Dipoles

• "Rabbit ears" dipole variant for VHF television reception
• Two-element turnstile antenna for reception of weather satellite data, 137 MHz. Has circular polarization.

The dipole consists of two conductors, usually metal rods or wires, usually arranged symmetrically, end-to-end, with one side of the balanced feedline from the transmitter or receiver attached to each, and usually elevated as high as feasible above the ground.^{[3][lower-alpha 2]} The most common type, the half-wave dipole, consists of two resonant elements just under a quarter wavelength long. This antenna radiates maximally in directions perpendicular to the antenna's axis, giving it a small directive gain of 2.15 dBi. Although half-wave dipoles are used alone as omnidirectional antennas, they are also a building block of many other more complicated directional antennas.

Turnstile

Two dipole antennas mounted at right angles, fed with a phase difference of 90°. This antenna is unusual in that it radiates in all directions (no nulls in the radiation pattern), with horizontal polarization in directions coplanar with the elements, circular polarization normal to that plane, and elliptical polarization in other directions. Used for receiving signals from satellites, as circular polarization is transmitted by many satellites.

Patch (microstrip)

A type of antenna with elements consisting of metal sheets mounted over a ground plane. Similar to dipole with gain of 6–9 dBi. Integrated into surfaces such as aircraft bodies. Their easy fabrication using PCB techniques have made them popular in modern wireless devices. Often combined into arrays.

Biconical antenna

A dipole with cone-shaped arms, with the feedpoint where their tips meet. They show broader bandwidth than ordinary dipoles, up to three octaves above their base frequency.

Bow-tie antenna

Also called a butterfly antenna – a dipole whose arms are triangular or arrow-shaped (⧓ ⨝ ⪥) with the feedpoint where the tips of the triangles meet. It is a flattened version of a biconical antenna. The triangles can either be cut from sheet metal with solid metal centers (⧓), or two wires with their far ends connected (⨝) outlining the shape of a bow-tie, or with unconnected ends in an "X" shape (⪥).^{[lower-alpha 3]}

Fan dipole

Also called a multi-dipole – a common broadband and / or wideband dipole variant that superficially resembles the bow-tie antenna, but is electrically different. It is a composite of pairs of dipole arms; both arms of one of the dipoles are equal-length, but each dipole pair is a different length from every other pair. The several dipole arms extend away ( ⚞⚟ ⪫⪪ ⫸⫷ ) from the common central connection point of the combined antenna.^{[lower-alpha 4]}

Monopoles

• Quarter-wave whip antenna on an FM radio for 88–108 MHz
• Rubber ducky antenna on 446 MHz UHF walkie-talkie with rubber cover removed.
• VHF ground plane antenna
• Mast radiator antenna of medium wave AM radio station, Germany
• 'T' antenna of amateur radio station, 80 ft high, used at 1.5 MHz.
• Folded unipole antenna with a solid metal mast surrounded by six skirt wires, held away by insulated standoffs

A monopole antenna is a half-dipole (see above); it consists of a single conductor such as a metal rod, usually mounted over the ground or an artificial conducting surface (a so-called ground plane).^[3][6] They are sometimes classed together with dipoles (see above) in the broader category of linear antennas, or more plainly straight wire antennas, since their radiating section is normally a straight (linear) wire or aluminum tubing; rarely, both dipoles and monopoles are called electric antennas, since they interact with the electric field of a radio wave, to contrast them against all sizes of loops, which are correspondingly magnetic antennas.^{[lower-alpha 5]}

One side of the feedline from the receiver or transmitter is connected to the conductor, and the other side to ground or the artificial ground plane. The radio waves from the monopole reflected off the ground plane appear as if they came from a fictitious image antenna seemingly below the ground plane, with the monopole and its phantom image effectively forming a dipole. Hence, the monopole antenna has a radiation pattern identical to the top half of the pattern of a similar dipole antenna, and a radiation efficiency a bit less than half of the dipole. Since all of the equivalent dipole's radiation is concentrated in a half-space, the antenna has twice (3 dB increase of) the gain of a similar dipole, neglecting power lost in the ground plane.

The most common form is the quarter-wave monopole which is one-quarter of a wavelength long and has a gain of 5.12 dBi when mounted over a ground plane. Single monopoles have an omnidirectional radiation pattern, so they are used for broad coverage of an area, and have vertical polarization. To reduce signal absorption by the Earth, ground waves used for broadcasting at low frequencies must be vertically polarized, so large vertical monopole antennas are used for broadcasting in the MF, LF, and VLF bands. Small monopoles ("whips") are used as nondirectional antennas on portable radios in the HF, VHF, and UHF bands.

Whip

Type of antenna used on mobile and portable radios in the VHF and UHF bands such as FM "boom boxes", consists of a flexible rod, often made of telescoping segments. In the HF band, "whip" typically refers to an antenna that is too short to resonate naturally; when a whip is long enough to self-resonate (a quarter wavelength or more), it is instead usually just called by the generic name "monopole".

"Rubber ducky"

More formal technical name is normal-mode helix. Most common antenna used on portable two-way radios and cordless phones due to its compactness. Consists of an electrically short wire helix. The helical shape adds inductance to cancel the capacitive reactance of the short radiator, making it resonant. Like all electrically short antennas it is nearly isotropic – has very low gain. Not to be confused with the much larger axial mode helix (see below).^{[lower-alpha 6]}

Ground plane antenna

A whip antenna with several rods extending horizontally from base of the whip, attached to the ground side of the feedline. Since the whip is mounted above ground, the horizontal rods form an elevated ground plane just below the whip to reflect its radiation away from the earth and increase its gain. Used for elevated base station antennas for land mobile radio systems such as police, ambulance, and taxi dispatchers.

Mast radiator

A radio tower in which the tower structure itself serves as the antenna. Common form of transmitting antenna for AM radio stations and other MF and LF transmitters. At its base the tower is usually, but not necessarily, mounted on a ceramic insulator to isolate it from the ground.

Folded unipole antenna

A modified mast antenna, usually grounded at its base, augmented by one or several parallel wires called "skirt wires" that attach to the mast part-way up the antenna. The skirt wires can attach at any height between part-way up and the top of the mast. One or more of the skirt wires is fed with the signal, similar to a gamma match. The number and relative thickness of the mast and the skirt wires adjusts the feedpoint impedance.^{[lower-alpha 7]}

'T' antenna

Consists of a long horizontal wire suspended between two towers with insulators, with a vertical wire hanging down from it, attached to a feedline to the receiver or transmitter on one feed wire and the other to a required low resistance ground. The dangling vertical wire is the radiating part of the antenna; normally it is shorter than the quarter wavelength required for resonance. For the 'T' antenna, the dangling wire attaches in the exact center of the top wire. Used on MF and the lower HF bands. Since at these frequencies the vertical wire is electrically short – much shorter than a quarter wavelength – the horizontal wire serves as a "capacitance hat" to increase the current in the vertical radiator, increasing the efficiency and gain. Since equal horizontal currents travel in opposite directions away from the center of the top wire, those currents balance and produce essentially no radiation. Usually the horizontal section is not long enough to supply sufficient capacitance, so the antenna feedpoint requires a loading coil to tune out any remaining reactance, and the tuned antenna will have narrow bandwidth. When the "capacitance hat" is wide enough to compensate for the missing length on the vertical wire, a 'T' antenna's performance can come close to a full-size monopole.

Inverted 'L'

Similar in construction to a 'T' antenna described above, but with the dangling vertical wire attached to one end of the horizontal wire instead of the center. The altered connection point gives the antenna the shape of the Greek letter Γ. Unlike the 'T' antenna, both the vertical and horizontal wires radiate, with their respective radiation being vertically and horizontally polarized, and their combined radiation diagonally polarized, usually at a steep angle. Although all parts of the antenna radiate, the strongest radiation comes from the vertical wire, so the horizontal wire serves both as a "capacitance hat" and as a weak radiator. If the length of the horizontal wire is sufficient to make the total length of wire about a quarter wavelength, the inverted-L's performance can come close to a full-size monopole.

Inverted 'F'

Combines the advantages of the compactness of inverted-L antenna, and the good matching of the unipole antenna. The antenna is grounded at the base and fed at some intermediate point. The position of the feed point determines the antenna impedance. Thus, matching can be achieved without the need for a separate matching network. Effectively a shunt-fed inverted-L, with the feed point attached to the horizontal wire rather than the vertical, giving the antenna the shape of the line-drawing character ╓, or the Hangul letter ﾢ.

Umbrella

An elaborated and enlarged version of a 'T' antenna; it is a very large wire transmitting antenna with extremely narrow bandwidth, used on VLF bands for VLF time signals or long-range submarine communications. Relative to the even larger wavelengths it is used for, it is paradoxically an ultra-short antenna. It consists of a central radiating tower with multiple wires attached at the top, extending out radially from the mast and insulated at the ends, resembling a metal umbrella frame. Like other ultra-short antennas it has an extremely high capacitive reactance and minimal radiation resistance, which require a large loading coil and low-resistance counterpoise system.

Loop antennas

Loop antennas consist of a loop (or coil) of wire. Loop antennas interact directly with the magnetic field of the radio wave, rather than its electric field as linear antennas do; for that reason they are on rare occasions categorized as magnetic antennas, but that generic name is confusingly similar to the term magnetic loop used to describe small loops.^{[lower-alpha 5]} Their exclusive interaction with the magnetic field makes them relatively insensitive to electrical noise within about 1/ 6  wavelength of the antenna,^[3][7][2] and more tolerant of being mounted close to the ground, since for most soils the earth is closer to being somewhat radio-transparent to the magnetic part of mediumwaves and longer shortwaves, than is the case for their electric part. There are essentially two broad categories of loop antennas: large loops (or full-wave loops) and small loops. Only one design, a halo antenna, that is normally called a loop does not clearly fit exclusively into either the large or small loop categories.

Array antenna

• VHF collinear array of folded dipoles
• Yagi–Uda television antenna for analog channels 2–4, 47–68 MHz
• Log-periodic dipole array covering 140–470 MHz
• Sector antennas (white bars) on cell phone tower. Collinear arrays of dipoles, these radiate a flat, fan-shaped beam.
• Reflective array UHF TV antenna, with bowtie dipoles to cover the UHF 470–890 MHz band
• US Air Force PAVE PAWS phased array radar antenna for ballistic missile detection, Alaska. The two circular arrays are each composed of 2677 crossed dipole antennas.
• Curtain array shortwave transmitting antenna, Austria. Wire dipoles suspended between towers.
• Four-bay batwing television broadcasting antenna, Germany

Array antennas are composites of multiple simple antennas, either linear, or loops, or combinations of each. The multiple parallel-aligned simple antennas work together as a single compound antenna; they are the RF analogs of compound optical lenses made from combinations of simple lenses. The constituent simple antennas can be dipoles, monopoles, or loops, or mixed loops and dipoles. Broadside arrays consist of multiple identical driven elements, usually dipoles, fed in phase, radiating a beam perpendicular to the plane containing the simple antennas. Endfire arrays are fed out-of-phase, with the phase difference corresponding to the distance between them; they radiate parallel to the plane that the consitituent antennas all lie in.^{[3][9][4](pp283–371)} Parasitic arrays consist of multiple antennas, usually dipoles, with one driven element and the rest parasitic elements, which radiate a beam along the line of the antennas.

Vertical collinear

Consists of several dipoles fed in phase, with their axēs stacked atop each other, in a single vertical line. It is a high-gain omnidirectional antenna, meaning more of the power is radiated in horizontal directions and less wasted radiating up into the sky or down onto the ground. Gain of 8–10 dBi. Used as base station antennas for land mobile radio systems such as police, fire, ambulance, and taxi dispatchers, and sector antennas for cellular base stations.

Yagi–Uda

Also called a "Yagi", it is one of the most common directional antennas at UHF, VHF, and upper HF frequencies. Consists of multiple half-wave dipole elements aligned with their axēs parallel, in the same plane, with a single resonant-length driven element wired to the feedline, usually the next-to-last, next-to-longest element in the array.^{[lower-alpha 12]} The multiple other elements are parasitic, which reflect and direct the radiated signal into a single direction, hence a beam antenna.^{[lower-alpha 13]} The simple antennas used to make a Yagi-Uda can either all be linear or bent linear antennas, or all loops (a quad antenna) or (rarely) a mixed combination of loops and straight-wire antennas.

Yagi–Udas are used for rooftop television antennas, point-to-point communication links, and long distance shortwave communication using skywave ("skip") reflection from the ionosphere. They typically have gains between 10–20 dBi depending on the number of director elements used, but their bandwidths are very narrow.^{[lower-alpha 14]}

Moxon antenna

Also called a Moxon rectangle; it is a rectangular-shaped, folded version of a two-element Yagi-Uda.^[10]

Adcock antenna

An array of four parallel dipole (or monopole) antennas, all equal size and equidistant, aligned vertically at four corners of a square. All four dipoles are driven, but with opposing phases for adjacent dipole elements. The spacing and phasing of the dipole elements makes the combination of the arrayed elements moderately directional.

Log-periodic dipole array

Sometimes called a "fishbone" antenna. It consists of many dipole elements along a boom with gradually increasing lengths, all connected to the transmission line with alternating polarity. It is a directional antenna with a wide bandwidth, which makes it ideal for use as a rooftop television antenna, although its gain is much less than a Yagi of comparable size.^{[lower-alpha 12]} For long wavelengths in the lower HF band the array may be made of ground-mounted monopoles instead of dipoles.

Reflective array

Multiple dipoles in a two-dimensional array mounted in front of a flat reflecting screen. Used for radar and UHF television transmitting and receiving antennas.

Phased array

is a high gain antenna used at UHF and microwave frequencies which is electronically steerable. It consists of multiple dipoles in a two-dimensional array, each fed through an electronic phase shifter, with the phase shifters controlled by a computer control system. The beam can be instantly pointed in any direction over a wide angle in front of the antenna. Used for military radar and jamming systems.

Curtain array

is a large directional wire transmitting antenna used at HF by shortwave broadcasting stations. It consists of a vertical rectangular array of identical wire dipoles suspended in a parallel row in front of a flat reflector screen, consisting of a second row of vertical parallel "curtain" wires, all supported between two metal towers. It radiates a horizontal beam of radio waves into the sky above the horizon, which is reflected by the ionosphere to Earth beyond the horizon.

Half-square

A pair of quarter-wave inverted vertical monopoles, whose bases are not connected to the ground, and whose tops are connected by a wire one half-wavelength long, which serves as both a counterpoise and a crossover feedline. The verticals are the radiators and function as a two-element array, similar to the bobtail curtain; each radiator's nominal feedpoint is at its top, rather than at the base. The structure is shaped like the Greek letter Π (not to be confused with the Half-Loop antenna described below).^{[lower-alpha 9]} The top-to-top connecting wire serves as a phased feedline, or an auxiliary feed, which puts the point of maximum current at the top of each monopole. Neither monopole element has a wire connection to the ground beneath it, although there typically is considerable capacitive coupling, which can be exploited to shorten the verticals. Top-fed inverted monopoles produce a strong signal lower to the horizon than an ordinary bottom-fed monopole, since the latter's signal must angle up more from ground-level to get past nearby obstructions. Despite the verticals themselves being fed from their tops, the feedpoint for the combined system may be placed at any of several locations – often at the center of the horizontal wire.^[8]

Batwing

Also called a superturnstile, is a specialized antenna used in television broadcasting consisting of perpendicular pairs of dipoles with radiators resembling bat wings. The batwing shape gives them the wide bandwidth needed for whole-channel transmission. Typically several batwing antennas are stacked vertically on a mast to make VHF television broadcast antennas. Omnidirectional radiation pattern with high gain in horizontal directions.

Microstrip

A microwave antenna that can achieve large gains in compact space; an array of patch antennas on a substrate fed by microstrip feedlines. Ease of fabrication by PCB techniques have made them popular in modern wireless devices. Beamwidth and polarization can be actively reconfigurable.

Aperture antenna

• NASA Cassegrain, Extremely high gain ~70 dBi.
• Corner reflector UHF TV antenna with "bowtie" dipole driven element at its center.
• Microwave horn antenna bandwidth 0.8–18 GHz.
• X band marine radar slot antenna on ship, 8–12 GHz.
• Dielectric lens antenna used in millimeter wave radio telescope.

An aperture antenna consists of a small dipole or loop feed antenna embedded inside a larger, three-dimensional surrounding structure that guides the radio waves from the feed antenna in a particular direction, and vice versa. The guiding structure is often dish-shaped or funnel-shaped, and quite large compared to a wavelength, with an opening, or aperture, to emit the radio waves in only one direction. Since the outer antenna structure is itself not resonant, it can be used for a wide range of frequencies, by replacing or retuning the inner feed antenna, which normally is resonant.

Corner reflector

A directive antenna with moderate gain of about 8 dBi often used at UHF frequencies. Consists of a dipole mounted in front of two reflective metal screens joined at an angle, usually 90°. Used as a rooftop UHF television antenna and for point-to-point data links.

Parabolic

The most widely used high gain antenna at microwave frequencies and above. Consists of a dish-shaped metal parabolic reflector with a feed antenna at the focus. It can have some of the highest gains of any antenna type, up to 60 dBi, but the dish must be large compared to a wavelength. Used for radar antennas, point-to-point data links, satellite communication, and radio telescopes.

Horn

A horn antenna has a flaring metal horn attached to a waveguide. It is a simple antenna with moderate gain of 15 to 25 dBi, used for applications such as radar guns, radiometers, and as feed antennas for parabolic dishes.

Slot

Consists of a waveguide with one or more slots cut in it to emit the microwaves. Linear slot antennas emit narrow fan-shaped beams. Used as UHF broadcast antennas and marine radar antennas.

Lens

A lens antenna is made from a layer of dielectric, or a metal screen, or multiple waveguide structure of varying thickness, in front of a feed antenna, which acts as a lens which refracts the radio waves, focusing them on the feed antenna.

Dielectric resonator

Consists of small ball or puck-shaped piece of dielectric material excited by aperture in waveguide Used at millimeter wave frequencies