Antenna types

This article gives a list of brief summaries of multiple different types of antennas used for radio receiving or transmitting systems. Antennas are typically grouped into categories based on their electrical operation; the classifications and sub-classifications below follow those used in most antenna engineering textbooks.

Categorizing antennas and organization of article sections

This section is an overview that lists the following sections and subsections in this article, in the order that those sections occur. Each group of antennas fit together based on some commonly used electrical operating principle: There is at least one aspect for which each group of antennas all work in the same way.
The list below summarizes the parts of this article; the bold-face links in this subsection lead to the other article sections and subsections, each of which gives a summary description. In turn, the links within those summaries lead to relevant Wikipedia articles on antennas.
The listed antennas are clustered based on some shared principle of electrical operation, so that antenna designs that use similar functional principles are listed close together. The order used is neither objective nor universal, but does conform to the organization used by many authors.
Antennas can be classified in various ways, and various writers organize the different aspects of antennas with different priorities, depending on whether their text is most focused on specific frequency bands; or antenna size, construction, and placement feasibility; or explicating principles of radio theory and engineering that underlie, guide, and constrain antenna design.
Further, different types of antennas are made with properties especially optimized for particular uses, and the electrical design of antennas serves as a way to group them:

Most often, the greatest design constraint is the size of the radio waves the antenna is to intercept or emit.
A competing second influence is optimization criteria for either receiving or for transmitting; the distinction has practical differences for the middle shortwaves and all longer wavelengths.
A competing third criterion is the number and bandwidth of the that a single antenna intercepts or emits.
A fourth design goal is to make the antenna directional: To project radio waves toward or intercept radio waves from only one direction as exclusively as possible.

; [|Simple antennas] : There are three types of "simple antennas": [|dipoles], [|monopoles], and [|loops]. The three simple antenna types are all typically used for transmission on frequencies where they self-resonate, however, resonance is often not critical for receiving, and typically merely a convenience rather than a necessity for transmission. "Simple" antennas are also used as building-blocks for the more complicated antenna types, such as [|composite antennas], which is analogous to assembling a combination of several simple optical lenses to make a single compound lens. Simple antennas are usually further subdivided into
; [|Composite antennas] : Composite antennas are made by combining one or more simple antenna either with other simple antenna or with some kind of a metallic / conductive reflecting surface formed into a screen, or metallic curtain, or curved dish. Usually only one of the component antennas is resonant on the design frequency, and in that typical case, the feedline connects only to the resonant component.
; [|Traveling wave antennas] : Traveling wave antennas are made from long wires, not far above ground and aligned in the direction from which signals are desired; also sometimes zig-zagging pairs of alternately diverging and converging wires are used, whose center-line aims in the desired receive direction. Traveling wave antennas are notable for being one of the few types of antennas that are normally not self resonant: Electrical waves induced by received radio waves travel through the antenna wire in the direction that the arriving RF signals are travelling. Only electrical waves traveling toward the feedpoint are collected; waves traveling away from the feedpoint are grounded through a terminating resistor at the end of the wire opposite the feedpoint. The resistive termination makes the antenna receive in only one direction; in their function, they achieve goals similar to an [|aperture antenna] but traveling wave antennas are much simpler, so much easier to build. In order to make them even more directional, they are made several wavelengths long, hence unsteerable. Absorption in the terminating resistor makes them inefficient radiators, but still sometimes used for transmitting since they work on any frequency.
; [|"Other" antennas] : Some antennas don't comfortably fit in the categories used here, so this article's last section for real antennas is an "everything else" category for a few that aren't clearly one of the types of antennas listed here. For example, random wire antennas, and antennas that are laid down on the ground, instead of being raised high in the air, as normal antennas are.
; [|Isotropic antenna] : The last section is for a unique type of "fake" antenna, called an isotropic antenna or isotropic radiator. It is a convenient fiction used as a "worst possible case" that real antennas' directivity is compared to.

Simple antennas

The category of simple antennas consists of dipoles, monopoles, and loop antennas. Nearly all can be made with a single segment of wire.
Dipoles and monopoles are called linear antennas since their radiating parts lie along a single straight line – ignoring convenience bends at the far ends, if any. On rare occasions they are called electric antennas since they engage with the electric part of RF radiation, in contrast to loops, which correspondingly are magnetic.
The term "linear" used to describe the typical shape of these antennas is not a strict criterion for the category: End-sections of a so-called "linear" antenna that are far from its center can be bent away from a straight line with hardly any noticeable electrical consequences; sag is common and comfortably tolerated in the nominally "straight" antennas; finally, in some varieties of "linear" dipoles, the two arms or "poles" can be bent into a "V" shape, even though each individually may be a mostly straight line.

Dipoles

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.
Some varieties of dipoles differ only in having off-center feedpoints or feedpoints at their ends, others vary the alignment or shape of the dipole arms. Although dipoles are used alone as omnidirectional antennas, they are also a building block of many other more complicated directional antennas. All types of dipoles can be mounted either vertically or horizontally, and the chosen orientation determines their receive / transmit directions
and wave polarity.
; Half-wave dipole: The most common type of dipole consists of two resonant elements, each just under a quarter wavelength long, hence a total length of about a half-wave. This antenna radiates maximally in directions perpendicular to the antenna's axis, giving it a small directive gain of 2.15 dBi.
; Doublet : "Doublet" is a name radio amateurs sometimes use for a dipole antenna that is used on a frequency below the antenna's lowest self-resonance. It is not necessary for an antenna to be resonant to transmit well, rather resonance is preferred to easily feed power to it; using a transmatch may make feeding power to an antenna on its non-resonant frequencies possible. Some "doublets" are carefully sized to avoid resonance – and especially "antiresonances" – in order to make impedance matching for multiple frequencies less challenging.
; Folded dipole : A typical folded dipole is two half-wave dipoles mounted parallel to each other, a few inches apart, with the far ends connected. Only one of the dipoles is fed, and the second dipole connects straight through the center where the first has the usual feedpoint. The two-wire version is often described as a "squashed loop antenna", since the total length of wire is one wavelength, and efficiency / feedpoint impedance of the folded dipole is very high: 4× that of a single dipole, analogous to the high efficiency of large loops. Any number of similar parallel wires may be added, with the efficiency rising as the square of the number of parallel wires; hence a three-wire folded dipole would a 9× greater impedance.
; 'V' antenna : When the two arms of a dipole are individually straight, but bent towards each other in a 'V' shape, at an angle noticeably less than 180°, the dipole is called a 'V' antenna. When the ends of the dipole's arms are about level with the branch point, it is called a flat 'V', or a horizontal 'V'; when its ends are much closer to the ground than their center branch-point, the antenna is called an inverted 'V'. The inverted 'V' is popular since it provides some of the good electrical performance of a dipole, but only requires one high mounting point, whereas an ordinary dipole requires at least two, often three. Due to a mixture of direct radiation and ground reflected radiation, the inverted-'V' tends to be mostly omnidirectional, but depending on the center angle, can slightly favor the direction along the midline between the two arms of the 'V'.
; Sloper : A sloper or sloper dipole is a half-wave wire slanting down from a single elevated mounting point. It is usually fed at its center with the feedline cable itself slanting away at a perpendicular counter-slope from the sloping antenna wire, towards a small pole or a ground anchor near the base of the mast. The sloper's far end is attached to a short pole or fastened by an insulated cord to a ground anchor. It is popular because it requires only a single mast, and with a good ground system below it, has a nearly omnidirectional pattern.
; Modern Windom antenna : More formally called an off-center-fed dipole. The modern "Windom" is a dipole which is fed approximately one third of the distance from one of its ends, but otherwise erected like an ordinary dipole, including most dipole variations. The strategically chosen offset feed location has a fairly high impedance, but fortuitously shows roughly the same high impedance on most of its harmonics. The Windom antenna is popular because it has all of the advantages of an ordinary dipole, but functions well on almost twice as many shortwave frequencies as an identical sized center-fed dipole. The price for the extra working frequencies is the needed to match a feed impedance 5–7 times higher than the standard 50 Ohm transmitter impedance.
; End-fed dipole : A dipole can be fed from very near its end but at the ends, the impedances are exceedingly high – a few thousands of ohms, depending on the average height of the antenna and thickness of its wire. The end location has an inconveniently extreme impedance, but it is roughly the same high impedance for all the harmonics, and accommodation for any one harmonic will be near to right for all the other harmonics. The benefit of the extensive measures needed for matching to the high impedance is that the antenna can then function well on every harmonic, and hence can be used for transmitting on exactly twice as many frequencies as a same-size center-fed dipole.
; Turnstile : A turnstile antenna is made of 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, 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 used by most satellites for both transmit and receive, and since it can emit and receive signals in all directions, can operate from a simple, fixed mount, without needing to be aimed or steered towards the target satellite.
; Patch : A patch antenna, or strip antenna, or microstrip, is a type of antenna with elements consisting of a shaped sheet of metal mounted over a second sheet that serves as the antenna's ground plane. The upper sheet is the radiating part of the antenna; it often has small, carefully sized and arranged holes cut into it that improve performance. Often, several parallel mounted strip antennas are combined into an array antenna. When used on airplanes the plane's skin serves as the ground plane, but is normally countersunk into the aircraft body so the overlying antenna strip can sit flush with the plane's metallic surface, to keep it aerodynamically smooth. The gap between the upper surface of the antenna and the plane's metal skin is then rimmed by a narrow, flight-worthy insulating material that seals the gap and securely holds the upper strip. Consequently, a surface-mounted strip antenna looks like a patch on the airplane body, hence the name. The performance of a patch antenna is similar to an ordinary dipole of the same length, with gain of 6–9 dBi. Small size for UHF and easy fabrication have made patch antennas popular in modern wireless devices, using parallel metal-plated sections on a printed circuit board's upper and lower surfaces for the radiating strip and its underlying ground plane.
; Biconical antenna : A biconical is a dipole with cone-shaped arms, with the feedpoint where their tips meet; they are sometimes called "fat dipoles" or "double bowling pins". Biconicals show broader bandwidth than ordinary dipoles, up to three octaves above their base frequency. The monopole version is called a discone antenna.
; Bow-tie antenna : A "bow-tie" antenna is a flattened version of a biconical antenna, with similar broad-band advantages. Also called butterfly antennas, they are dipoles with arms shaped like triangles or arrow-heads ; the antenna feedpoint is where the tips of the triangles meet. The triangles can either be a metal sheet 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.