World Library  
Flag as Inappropriate
Email this Article

Antenna (radio)

Article Id: WHEBN0000187317
Reproduction Date:

Title: Antenna (radio)  
Author: World Heritage Encyclopedia
Language: English
Subject: Radio, Dipole antenna, Near and far field, Feed line, Fractal antenna
Collection: Antennas (Radio), Radio Electronics
Publisher: World Heritage Encyclopedia

Antenna (radio)


Antennas are essential components of all equipment that uses radio. They are used in systems such as radio broadcasting, broadcast television, two-way radio, communications receivers, radar, cell phones, and satellite communications, as well as other devices such as garage door openers, wireless microphones, Bluetooth-enabled devices, wireless computer networks, baby monitors, and RFID tags on merchandise.


Antennas can be designed to transmit and receive radio waves in all horizontal directions equally (omnidirectional antennas), or preferentially in a particular direction (directional or high gain antennas). In the latter case, an antenna may also include additional elements or surfaces with no electrical connection to the transmitter or receiver, such as parasitic elements, parabolic reflectors or horns, which serve to direct the radio waves into a beam or other desired radiation pattern.




  • Terminology 1
  • Overview 2
  • Reciprocity 3
  • Characteristics 4
    • Resonant antennas 4.1
      • Current and voltage distribution 4.1.1
      • Bandwidth 4.1.2
    • Gain 4.2
    • Effective area or aperture 4.3
    • Radiation pattern 4.4
    • Field regions 4.5
    • Impedance 4.6
    • Efficiency 4.7
    • Polarization 4.8
    • Impedance matching 4.9
  • Antenna types 5
    • Monopole 5.1
    • Dipole 5.2
    • Array 5.3
    • Loop 5.4
    • Aperture 5.5
    • Traveling wave 5.6
  • Effect of ground 6
  • Mutual impedance and interaction between antennas 7
  • Gallery 8
    • Antennas and supporting structures 8.1
    • Diagrams as part of a system 8.2
  • See also 9
  • Notes 10
  • References 11
    • General references 11.1
    • "Practical antenna" references 11.2
    • Theory and simulations 11.3
    • Patents and USPTO 11.4
  • Further reading 12


Electronic symbol for an antenna


The origin of the word antenna relative to wireless apparatus is attributed to Italian radio pioneer Guglielmo Marconi. In the summer of 1895, Marconi began testing his wireless system outdoors on his father's estate near Bologna and soon began to experiment with long wire "aerials". Marconi discovered that by raising the "aerial" wire above the ground and connecting the other side of his transmitter to ground, the transmission range was increased.[5] Soon he was able to transmit signals over a hill, a distance of approximately 2.4 kilometres (1.5 mi).[6] In Italian a tent pole is known as l'antenna centrale, and the pole with the wire was simply called l'antenna. Until then wireless radiating transmitting and receiving elements were known simply as aerials or terminals.

Because of his prominence, Marconi's use of the word antenna (Italian for pole) spread among wireless researchers, and later to the general public.[7][8][9]


An antenna, in converting radio waves to electrical signals or vice versa, is a form of transducer.[10]



Whip antenna on car, common example of an omnidirectional antenna





Half-wave dipole antenna





Rooftop television Yagi-Uda antennas like these six are widely used at VHF and UHF frequencies.









It is a fundamental property of antennas that the electrical characteristics of an antenna described in the next section, such as gain, radiation pattern, impedance, bandwidth, resonant frequency and polarization, are the same whether the antenna is transmitting or receiving.[13][14] For example, the "receiving pattern" (sensitivity as a function of direction) of an antenna when used for reception is identical to the radiation pattern of the antenna when it is driven and functions as a radiator. This is a consequence of the reciprocity theorem of electromagnetics.[14] Therefore, in discussions of antenna properties no distinction is usually made between receiving and transmitting terminology, and the antenna can be viewed as either transmitting or receiving, whichever is more convenient.

A necessary condition for the aforementioned reciprocity property is that the materials in the antenna and transmission medium are linear and reciprocal. Reciprocal (or bilateral) means that the material has the same response to an electric current or magnetic field in one direction, as it has to the field or current in the opposite direction. Most materials used in antennas meet these conditions, but some microwave antennas use high-tech components such as isolators and circulators, made of nonreciprocal materials such as ferrite.[13][14] These can be used to give the antenna a different behavior on receiving than it has on transmitting,[13] which can be useful in applications like radar.






Resonant antennas


While there are broadband traveling wave antennas such as the Beverage which do not work by resonance, the vast majority of antennas are based on the monopole or dipole antenna which function as resonators. At a particular frequency, their resonant frequency, waves of current and voltage bouncing back and forth between their ends create standing waves, thus these antennas function best at frequencies near their resonant frequency . The half-wave dipole is probably the most widely used antenna element. At its resonant frequency, the wavelength (figured by dividing the speed of light by the resonant frequency) is slightly over twice the length of the half-wave dipole (thus the name). The quarter-wave monopole antenna consists of one arm of a half-wave dipole, with the other arm replaced by a connection to ground or an equivalent ground plane (or counterpoise). A Yagi-Uda array consists of a number of resonant dipole elements, only one of which is directly connected to the transmission line. The quarter-wave elements of a dipole or vertical monopole imitate a series-resonant electrical element due to the standing wave present along the conductor. At the resonant frequency, the standing wave has a current peak and voltage node (minimum) at the feed-point, thus presenting a lower impedance than at other frequencies. What's more, the large current and small voltage are in phase at that point, resulting in a purely resistive impedance, whereas away from the design frequency the feed-point impedance both rises and becomes reactive. Contrary to an ideal (lossless) series-resonant circuit, a finite resistance remains (corresponding to the relatively small voltage at the feed-point) due to the antenna's radiation resistance (as well as any actual electrical losses).



Current and voltage distribution











Gain is a parameter which measures the degree of directivity of the antenna's radiation pattern. A high-gain antenna will radiate most of its power in a particular direction, while a low-gain antenna will radiate over a wider angle. The antenna gain, or power gain of an antenna is defined as the ratio of the intensity (power per unit surface area) \scriptstyle I radiated by the antenna in the direction of its maximum output, at an arbitrary distance, divided by the intensity \scriptstyle I_\text{iso} radiated at the same distance by a hypothetical isotropic antenna which radiates equal power in all directions. This dimensionless ratio is usually expressed logarithmically in decibels, these units are called "decibels-isotropic" (dBi)

G_\text{dBi} = 10\log{I \over I_\text{iso}}\,

A second unit used to measure gain is the ratio of the power radiated by the antenna to the power radiated by a half-wave dipole antenna \scriptstyle I_\text{dipole}; these units are called "decibels-dipole" (dBd)

G_\text{dBd} = 10\log{I \over I_\text{dipole}}\,


G_\text{dBi} = G_\text{dBd} + 2.15\,


Effective area or aperture



A_{\mathrm{eff}} = {\lambda^2 \over 4 \pi} \, G


Radiation pattern




Field regions














The polarization of an antenna refers to the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation; note that this designation is totally distinct from the antenna's directionality. Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally. As a transverse wave, the magnetic field of a radio wave is at right angles to that of the electric field, but by convention, talk of an antenna's "polarization" is understood to refer to the direction of the electric field.

Reflections generally affect polarization. For radio waves, one important reflector is the ionosphere which can change the wave's polarization. Thus for signals received following reflection by the ionosphere (a skywave), a consistent polarization cannot be expected. For line-of-sight communications or ground wave propagation, horizontally or vertically polarized transmissions generally remain in about the same polarization state at the receiving location. Matching the receiving antenna's polarization to that of the transmitter can make a very substantial difference in received signal strength.

Polarization is predictable from an antenna's geometry, although in some cases it is not at all obvious (such as for the quad antenna). An antenna's linear polarization is generally along the direction (as viewed from the receiving location) of the antenna's currents when such a direction can be defined. For instance, a vertical whip antenna or Wi-Fi antenna vertically oriented will transmit and receive in the vertical polarization. Antennas with horizontal elements, such as most rooftop TV antennas in the United States, are horizontally polarized (broadcast TV in the U.S. usually uses horizontal polarization). Even when the antenna system has a vertical orientation, such as an array of horizontal dipole antennas, the polarization is in the horizontal direction corresponding to the current flow. The polarization of a commercial antenna is an essential specification.

Polarization is the sum of the E-plane orientations over time projected onto an imaginary plane perpendicular to the direction of motion of the radio wave. In the most general case, polarization is elliptical, meaning that the polarization of the radio waves varies over time. Two special cases are linear polarization (the ellipse collapses into a line) as we have discussed above, and circular polarization (in which the two axes of the ellipse are equal). In linear polarization the electric field of the radio wave oscillates back and forth along one direction; this can be affected by the mounting of the antenna but usually the desired direction is either horizontal or vertical polarization. In circular polarization, the electric field (and magnetic field) of the radio wave rotates at the radio frequency circularly around the axis of propagation. Circular or elliptically polarized radio waves are designated as right-handed or left-handed using the "thumb in the direction of the propagation" rule. Note that for circular polarization, optical researchers use the opposite right hand rule from the one used by radio engineers.

It is best for the receiving antenna to match the polarization of the transmitted wave for optimum reception. Intermediate matchings will lose some signal strength, but not as much as a complete mismatch. A circularly polarized antenna can be used to equally well match vertical or horizontal linear polarizations. Transmission from a circularly polarized antenna received by a linearly polarized antenna (or vice versa) entails a 3dB reduction in signal-to-noise ratio as the received power has thereby been cut in half.

Impedance matching






Antenna types

Antennas can be classified in various ways. The list below groups together antennas under common operating principles, following the way antennas are classified in many engineering textbooks.[17][18][19]

Isotropic: An isotropic antenna (isotropic radiator) is a hypothetical antenna that radiates equal signal power in all directions. It is a mathematical model that is used as the base of comparison to calculate the gain of real antennas. No real antenna can have an isotropic radiation pattern. However approximately isotropic antennas, constructed with multiple elements, are used in antenna testing.

The first four groups below are resonant antennas; when driven at their resonant frequency their elements act as resonators. Waves of voltage and current bounce back and forth between the ends, creating standing waves in the metal elements, increasing output power


Monopole antennas consist of a single radiating element such as a metal rod, often mounted over a conducting surface, a ground plane.[18][20] One side of the feedline from the receiver or transmitter is connected to the rod, and the other side to the ground plane, which may be the Earth. 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. Monopoles have an omnidirectional radiation pattern, so they are used for broad coverage of an area, and have vertical polarization. The 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 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 boom boxes, consists of a flexible rod, often made of telescoping segments.
  • 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 mounted on a ceramic insulator to isolate it from the ground.
  • T and inverted L - Consist 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. Used on LF and VLF bands. The vertical wire serves as the radiator. Since at these frequencies the vertical wire is electrically short, much shorter than a quarter wavelength, the horizontal wire(s) serve as a capacitive "hat" to increase the current in the vertical radiator, increasing the gain. Very narrow bandwidth, requires loading coil to tune out the capacitive reactance and make it resonant. Requires low resistance ground (electricity)
  • Inverted F - Combines the advantages of the inverted-L antenna and the F-type antenna of, respectively, compactness and good matching. 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 an extraneous matching network.
  • Umbrella - Very large wire transmitting antennas used on VLF bands. Consists of a central mast radiator tower attached at the top to multiple wires extending out radially from the mast to ground, like a tent or umbrella, insulated at the ends. Extremely narrow bandwidth, requires large loading coil and low resistance counterpoise ground. Used for long range military communications.


The most widely-used class of antenna, a dipole antenna consists of two symmetrical radiators such as metal rods or wires, with one side of the balanced feedline from the transmitter or receiver attached to each.[18][21] A horizontal dipole radiates in two lobes perpendicular to the antenna's axis. A half-wave dipole the most common type, has two collinear elements each a quarter wavelength long and a gain of 2.15 dBi. Used individually as low gain antennas, dipoles are also used as driven elements in many more complicated higher gain types of antennas.

  • Yagi-Uda - One of the most common directional antennas at HF, VHF, and UHF frequencies. Consists of multiple half wave dipole elements in a line, with a single driven element and multiple parasitic elements which serve to focus the radio waves in a beam. It radiates a unidirectional beam with gain up to about 17 dBi depending on the number of elements used, and has a narrow bandwidth of a few percent. Used for rooftop television antennas, point-to-point communication links, and long distance shortwave communication using skywave ("skip") reflection from the ionosphere.
  • Log periodic - Unique in that it is a high gain dipole antenna with broad bandwidth. It consists of many dipole driven elements in a line, with alternating polarization and gradually increasing width. Used for rooftop television antennas.
  • Turnstile - Two dipole antennas mounted at right angles, fed with a phase difference of 90°. This can radiate horizontally polarized radio waves broadside in an omnidirectional pattern, and circularly polarized radio waves off the end. Used for receiving signals from satellites, as circular polarization is used for satellite communication since it is not sensitive to the orientation of the satellite's antenna.
  • Corner reflector - A directive antenna with moderate gain of 15 - 20 dBi 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.
  • 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 used in arrays.


Array antennas consist of multiple antennas working as a single antenna. Typically they consist of arrays of identical driven elements, usually dipoles fed in phase, giving increased gain over that of a single dipole.[18][22][23]

  • Collinear - Consist of a number of dipoles in a vertical line. It is a high gain omnidirectional antenna, meaning more of the power is radiated in horizontal directions and less into the sky or ground and wasted. Gain of 8 to 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.
  • 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 - 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 - Large directional wire transmitting antenna used at HF by shortwave broadcasting stations. It consists of a vertical rectangular array of wire dipoles suspended in front of a flat reflector screen consisting of a vertical "curtain" of parallel 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
  • Batwing or superturnstile - A specialized antenna used in television broadcasting consisting of perpendicular pairs of dipoles with radiators resembling bat wings. Multiple batwing antennas are stacked vertically on a mast to make VHF television broadcast antennas. Omnidirectional radiation pattern with high gain in horizontal directions. The batwing shape gives them wide bandwidth.
  • microstrip - an array of patch antennas on a substrate fed by microstrip feedlines. Microwave antenna that can achieve large gains in compact space. Ease of fabrication by PCB techniques have made them popular in modern wireless devices. Beamwidth and polarization can be actively reconfigurable.


Ferrite rod receiving antenna from AM radio, 550 - 1600 KHz. The antenna also serves as the inductor in the tuned circuit for the receiver.

Loop antennas consist of a loop or coil of wire.[18][24][25] Loops with circumference of a wavelength or larger act similarly to dipole antennas. However loops small in comparison to a wavelength act differently. They interact with the magnetic field of the radio wave instead of the electric field as other antennas do, and so are relatively insensitive to nearby electrical noise. However they have low radiation resistance, and so are inefficient for transmitting. They are used as receiving antennas at low frequencies, and also as direction finding antennas.

  • Ferrite (loopstick) - Used as the receiving antenna in virtually all AM radios at MF, LF, and VLF frequencies. A coil of wire wrapped around a ferrite magnetic core. The magnetic core concentrates the magnetic field, enabling this small compact antenna to receive radio waves many times its size. Has two main lobes off the ends of the ferrite stick.


Aperture antennas are the main type of directional antennas used at microwave frequencies and above.[18][26] They consist of a small dipole or loop feed antenna inside a three-dimensional guiding structure large compared to a wavelength, with an aperture to emit the radio waves. Since the antenna structure itself is nonresonant they can be used over a wide frequency range by replacing or tuning the feed antenna.

  • 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 - Simple antenna with moderate gains of 15 to 25 dBi consists of a flaring metal horn attached to a waveguide. Used for applications such as radar guns, radiometers and as feed antennas for parabolic dishes.
  • Slot - Consist 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.
  • Dielectric resonator - consists of small ball or puck-shaped piece of dielectric material excited by aperture in waveguide Used at millimeter wave frequencies

Traveling wave

Unlike the above antennas, traveling wave antennas are nonresonant so they have inherently broad bandwidth.[18][27] They are typically wire antennas multiple wavelengths long, through which the voltage and current waves travel in one direction, instead of bouncing back and forth to form standing waves as in resonant antennas. They have linear polarization (except for the helical antenna). Unidirectional traveling wave antennas are terminated by a resistor at one end equal to the antenna's characteristic resistance, to absorb the waves from one direction. This makes them inefficient as transmitting antennas.

  • Random wire - This describes the typical antenna used to receive shortwave radio, consisting of a random length of wire either strung outdoors between supports or indoors in a zigzag pattern along walls, connected to the receiver at one end. Can have complex radiation patterns with several lobes at angles to the wire.
  • Beverage - Simplest unidirectional traveling wave antenna. Consists of a straight wire one to several wavelengths long, suspended near the ground, connected to the receiver at one end and terminated by a resistor equal to its characteristic impedance, 400 to 800Ω at the other end. It's radiation pattern has a main lobe at a shallow angle in the sky off the terminated end. It is used for reception of skywaves reflected off the ionosphere in long distance "skip" shortwave communication.
  • Rhombic - Consists of four equal wire sections shaped like a rhombus. It is fed by a balanced feedline at one of the acute corners, and the two sides are connected to a resistor equal to the characteristic resistance of the antenna at the other. It has a main lobe in a horizontal direction off the terminated end of the rhombus. Used for skywave communication on shortwave bands.
  • Helical (axial mode) - Consists of a wire in the shape of a helix mounted above a reflecting screen. It radiates circularly polarized waves in a beam off the end, with a typical gain of 15 dBi. It is used at VHF and UHF frequencies for communication with satellites and animal tracking transmitters, which use circular polarization because it is insensitive to the relative orientation of the antennas.
  • Leaky wave - Microwave antennas consisting of a waveguide or coaxial cable with a slot or apertures cut in it so it radiates continuously along its length.

Effect of ground

Ground reflections is one of the common types of multipath.[28][29][30]



For very low frequencies to high frequencies (<30 MHz), the ground behaves as a lossy dielectric, [31] Thus the ground is characterized both by a conductivity [32] and permittivity (dielectric constant) which can be measured for a given soil (but is influenced by fluctuating moisture levels) or can be estimated from certain maps. At lower frequencies the ground acts mainly as a good conductor, which AM middle wave broadcast (.5 - 1.6 MHz) antennas depend on.


On the other hand, vertically polarized radiation is not well reflected by the ground except at grazing incidence or over very highly conducting surfaces such as sea water. [33] However the grazing angle reflection important for ground wave propagation, using vertical polarization, is in phase with the direct wave, providing a boost of up to 6 db, as is detailed below.



The net quality of a ground reflection depends on the topography of the surface. When the irregularities of the surface are much smaller than the wavelength, we are in the regime of specular reflection, and the receiver sees both the real antenna and an image of the antenna under the ground due to reflection. But if the ground has irregularities not small compared to the wavelength, reflections will not be coherent but shifted by random phases. With shorter wavelengths (higher frequencies), this is generally the case.







\textstyle{\left|E_V\right|=2\left|E_0\right| \, \left|\cos\left({2 \pi h\over\lambda}\sin\theta\right) \right|}


\textstyle{\left|E_H\right|=2\left|E_0\right| \, \left|\sin\left({2 \pi h\over\lambda}\sin\theta\right) \right|}


  • \scriptstyle{E_0} is the electrical field that would be received by the direct wave if there were no ground.
  • θ is the elevation angle of the wave being considered.
  • \scriptstyle{\lambda} is the wavelength.
  • \scriptstyle{h} is the height of the antenna (half the distance between the antenna and its image).



On the other hand, classical (analog) television transmissions are usually horizontally polarized, because in urban areas buildings can reflect the electromagnetic waves and create ghost images due to multipath propagation. Using horizontal polarization, ghosting is reduced because the amount of reflection of electromagnetic waves in the p polarization (horizontal polarization off the side of a building) is generally less than s (vertical, in this case) polarization. Vertically polarized analog television has nevertheless been used in some rural areas. In digital terrestrial television such reflections are less problematic, due to robustness of binary transmissions and error correction.

Mutual impedance and interaction between antennas

Current circulating in one antenna generally induces a voltage across the feedpoint of nearby antennas or antenna elements. The mathematics presented below are useful in analyzing the electrical behaviour of antenna arrays, where the properties of the individual array elements (such as half wave dipoles) are already known. If those elements were widely separated and driven in a certain amplitude and phase, then each would act independently as that element is known to. However, because of the mutual interaction between their electric and magnetic fields due to proximity, the currents in each element are not simply a function of the applied voltage (according to its driving point impedance), but depend on the currents in the other nearby elements. Note that this now is a near field phenomenon which could not be properly accounted for using the Friis transmission equation for instance.

The elements' feedpoint currents and voltages can be related to each other using the concept of mutual impedance \scriptstyle{Z_{ji}} between every pair of antennas just as the mutual impedance \scriptstyle{j\omega M} describes the voltage induced in one inductor by a current through a nearby coil coupled to it through a mutual inductance M. The mutual impedance \scriptstyle{Z_{21}} between two antennas is defined[34] as:

Z_{ji}={v_j\over i_i}

where \textstyle{i_{i}} is the current flowing in antenna i and \textstyle{v_j} is the voltage induced at the open-circuited feedpoint of antenna j due to \textstyle{i_{1}} when all other currents ik are zero. The mutual impendances can be viewed as the elements of a symmetric square impedance matrix Z. Note that the diagonal elements, Z_{ii}={v_i\over i_i}, are simply the driving point impedances of each element.

Using this definition, the voltages present at the feedpoints of a set of coupled antennas can be expressed as the multiplication of the impedance matrix times the vector of currents. Written out as discrete equations, that means:

\begin{matrix} v_1&=&i_1Z_{11}&+&i_2Z_{12}&+& \cdots &+& i_nZ_{1n}\\ v_2&=&i_1Z_{21}&+& i_2Z_{22}&+&\cdots&+&i_nZ_{2n} \\ \vdots & & \vdots & & \vdots & & & & \vdots \\ v_n&=&i_1Z_{n1}&+&i_2Z_{n2}&+&\cdots&+&i_nZ_{nn}\end{matrix}


  • \scriptstyle{v_i} is the voltage at the terminals of antenna i
  • \scriptstyle{i_i} is the current flowing between the terminals of antenna i
  • \scriptstyle{Z_{ii}} is the driving point impedance of antenna i
Mutual impedance between parallel \scriptstyle dipoles not staggered. Curves Re and Im are the resistive and reactive parts of the impedance.

As is the case for mutual inductances,


This is a consequence of Lorentz reciprocity. For an antenna element i not connected to anything (open circuited) one can write i_i=0. But for an element i which is short circuited, a current is generated across that short but no voltage is allowed, so the corresponding \textstyle{v_i}=0. This is the case, for instance, with the so-called parasitic elements of a Yagi-Uda antenna where the solid rod can be viewed as a dipole antenna shorted across its feedpoint. Parasitic elements are unpowered elements that absorb and reradiate RF energy according to the induced current calculated using such a system of equations.



Antennas and supporting structures

Diagrams as part of a system

See also


  2. ^ In the context of electrical engineering and physics, the plural of antenna is antennas, and it has been this way since about 1950 (or earlier), when a cornerstone textbook in this field, Antennas, was published by the physicist and electrical engineer John D. Kraus of The Ohio State University. Besides in the title, Dr. Kraus noted this in a footnote on the first page of his book. Insects may have "antennae", but this form is not used in the context of electronics or physics.
  3. ^ For example
  4. ^ "IEEE Transactions on Antennas and Propagation". 
  5. ^ Marconi, "Wireless Telegraphic Communication: Nobel Lecture, 11 December 1909." Nobel Lectures. Physics 1901–1921. Amsterdam: Elsevier Publishing Company, 1967: 196–222. p. 206.
  6. ^ "The Nobel Prize in Physics 1909". 
  7. ^  
  8. ^  
  9. ^  
  10. ^ Schantz, Hans Gregory (2003), "Introduction to ultra-wideband antennas" (PDF), Proceedings of the 2003 IEEE UWBST Conference. 
  11. ^ "Media Advisory: Apply Now to Attend the ALMA Observatory Inauguration". ESO Announcement. Retrieved 4 December 2012. 
  15. ^ This example assumes a length to diameter ratio of 1000.
  16. ^ Impedance is caused by the same physics as refractive index in optics, although impedance effects are typically one-dimensional, where effects of refractive index is three-dimensional.
  17. ^ Bevelaqua, Peter J. "Types of Antennas". Antenna Theory. Peter Bevelaqua's private website. Retrieved June 28, 2015. 
  18. ^ a b c d e f g Aksoy, Serkan (2008). "Antennas" (PDF). Lecture Notes-v.1.3.4. Electrical Engineering Dept., Gebze Technical University, Gebze, Turkey. Retrieved June 29, 2015. 
  19. ^ Balanis, Constantine A. (2005). Antenna Theory: Analysis and Design, 3rd Ed., Vol. 1. John Wiley and Sons. p. 4.  
  20. ^ , Antenna-Theory.comMonopole AntennaBevelaqua,
  21. ^ , Antenna-Theory.comDipole AntennaBevelaqua,
  22. ^ , Antenna-Theory.comAntenna ArraysBevelaqua,
  23. ^ , p. 283-371Antenna Theory, Vol. 1Balanis,
  24. ^ , Antenna-Theory.comLoop AntennasBevelaqua,
  25. ^ , p. 231-275Antenna Theory, Vol. 1Balanis,
  26. ^ , p. 653-728Antenna Theory, Vol. 1Balanis,
  27. ^ , p. 549-602Antenna Theory, Vol. 1Balanis,
  28. ^ Fixed Broadband Wireless System Design, p. 130, at Google Books
  29. ^ Monopole Antennas, p. 340, at Google Books
  30. ^ Wireless and Mobile Communication, p. 37, at Google Books
  31. ^ H. Ward Silver, ed. (2011). ARRL Antenna Book, p. 3-2. Newington, Connecticut: American Radio Relay League. ISBN 978-0-87259-694-8
  32. ^
  33. ^ H. Ward Silver, ed. (2011). ARRL Antenna Book, p. 3-23. Newington, Connecticut: American Radio Relay League. ISBN 978-0-87259-694-8
  34. ^ Kai Fong Lee (1984). Principles of Antenna Theory. John Wiley and Sons Ltd.  


General references

  • Antennas (4th edition), by J. Kraus and R. Marhefka, McGraw-Hill, 2001, ISBN 0-07-232103-2;
  • Antennenbuch, by Karl Rothammel, publ. Franck'sche Verlagshandlung Stuttgart, 1991, ISBN 3-440-05853-0; other editions (in German)

"Practical antenna" references

  • antenna-theory.comAntenna Theory
  • Antenna typesAntennas
  • EM TalkPatch Antenna: From Simulation to Realization
  • , Stuart G. Downs, WY6EEWhy Antennas Radiate (PDF)
  • , Ron Schmitt, EDN Magazine, March 2 2000Understanding electromagnetic fields and antenna radiation takes (almost) no math (PDF)

Theory and simulations

  • "[2]" Formulas for simulating and optimizing Antenna specs and placement
  • "Support > Knowledgebase > RF Basics > Antennas / Cables > dBi vs. dBd detail". MaxStream, Inc., 2005. (ed. How to measure antenna gain) (New location: Note: to skip the registration form click the link below it)
  • Yagis and Log Periodics, Astrosurf article.
  • Tests of FM/VHF receiving antennas.
Effect of ground references

Patents and USPTO

  • CLASS 343, Communication: Radio Wave Antenna

Further reading


The dictionary definition of antenna at Wiktionary

