MHz
A log-periodic antenna (LP), also known as a log-periodic array or log-periodic aerial, is a multi-element, directional antenna designed to operate over a wide band of frequencies. It was invented by John Dunlavy in 1952.
The most common form of log-periodic antenna is the log-periodic dipole array or LPDA, The LPDA consists of a number of half-wave dipoledriven elements of gradually increasing length, each consisting of a pair of metal rods. The dipoles are mounted close together in a line, connected in parallel to the feedline with alternating phase. Electrically, it simulates a series of two- or three-element Yagi–Uda antennas connected together, each set tuned to a different frequency.
LPDA antennas look somewhat similar to Yagi antennas, in that they both consist of dipole rod elements mounted in a line along a support boom, but they work in very different ways. Adding elements to a Yagi increases its directionality, or gain, while adding elements to an LPDA increases its frequency response, or bandwidth.
One large application for LPDAs is in rooftop terrestrial television antennas, since they may require large bandwidth to cover various frequencies in the VHF and/or UHF bands. One widely used design for television reception combined a Yagi for UHF reception in front of a larger LPDA for VHF. (Full article...)
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Adcock radio range ground station. Hundreds of these stations were deployed around the U.S. alone. The Adcock antenna is an antenna array consisting of four equidistant vertical elements which can be used to transmit or receive directional radio waves.
The Adcock array was invented and patented by British engineer Frank Adcock and since his August1919 BritishPatent No.130,490, the 'Adcock Aerial' has been used for a variety of applications, both civilian and military. Although originally conceived for receiving low frequency (LF) waves, it has also been used for transmitting, and has since been adapted for use at much higher frequencies, up to ultra high frequency (UHF).
In the early 1930s, the Adcock antenna (transmitting in the LF/MF bands) became a key feature of the newly created radio navigation system for aviation. The low frequency radio range (LFR) network, which consisted of hundreds of Adcock antenna arrays, defined the airways used by aircraft for instrument flying. The LFR remained as the main aerial navigation technology until it was replaced by the VOR system in the 1950s and 1960s.
The Adcock antenna array has been widely used commercially, and implemented in vertical antenna heights ranging from over 40m (130 feet) in the LFR network, to as small as 13cm (5 inches) in tactical direction finding applications (receiving in the UHF band). (Full article...)
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Sketched design of a typical modern-style halo antenna. The sizes of, and space between the round end-plates is adjusted to tune the antenna to resonance; for some halos they are omitted. The thick, black, vertical line is the feed cable, ending in a small black box that contains a trimmer capacitor that with the gamma arm length, impedance matches the antenna feedpoint. A halo antenna, or halo, is a center-fed 1 /2wavelengthdipole antenna, which has been bent into a circle, with a break directly opposite the feed point. The dipole's ends are close, but do not touch, and the ends on either side of the gap may be flared out to form a larger air gap capacitor, whose spacing is used to fine-adjust the antenna's resonant frequency. Most often halos are mounted horizontally, resulting in the antenna's radiation being horizontally polarized and very nearly omnidirectional. (Full article...)
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Main types of parabolic antennas
An offset dish antenna or off-axis dish antenna is a type of parabolic antenna. It is so called because the antenna feed is offset to the side of the reflector, in contrast to the common "front-feed" parabolic antenna where the feed antenna is suspended in front of the dish, on its axis. As in a front-fed parabolic dish, the feed is located at the focal point of the reflector, but the reflector is an asymmetric segment of a paraboloid, so the focus is located to the side.
The purpose of this design is to move the feed antenna and its supports out of the path of the incoming radio waves. In an ordinary front-fed dish antenna, the feed structure and its supports are located in the path of the incoming beam of radio waves, partially obstructing them, casting a "shadow" on the dish, reducing the radio power received. In technical terms this reduces the aperture efficiency of the antenna, reducing its gain. In the offset design, the feed is positioned outside the area of the beam, usually below it on a boom sticking out from the bottom edge of the dish. The beam axis of the antenna, the axis of the incoming or outgoing radio waves, is skewed at an angle to the plane of the dish mouth.
The design is most widely used for small parabolic antennas or "mini-dishes", such as common Ku band home satellite television dishes, where the feed structure is large enough in relation to the dish to block a significant proportion of the signal. Another application is on satellites, particularly the direct broadcast satellites which use parabolic dishes to beam television signals to homes on Earth. Because of the limited transmitter power provided by their solar cells, satellite antennas must function as efficiently as possible. The offset design is also widely used in radar antennas. These must collect as much signal as possible in order to detect faint return signals from faraway targets.
Offset dish antennas are more difficult to design than front-fed antennas because the dish is an asymmetric segment of a paraboloid with different curvatures in the two axes. Before the 1970s offset designs were mostly limited to radar antennas, which required asymmetric reflectors anyway to create shaped beams. The advent in the 1970s of computer design tools which could easily calculate the radiation pattern of offset dishes has removed this limitation, and efficient offset designs are being used more and more widely in recent years. (Full article...)
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A dielectric resonator antenna (DRA) is a radio antenna mostly used at microwave frequencies and higher, that consists of a block of ceramic material of various shapes, the dielectric resonator, mounted on a metal surface, a ground plane. Radio waves are introduced into the inside of the resonator material from the transmitter circuit and bounce back and forth between the resonator walls, forming standing waves. The walls of the resonator are partially transparent to radio waves, allowing the radio power to radiate into space.
An advantage of dielectric resonator antennas is they lack metal parts, which become lossy at high frequencies, dissipating energy. So these antennas can have lower losses and be more efficient than metal antennas at high microwave and millimeter wave frequencies. Dielectric waveguide antennas are used in some compact portable wireless devices, and military millimeter-wave radar equipment. The antenna was first proposed by Robert Richtmyer in 1939. In 1982, Long et al. did the first design and test of dielectric resonator antennas considering a leaky waveguide model assuming magnetic conductor model of the dielectric surface . In that very first investigation, Long et al. explored HEM11d mode in a cylindrical shaped ceramic block to radiate broadside. After three decades, yet another mode (HEM12d) bearing identical broadside pattern has been introduced by Guha in 2012.
An antenna like effect is achieved by periodic swing of electrons from its capacitive element to the ground plane which behaves like an inductor. The authors further argued that the operation of a dielectric antenna resembles the antenna conceived by Marconi, the only difference is that inductive element is replaced by the dielectric material. The configuraiton offers a framework where the geometric symmetry of the electric field in free space is explicitly broken by the floating inductor-capacitor system with one end excited by a time varying voltage source. (Full article...)
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A truncated biconical antenna showing the typical "mace head" shape In radio systems, a biconical antenna is a broad-bandwidth antenna made of two roughly conical conductive objects, nearly touching at their points.
Biconical antennas are broadband dipole antennas, typically exhibiting a bandwidth of three octaves or more. A common subtype is the bowtie antenna, essentially a flattened version of the biconical design which is often used for short-range UHF television reception. These are also sometimes referred to as butterfly antennas.
Diagram of base-fed umbrella antenna. The red cylinders are insulators. Buried under the antenna is a radial wire ground system (not shown). An umbrella antenna is a capacitively top-loaded wire monopole antenna, consisting in most cases of a mast fed at the ground end, to which a number of radial wires are connected at the top, sloping downwards. One side of the feedline supplying power from the transmitter is connected to the mast, and the other side to a ground (earthing) system of radial wires buried in the earth under the antenna. They are used as transmitting antennas below 1MHz, in the MF, LF and particularly the VLF bands, at frequencies sufficiently low that it is impractical or infeasible to build a full size quarter-wave monopole antenna. The outer end of each radial wire, sloping down from the top of the antenna, is connected by an insulator to a supporting rope or cable anchored to the ground; the radial wires can also support the mast as guy wires. The radial wires make the antenna look like the wire frame of a giant umbrella (without the cloth) hence the name. (Full article...)
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The 2006 NASA ST5 spacecraft antenna. This complicated shape was found by an evolutionary computer design program to create the best radiation pattern.
In radio communications, an evolved antenna is an antenna designed fully or substantially by an automatic computer design program that uses an evolutionary algorithm that mimics Darwinianevolution. This procedure has been used since the early 2000s to design antennas for mission-critical applications involving stringent, conflicting, or unusual design requirements, such as unusual radiation patterns, for which none of the many existing antenna types are adequate. (Full article...)
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Array of four axial-mode helical antennas used as a satellite tracking-acquisition antenna, Pleumeur-Bodou, France A helical antenna is an antenna consisting of one or more conducting wires wound in the form of a helix. A helical antenna made of one helical wire, the most common type, is called monofilar, while antennas with two or four wires in a helix are called bifilar, or quadrifilar, respectively.
In most cases, directional helical antennas are mounted over a ground plane, while omnidirectional designs may not be. The feed line is connected between the bottom of the helix and the ground plane. Helical antennas can operate in one of two principal modes: normal or axial.
In the normal mode or broadside helical antenna, the diameter and the pitch of the aerial are small compared with the wavelength. The antenna acts similarly to an electrically shortdipole or monopole, equivalent to a 1/4 wave vertical and the radiation pattern, similar to these antennas is omnidirectional, with maximum radiation at right angles to the helix axis. For monofilar designs the radiation is linearly polarized parallel to the helix axis. These are used for compact antennas for portable hand held as well as mobile vehicle mount two-way radios, and in larger scale for UHF television broadcasting antennas. In bifilar or quadrifilar implementations, broadside circularly polarized radiation can be realized.
In the axial mode or end-fire helical antenna, the diameter and pitch of the helix are comparable to a wavelength. The antenna functions as a directional antenna radiating a beam off the ends of the helix, along the antenna's axis. It radiates circularly polarized radio waves. These are used for satellite communication. Axial mode operation was discovered by physicist John D. Kraus (Full article...)
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Array of four axial-mode helical antennas used as a satellite tracking-acquisition antenna, Pleumeur-Bodou, France A helical antenna is an antenna consisting of one or more conducting wires wound in the form of a helix. A helical antenna made of one helical wire, the most common type, is called monofilar, while antennas with two or four wires in a helix are called bifilar, or quadrifilar, respectively.
In most cases, directional helical antennas are mounted over a ground plane, while omnidirectional designs may not be. The feed line is connected between the bottom of the helix and the ground plane. Helical antennas can operate in one of two principal modes: normal or axial.
In the normal mode or broadside helical antenna, the diameter and the pitch of the aerial are small compared with the wavelength. The antenna acts similarly to an electrically shortdipole or monopole, equivalent to a 1/4 wave vertical and the radiation pattern, similar to these antennas is omnidirectional, with maximum radiation at right angles to the helix axis. For monofilar designs the radiation is linearly polarized parallel to the helix axis. These are used for compact antennas for portable hand held as well as mobile vehicle mount two-way radios, and in larger scale for UHF television broadcasting antennas. In bifilar or quadrifilar implementations, broadside circularly polarized radiation can be realized.
In the axial mode or end-fire helical antenna, the diameter and pitch of the helix are comparable to a wavelength. The antenna functions as a directional antenna radiating a beam off the ends of the helix, along the antenna's axis. It radiates circularly polarized radio waves. These are used for satellite communication. Axial mode operation was discovered by physicist John D. Kraus (Full article...)
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A rabbit ears indoor antenna. This model also has a loop antenna for UHF reception.
Television antennas are manufactured in two different types: indoor and outdoor antennas. Indoor antennas are designed to be located on top of or next to the television set, but are ideally placed near a window in a room and as high up as possible for the best reception. The most common types of indoor antennas are the dipole ("rabbit ears"), which work best for VHF channels, and loop antennas, which work best for UHF. Outdoor antennas on the other hand are designed to be mounted on a mast on top of the owner's house, or in a loft or attic where the dry conditions and increased elevation are advantageous for reception and antenna longevity. Outdoor antennas are more expensive and difficult to install but are necessary for adequate reception in fringe areas far from television stations; the most common types of these are the Yagi, log periodic, and (for UHF) the multi-bay reflective array antenna. (Full article...)
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Typical amateur radio inverted vee installed on roof. This multiband antenna allows transmissions on the 40/20/15/10 meter bands. Center point is held up with masting and ends are secured to roof. Two VHF verticals are also shown. An inverted vee antenna is a type of antenna similar to a horizontal dipole, but with the two sides bent down towards the ground, typically creating a 120- or 90-degree angle between the dipole legs. It is typically used in areas of limited space as it can significantly reduce the ground foot print of the antenna without significantly impacting performance. Viewed from the side, it looks like the English letter "V" turned upside down, hence the name. Inverted vee antennas are commonly used by amateur radio stations, and can be used aboard sailing vessels requiring better HF performance than available with a short whip antenna. Inverted vee antennas are horizontally polarized and have a similar pattern compared to a traditional horizontal dipole. (Full article...)
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Patterned Vivaldi antenna, made from double-sided printed circuit board material A Vivaldi antenna or Vivaldi aerial or tapered slot antenna is a co-planar broadband-antenna, which can be made from a solid piece of sheet metal, a printed circuit board, or from a dielectric plate metalized on one or both sides. The feedline excites an open space via a microstrip line or coaxial cable, and may be terminated with either a sector-shaped area or a direct coaxial connection. From the open space, the signal traverses an exponentially tapered pattern via a symmetrical slot line.
Vivaldi antennas can be made for linear polarized waves or – using two devices arranged in orthogonal direction – for transmitting / receiving both polarization orientations.
If fed with 90° phase-shifted signals, orthogonal devices can transmit/receive circular-oriented electromagnetic waves.
Vivaldi antennas are useful for any frequency, as all antennas are scalable in size for use at any wavelength. Printed circuit technology makes this type antenna cost effective for microwave frequencies 1GHz or higher.
Advantages of Vivaldi antennas are their broadband characteristics (suitable for ultra-wideband signals ), their easy manufacturing process using common methods for PCB production, and their easy impedance matching to the feeding line using microstrip line modeling methods.
The MWEE collection of EM simulation benchmarks includes a Vivaldi antenna.
Several researchers have experimented variations in the shape of the Vivaldi antenna to improve some of its characteristics. An example is the Palm Tree Vivaldi Antenna, with greater gain and directivity, used in Near-Field Microwave Biomedical Imaging Applications. (Full article...)
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Crossed field test antenna installed in Silsden, U.K.
A crossed field antenna (CFA) is a controversial type of radio antenna for long and mediumwavebroadcasting, patented by F. M. Kabbary and M. C. Hately in 1986, which was claimed to have the same efficiency as a conventional antenna but only one-tenth the overall height. The invention was received with incredulity from experts in electromagnetics and antenna technology owing to the deficient theoretical justifications offered and the lack of viable experimental verification. Although the antenna was installed in a few broadcasting stations in the 1990s, performance has not borne out the claims of the inventors. (Full article...)
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X-band slotted waveguide marine radar antenna on ship, 8–12GHz. The antenna radiates a narrow vertical fan-shaped beam of microwaves, scanning the entire 360° water surface around the ship with each rotation.
A slot antenna consists of a metal surface, usually a flat plate, with one or more holes or slots cut out. When the plate is driven as an antenna by an applied radio frequency current, the slot radiates electromagnetic waves in a way similar to a dipole antenna. The shape and size of the slot, as well as the driving frequency, determine the radiation pattern. Slot antennas are usually used at UHF and microwave frequencies at which wavelengths are small enough that the plate and slot are conveniently small. At these frequencies, the radio waves are often conducted by a waveguide, and the antenna consists of slots in the waveguide; this is called a slotted waveguide antenna. Multiple slots act as a directivearray antenna and can emit a narrow fan-shaped beam of microwaves. They are used in standard laboratory microwave sources used for research, UHF television transmitting antennas, antennas on missiles and aircraft, sector antennas for cellular base stations, and particularly marine radar antennas. A slot antenna's main advantages are its size, design simplicity, and convenient adaptation to mass production using either waveguide or PC board technology. (Full article...)
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Before the HRS antenna became the default design for high power broadcasting in the 1950s, Sterba curtains were used to transmit shortwave broadcasts.
Sterba curtains are modest-gain single-band curtain array antennas. They are named after Ernest J. Sterba, who developed a simple shortwave curtain array for Bell Labs in the 1930s. Sterba curtain arrays are described in William Orr's Radio Handbook.
There are multiple feed arrangements for the Sterba curtain arrays, as with HRS type antennas. However, Sterba arrays provide a limited gain-bandwidth system for the demands of modern shortwave broadcasting systems therefore they are significantly less common than more modern options, such as an ALLISS system.
Sterba curtain arrays preceded HRS type antennas by less than a decade. Only about 1% of high power HF broadcasting antennas in use in the 2000s are Sterba type curtain arrays. It is expected that by 2020 that all Sterba type curtain arrays will have been decommissioned.[citation needed] There are noted instances of Sterba arrays still in use by Amateur Radio operators operating on HF bands and transmitting in narrow bandwidths. (Full article...)
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