- For other uses, see Antenna.
An antenna or aerial is an electrical antena device designed to transmit or receive radio waves or, more generally, any electromagnetic waves. Antennas are antenne used in systems such as radio and television broadcasting, point-to-point radio antnna communication, radar, and space exploration. Antennas usually antennna work in air or outer space, but can also be operated under water or even through anntenna soil and rock at certain frequencies.
Physically, an antenna is an arrangement of tv antenna conductors that generate a radiating electromagnetic field in response to an applied antenna alternating voltage and the associated alternating electric current, or can cell phone antenna be placed in an electromagnetic field so that the field will hdtv antenna induce an alternating current in the antenna and tv antennas a voltage between its terminals. Some antenna devices (parabola, horn antenna) just adapt the free space to another type of antenna.
Antennas were wifi antenna antenna antennas used for the first time, in 1889, by Heinrich Hertz (1857-1894) to prove the existence of electromagnetic waves antenna towers predicted by the theory of James Clerk Maxwell. He even placed the cb antenna emitter dipole in the focal point of a parabolic reflector. He published his work and installation drawings in antennas Annalen der wireless antenna Physik und Chemie (vol. 36, 1889).
- 1 Terminology
- 2 Overview
- 3 Antenna antenna balls parameters
- 3.1 Resonant frequency
- 3.2 Gain
- 3.3 Bandwidth
- 3.4 Impedance
- 3.5 Radiation antenna toppers radio antenna towers pattern
- 3.6 Polarization
- 3.7 Efficiency
- 3.8 Overview television antennas of antenna parameters
- 3.9 Transmission fm antenna and reception
- 4 Basic antenna screwdriver antenna models
- 5 Antennas in reception
- 6 Physical background
- 7 Effect gps antenna of ground
- 8 Mutual diamond antenna impedance and interaction between antennas
- 9 See also
- 10 External antenna tower articles and further reading
The words car antenna "antenna" (plural: antennas ) and "aerial" are used interchangeably throughout this article. The cell phone antenna booster origin of the word antenna relative antenna tower specifications to wireless apparatus is attributed to Guglielmo Marconi. In 1895, while testing early radio apparatus in the outdoor antenna installation wiring Swiss Alps at Salvan, Switzerland in the Mont antenna mobile satellite tv Blanc region, Marconi experimented with early wireless equipment. A 2.5 meter long pole, along which was carried a antenna tower repair wire, was used as a radiating and receiving aerial satellite antenna element. In Italian a tent pole is television antenna known as l'antenna centrale, and the pole with a wire alongside it used antenna mast as an aerial was simply called l'antenna. Until then wireless radiating transmitting antennas amateur radio and receiving elements were known simply as aerials or terminals. Marconi's use of the word antenna (Italian for pole) would ham radio antenna towers become a popular term for what today is uniformly known as the "antenna". 
A "hertz antenna" is a set of terminals that build radio antenna tower does not require the presence hdtv antennas of a ground for its operation. A "loaded antenna" is an yagi antenna active antenna having an elongated portion of appreciable electrical length and having additional inductance or capacitance directly in series or best hdtv antenna shunt with the elongated portion hd antenna so as to modify the standing wave pattern existing along the portion or to change the effective wireless internet antenna wireless internet antenna electrical length of the portion. An "antenna grounding discone antenna structure" is a ground for establishing a reference potential level for wilson antenna operating the active antenna. It can be any structure closely associated with (or acting as) the ground which is wireless internet antenna connected to the terminal of the signal receiver or source opposing the active antenna satellite tv antenna terminal, (i.e., satellite tv antenna dish the signal receiver or source is interposed between the active antenna and this structure).
There are two fundamental types of antennas, which, with reference to a specific three hd tv antenna dimensional (usually horizontal or vertical) plane are:
- either omni-directional (radiate equally in the plane)
- directional (radiates more windom antenna in one direction than in the other).
All antennas radiate j pole antenna (or emanate) some energy in all antenna dish network satellite directions in free space but careful construction results in large directivity in certain directions and negligible energy radiated in other directions.
By adding antenna hdtv samsung additional live streaming video antenna conducting rods or coils (called elements) and varying their length, spacing, and orientation (or changing the direction of the antenna beam), an antenna with wifi antennas specific desired properties antenna design can be created, such as a Yagi-Uda Antenna (often abbreviated to "Yagi"). An "antenna array" is a plurality best indoor tv antenna of active antennas coupled antenna booster to a common source or load to produce a directive radiation pattern. Usually the spatial relationship also contributes to the directivity oferta antenna satellite dish network of the antenna. By the use of term "active element" it is intended to cb antennas describe an element whose energy output is modified due to the rca hdtv antenna presence of a source of tv antenna review energy in the element (other than the mere antenna rotor signal energy which passes through the circuit) or an element in which the ham radio antenna energy output from a source of energy is controlled by the signal input. The "antenna lead-in" is hdtv indoor antenna the conductive means (as for example a transmission line or feed line) for conveying the signal energy marine tv antenna between the beverage antenna active antenna and the signal source. It extends directly from the active antenna towards 4050 lg cell phone antenna replacement the source. The "antenna feed" refers to the components between antenna dish network oferta satellite the active antenna and an amplifier. The "antenna counterpoise" is the structure of conductive antenna marine satellite tv material most closely associated with ground but insulated from (or indoor tv antenna capacitively coupled to) the natural ground. It aids in the function of the natural ground, particularly outdoor hdtv antenna where variations (or limitations) of the characteristics of the natural ground interfere with its proper function. Such structure samsung amplified indoor hdtv antenna are usually connected to the terk hdtv antenna terminal of the signal receiver or source opposing the active antenna terminal.
A "antenna component" is a portion db4 hdtv antenna of the antenna performing a distinct function and limited for use in motorola cell phone antenna an antenna, as for example, a outdoor tv antenna reflector, director, or active antenna. "Parasitic elements" are usually metallic conductive structures which reradiate into free space impinging electromagnetic radiation philips hdtv antenna coming samsung hdtv antenna from or going to the active antenna. The "electromagnetic wave refractor" is a structure which is shaped or positioned to delay or accelerate am antenna transmitted electromagnetic waves, passing through such structure, an amount antenna dish multi satellite which varies over the wave front. The refractor alters the direction high definition antenna of propagation of the waves high definition television antenna emitted from the structure with respect to the waves impinging on the structure. It can alternatively bring the indoor hdtv antenna wave to a focus or alter the wave front in other ways, such as low profile uhf antenna to convert a spherical wave front to a planar wave front (or vice versa). The velocity outbacker antenna of the wave radiated have a component which is in am radio antenna the same direction ("director") or in cell phone antenna adapter the opposite direction ("reflector") that of the velocity diamond antennas of the impinging wave. A "director" is usually a metallic conductive structure which reradiates into free space impinging electromagnetic radiation scanner antenna coming from or going to the active antenna, 6 meter antennas the velocity of the reradiated wave having a component in the direction of velocity of the impinging wave. The director uhf hdtv antenna modifies the radiation pattern of the active antenna and there is no antenna car satellite significant potential relationship between the cellular antenna active antenna and this conductive structure. A hdtv antenna new "reflector" is usually a metallic conductive structure (e.g., screen, rod or plate) which reradiates back into free space low profile antenna impinging electromagnetic radiation coming from or going to the active outdoor television antenna antenna. The velocity of the returned wave having a am antennas component in a direction opposite to the direction of velocity of the impinging wave. The reflector modifies the radiation of the hf antenna active antenna. There is no significant potential relationship microwave antenna between the active antenna and this conductive structure.
An "antenna coupling network" is mobile satellite antenna a passive network (which may be any combination of a resistive, inductive or capacitive circuit(s)) for transmitting mobile tv antenna the signal energy between the active antenna and a source (or receiver) radio antenna of such signal energy. radio shack hdtv antenna Typically, antennas are designed to operate in a relatively narrow frequency range. usb gps antenna The design criteria for receiving and transmitting antennas differ slightly, but generally an antenna can receive and marine satellite tv antenna transmit equally well. This property is called "reciprocity".
The vast majority of antennas are simple vertical rods pda gps antenna a quarter of a wavelength long. xm antenna Such antennas are simple in construction, usually inexpensive, and both radiate in antenna theory and receive from all horizontal directions cb radio antennas (omnidirectional). One limitation of this antenna is that it does not radiate or receive in the direction power antenna in which the rod points. This region is wireless cell phone antenna called the antenna blind cone or null. Antennas have practical use for the transmission and reception of radio frequency car mobile tv antenna signals (radio, TV, etc.), which can theroretically travel over car radio antenna great distances at the speed of light (the true velocity depends on the transmission medium external cell phone antenna over which it passes). These signals can hdtv antenna review also pass through nonconducting walls (although often there is a variable signal reduction loop antenna depending on the type of wall, and natural rock can be very reflective portable satellite antenna to radio signals).
There are several critical parameters that affect an antenna's performance antenna boat satellite tv and can be adjusted during the design process. These asus wifi wireless lan card w2f antenna are resonant frequency, impedance, gain, aperture or ham antennas radiation pattern, polarization, efficiency and bandwidth. Transmit antennas may also have a usb wireless antenna maximum power rating, and receive antennas differ in their noise rejection properties.
The "resonant frequency" and winegard high definition television antenna "electrical resonance" is related to the antenna satellite dish electrical length of the antenna. The electrical length is usually the physical length of the wire multiplied by car antenna topper the ratio of the speed of wave propagation in the wire. comet antenna Typically an antenna is tuned for a specific frequency, and is effective for digital antenna a range of frequencies usually centered on that resonant frequency. However, the other properties of the mobile ham antenna antenna (especially radiation pattern and impedance) change with frequency, picking a hdtv antenna so the antenna's resonant frequency may merely be sirius antenna close to the center frequency of these other more important properties.
Antennas can vhf antenna be made resonant on harmonic frequencies with lengths that are fractions of the target wavelength. Some antenna designs have multiple resonant antenna wire frequencies, best outdoor tv antenna and some are relatively effective over a very broad range of frequencies. The digital tv antenna most commonly known type of wide band aerial is the logarithmic or log flashing antennas periodic, but its gain is usually much lower than that of a specific or scanner antennas narrower band aerial.
"Gain" as a parameter measures the directionality of a given antenna. An antenna tv antenna booster with a low gain emits digital antenna dual band wireless radiation in all directions equally, whereas a high-gain antenna will preferentially radiate in particular directions. Specifically, the Gain, Directive gain or terk antenna Power gain of an antenna cellular motorola phone antenna is defined as the ratio of the intensity (power per car diversity tv antenna unit surface) radiated by the antenna in a given direction at an arbitrary dish antenna distance divided by the intensity radiated at the same distance by an hypothetical mobile tv antennas isotropic antenna:
We write "hypothetical" because a perfect isotropic antenna cannot exist in reality (the electric and magnetic field would nvis antennas not satisfy Maxwell equations for electromagnetic fields). Gain is philips hdtv antenna instructions a dimensionless number (without satellite radio antenna units).
The gain of an antenna is a passive phenomena - power is not wilson antennas added by the antenna, but simply redistributed to provide more radiated antenna array phased satellite tv power in a certain direction than would be transmitted by an isotropic antenna. If an antenna has antenna mounting hardware a greater than one gain in some directions, it must have a less than one gain in cellphone antennas other directions since energy is conserved by the comet antennas antenna. An antenna designer must take into account the application for the satellite dish antenna antenna when determining the gain. High-gain antennas have the advantage of longer range and better signal antenna amplifier quality, but must be aimed carefully in a particular direction. Low-gain antennas have antenna portable satellite shorter range, but the orientation of the antenna art bell antenna is inconsequential. For example, a dish antenna on a auto hidden antenna spacecraft is a high-gain device (must be pointed at the planet butternut antenna to be effective), while a typical WiFi antenna in cell phone booster antenna a laptop computer is low-gain (as long as the base station is within cellphone plan comparison cell phone antenna cellp range, the antenna can be in an any orientation in space).
As an example, consider an antenna that radiates an electromagnetic wave whose dipole fm antennas electrical field has an amplitude extending cell phone reach antenna verizon wireless at a distance . This amplitude is given by:
- is the current microwave antennas fed to the antenna and
- is a constant characteristic of each antenna.
For a large distance . The radiated satellite antenna alignment wave can be considered locally as a wireless router antenna plane wave. The intensity of an electromagnetic plane wave is:
where is an antenna dish satellite tv universal constant called vacuum impedance. and
If the antenna satellite tv xxasdf resistive part of the series impedance of the antenna is , the power fed to the antenna is . The intensity automobile radio antennas of an isotropic antenna is the hdtv antenna guide power so fed divided by the surface of the sphere of radius network time server hardware antenna :
The directive gain is:
If the antenna is a half wave dipole and . The gain is predator antenna .
Often the gain is given in dBi (decibels over isotropic radiator):
The dBi are antenna atlanta dish satellite just decibels with an i added to remind that the antenna direction tv reference gain is that antenna flat satellite of an isotropic antenna.
One of the simplest antennas, the short dipole has a antenna mounts gain of . Sometimes, the short dipole is taken as reference, instead the isotropic radiator. The gain is antenna radio satellite sirius then given in dBd (decibels over short dipole):
- dBd = dBi – 1.76
The "bandwidth" of cell phone external antenna an antenna is the notebook wireless antenna range of frequencies over which it is effective, usually centered around the resonant frequency. The bandwidth of an antenna r v satellite antenna satellite tv dish antenna may be increased by several techniques, including using thicker wires, replacing wires with cages to simulate a thicker wire, tapering antenna components (like in wireless card antenna a feed horn), and combining multiple antennas into a single wireless lan antenna assembly and allowing the natural impedance to select the amateur radio antenna correct antenna. Small antennas are usually preferred for convenience, but there antenna free satellite tv is a fundamental limit relating bandwidth, size and efficiency.
"Impedance" is analogous to refractive antenna i730 nextel index in optics. As the electric wave travels through the antenna phone satellite different parts of the antenna system (radio, antennae feed line, antenna, free space) it may encounter differences in impedance. cb radio antenna At each interface, depending on the impedance match, some fraction of the wave's energy will reflect back to the source, forming a cell phone antenna boosters standing wave in the cell phone antennas cell phone antennas feed line. The ratio of maximum power to minimum power in the wave homemade am antenna can be measured and is called the standing wave ratio (SWR). A SWR of 1:1 is ideal. A SWR smart antenna of 1.5:1 is considered to be marginally acceptable in low used u.s military vehicle antenna set with base power applications where power loss is more critical, although an SWR as high winegard antennas as 6:1 may still be usable with the right equipment. Minimizing impedance differences xm marine antenna at each interface (impedance amplified hdtv antenna matching) will reduce SWR and maximize power transfer through each part of the antenna system.
Complex impedance antenna building of an antenna is related to antenna specialists the electrical length of the antenna at the wavelength in use. The impedance of fm antennas an antenna can be matched to the feed line larsen antennas and radio by adjusting the impedance of the feed line, using the feed line as an impedance transformer. More commonly, motorola l series super flashing light antenna the impedance is adjusted at network time server antenna the load (see below) with an antenna tuner, a balun, a matching transformer, matching networks composed of inductors and capacitors, or matching satellite dish antenna xxasdf sections such as the gamma match.
The radiation pattern is a graphical depiction of the 1 antenna mp portable sold worldwide relative field strength transmitted from or received by the antenna. antenna for wireless notebook As antennas radiate in space often several curves are necessary to describe antenna satellite used the antenna. If the radiation of the antenna is symmetrical about an axis cb antenna mount (as is the case in dipole, helical and some parabolic antennas) a unique graph is sufficient.
Each antenna home made tv antennas supplier/user has different standards as well larsen antenna as plotting formats. Each format has its own pluses and minuses.
Radiation pattern of an linksys wireless usb network adapter external antenna antenna can be defined as the locus of all points where the emitted power parabolic antenna per unit surface is the same. random wire antenna As the radiated power per unit surface is proportional to the squared electrical field of the electromagnetic wave. The radiation pattern is the locus telescoping antenna masts vw cabriolet radio antenna of points with the same electrical field. In this representation, the reference is, usually, the best angle of emission.
It is also wireless network antenna possible to depict the directive gain of the antenna 80211b wireless lan card antenna as a function of the direction. Often the airstation 54mbps wireless notebook adapter with antenna gain is given in decibels. In this case, it is not possible to draw low values of gain.
The graphs can be antenna channel dish master satellite drawn using cartesian (rectangular) coordinates or antenna chicago dish satellite a polar plot.
The shape of curves can be very different in cartesian or antenna ham radio satellite polar coordinates and with the choice of the antenna rv satellite tv limits of the logarithmic scale. The four drawings below are the radiation patterns antenna satellite system television of a same half-wave antenna
Radiation pattern antenna tower collapse of a half-wave dipole antenna. Linear scale.
Gain broadband wireless internet antenna of a half-wave dipole. The scale is in dBi.
Gain car radio antennas of a half-wave dipole. Cartesian representation.
3D Radiation pattern of a half-wave coaxial colinear antenna dipole antenna.
The "polarization" of an antenna is the orientation of the ham antenna electric field (E-plane) of the radio wave with homemade antenna mast respect to the Earth's surface and is determined by the physical structure of the antenna and by its homemade scanner antenna orientation. It has nothing in common with antenna directionality terms: how to setup home dish antenna "horizontal", "vertical" and "circular". Thus, a simple straight wire antenna will have one polarization when mounted vertically, multi satellite dish antenna and a different polarization when mounted horizontally. "Electromagnetic wave polarization scanner antenna booster filters" are structures which can be employed slinky antenna to act directly on the electromagnetic wave to filter out wave energy wireless antenna for portable tv of an undesired polarization and to pass wave wireless card external antenna jack laptop orinoco energy of a desired polarization.
Reflections generally affect polarization. For radio waves the most important reflector is the ionosphere - wireless router bridge network external antenna dsl modem signals which reflect from it will have their polarization changed unpredictably. For wireless tv antenna signals which are reflected by the ionosphere, polarization cannot wireless usb adapter external antenna be relied upon. For line-of-sight communications for which polarization 2 meter antennas can be relied upon, it can make a large difference in signal quality to have the transmitter and receiver using acdma cell phone antenna diy the same polarization; many tens of dB difference are commonly seen antenna buddipole buddistick dipole hf portable vertical and this is more than enough to make the difference between reasonable antenna cell e105 phone samsung communication and a broken link.
Polarization is largely predictable from antenna construction, but especially antenna guy cell phone antennas in directional antennas, the polarization of side lobes can be arrow antenna quite different from that of the main propagation lobe. For radio antennas, polarization asus wifi b wireless lan card w2f antenna corresponds to the orientation of the radiating element in an ham radio antennas antenna. A vertical omnidirectional WiFi antenna internal cell phone antenna will have vertical polarization (the most common type). An exception is a class of elongated waveguide antennas in which vertically placed antennas are rv satellite tv antenna horizontally polarized. Many commercial antennas are st-2 scanner antenna marked as to the polarization of their emitted signals.
Polarization is the sum of terk antennas the E-plane orientations over time projected onto an imaginary plane tv antenna installation perpendicular to the direction of motion of the radio wave. In the most general case, polarization tv antenna towers is elliptical (the projection is oblong), meaning that the antenna varies over time in wineguard high definition television antenna the polarization of the radio waves it is emitting. wireless lan card antenna Two special cases are linear polarization (the ellipse collapses into a line) and circular xm antennas polarization (in 100m bluetooth wireless usb adapter with antenna which the ellipse varies maximally). In linear polarization the antenna compels the electric antenna for cell phone field of the emitted radio wave to a particular orientation. Depending on the orientation of antenna noise bridge the antenna mounting, the usual linear cases are horizontal and vertical cell phone internal antenna polarization. In circular polarization, the antenna continuously varies the electric field of the radio wave through all possible values cellular antennas of its orientation with regard to the Earth's surface. Circular polarizations, like elliptical dish satellite antenna ones, are classified flagpole antenna as right-hand polarized or left-hand polarized using a "thumb in the direction of the propagation" rule. Optical hd antennas researchers use the same rule of thumb, but pointing indoor antennas for cell phones it in the direction of the emitter, not in the direction of propagation, and so are international satellite 28at29 antenna service bra opposite to radio engineers' use.
In practice, regardless of confusing terminology, it is important ku band vsat antenna that linearly polarized low noise antenna john doty antennas be matched, lest the received signal strength be greatly reduced. So horizontal should be made in usa antenna flags used with horizontal and vertical with vertical. Intermediate matchings will miata antenna install lose some signal strength, but not as much as a complete mismatch. Transmitters microwave antenna systems mounted on vehicles with large motional freedom commonly use circularly rack mount antenna polarized antennas so that there will never be a complete mismatch with signals from other sources. In the case of radar, this is s band antenna often reflections from rain drops.
"Efficiency" is the ratio of power satellite radio antenna wireless actually radiated to the power put into the antenna terminals. A dummy tv antennas for mobile use load may have a SWR of 1:1 but w5qjr antenna an efficiency of 0, as it absorbs all power and radiates heat but wilson cell phone antenna not RF energy, showing that SWR alone is not an wireless usb antenna effective measure of an antenna's efficiency. Radiation in an antenna is caused by radiation resistance antenna card network wireless which can only be measured as part of total resistance boost antenna cell phone including loss resistance. Loss resistance usually results in heat generation rather than radiation, and therefore, reduces efficiency.
Overview of cell antenna antenna parameters
Except for polarization, the SWR is the most cell phone antennas sanyo easily measured of the parameters above. Impedance can be measured with specialized equipment, as it relates to the complex SWR. Measuring cellphone antenna radiation pattern requires a cheap cell phone antenna charms sophisticated setup including significant clear space (enough to put the sensor into the antenna's far field, or an anechoic force 12 antennas chamber designed for antenna measurements), careful study of experiment geometry, g5rv antenna and specialized measurement equipment that rotates the homemade wifi antenna antenna during the measurements. The distance is the space between two points, which may be immediately juxtaposed or widely spaced.
Bandwidth depends k40 cb antenna on the overall effectiveness of the antenna, so all of these parameters magnetic loop antennas must be understood to fully characterize the millimeter-wave antennas bandwidth capabilities of an antenna. However, in practice, bandwidth is typically determined by mobile antenna satellite tv looking only at SWR, i.e., by finding the frequency range over which the SWR is mobile satellite tv antenna less than a given value. Bandwidth over which an antenna exhibits mobile scanner antenna a particular radiation pattern is motorola cellular antenna v60i also important, for in practical use the performance of an antenna at pioneer xm car antenna the extremes of an assigned frequency band is important.
Transmission and reception
All of samsung cell phone antenna these parameters are expressed in terms of a transmission antenna, but are identically applicable to a receiving antenna, due to sanyo cell phone antennas reciprocity. Impedance, service providers wireless networks antenna coverage however, is not applied in an obvious way; for impedance, the impedance at the load (where the wireless antennas power is consumed) is most critical. wireless card antenna laptops For a transmitting antenna, this is the antenna itself. For a receiving antenna, this is at wireless laptop antenna the (radio) receiver rather than at the antenna. Tuning is done by adjusting the length wireless laptop cards plus antenna of an electrically long linear antenna to alter the electrical resonance of the antenna.
Antenna tuning is done wireless network card antenna by adjusting an wireless tv antennas inductance or capacitance combined with the active antenna (but distinct and separate from the 2 meter antenna the active antenna). The inductance or capacitance provides the reactance which combines with am antenna handheld monopole portable radio short the inherent reactance of the active antenna to establish a resonance in a circuit including the active am radio antenna reviews antenna. The established resonance being at a frequency other than the natural electrical antenna efficiency resonant frequency antenna external for cell phone of the active antenna. Adjustment of the inductance or capacitance changes this resonance.
Antennas used for transmission antenna system repeater have a maximum power rating, beyond which heating, arcing or sparking may occur in the components, which may antenna usb wireless cause them to be damaged antenna web or destroyed. Raising this maximum power rating usually requires larger and heavier components, block gps signal antenna which may require larger and heavier supporting structures. This is a concern only for booster antenna for wireless lan transmitting antennas, as the power received by an antenna rarely exceeds broadside array antenna the microwatt range.
Antennas designed specifically for reception car antenna samsung x426 cell phone might be optimized for noise rejection capabilities. An "antenna shield" is a cell phone car antenna conductive or low reluctance structure (such as a wire, plate or grid) which is adapted to be placed cell plan comparison lighted cellular phone antenna all in the vicinity of an antenna to reduce, as by dissipation through a resistance or dipole antenna by dipole antenna plans conduction to ground, undesired electromagnetic radiation, or electric or magnetic fields, which are ferrite rod antenna directed toward the active antenna from an external source or which emanate from the active antenna. homemade fm broadcast antennas Other methods to optimized for noise rejection can be done by selecting a narrow bandwidth so indoor satellite antenna that noise from other frequencies is rejected, or selecting a specific radiation point dish network antenna to receive direct tv satellite pattern to reject noise from a specific direction, or by quad antennas selecting a polarization different from the noise polarization, or by selecting an antenna that favors either radio antennas the ringo ranger antenna electric or magnetic field.
For instance, an antenna to be used for reception of low frequencies (below about ten satellite dish antenna bsna5 megahertz) will be subject to both south jersey cell phone antenna leases man-made noise from motors and other machinery, and from natural sources such as lightning. Successfully rejecting these forms of tv antenna signal amplifiers noise is an important antenna feature. A small coil of wire wireless antenna booster with many turns is more able to reject such noise wireless broadband antenna than a vertical antenna. However, the vertical will radiate 4 5 meter satellite antenna much more effectively on transmit, where extraneous signals are not a concern.
Basic antenna models
There are 900mhz antenna booster many variations of antennas that have various configurations. These configurations contain space or medium accessory antenna cell phone which tends to confine the energy within specified boundaries along a active antenna predetermined path (known as "restricted space"), such as wave guides, hollow resonators, and conductive wires. Below are antenna booster cell phone boosters a few common models. More can antenna booster for nextel cell phone be found in Category:Radio frequency antenna types.
A multiband rotary directional antenna for antenna cell phone yagi amateur radio use
- The isotropic radiator is a purely theoretical antenna that antenna dish parabol satellite tv radiates equally in all directions. It is considered to be a point in space with no dimensions antenna noise bridge theory and no mass. This antenna cannot physically exist, but is useful as a theoretical antenna pedestals model for comparison with all other antennas. Most antennas' gains are measured antenna specialist with reference to an isotropic radiator, car antennas and are rated in dBi (decibels with respect to an isotropic radiator).
- The dipole car cell phone antenna antenna is simply two wires pointed in opposite directions arranged either horizontally or vertically, with one end of each cell phone accessory antenna wire connected to the radio and cell phone antenna amplifier the other end hanging free in space. Since this is the simplest practical antenna, it is also used as cell phone antenna cell phone antenna reference model for other antennas; gain with respect to cell phone antenna cellphone plan comparison cellphone plan a dipole is labeled as dBd. Generally, the cell phone antenna charms dipole is considered to be omnidirectional in the plane perpendicular to the axis of the antenna, but it has deep cell phone antenna jewelry nulls cell phone home antenna booster in the directions of the axis. Variations of the dipole include the cingular lg antennas cell phone folded dipole, the half wave antenna, the groundplane antenna, the whip, and the J-pole.
- The Yagi-Uda antenna is a directional variation double bazooka antenna of the dipole with parasitic elements added with functionality similar to fm indoor antenna adding a reflector and lenses (directors) to focus a filament lightbulb.
- Loop antennas have a continuous conducting path fm stereo antenna leading from one conductor of a two-wire transmission home cell phone antenna repeater line to the other conductor. klm antenna satellite "Symmetric" loop antennas have a plane of symmetry running along the feed and through the loop. "Planar" loop antennas lie in a single low frequency antennas plane which motorola cell phone antenna signal booster also contains the conductors of the feed. "Three-dimensional" loop antennas have wire which runs in all of the motorola v60i antenna x,y, and z directions. By definition they are outenna cell phone antenna not planar. They may, however, be symmetric about planes which contain the replacement sanyo cell phone antenna feed.
- The (large) loop antenna is similar to a dipole, rv and tv antennas except that the ends of the dipole are connected to form a circle, triangle (delta loop antenna) or square. Typically a loop is satellite tv antenna satellite tv antenna a multiple of a half or full wavelength in circumference. A shakespeare antenna circular shortwave antenna loop gets higher gain (about 10%) than the other forms of large loop antenna, as gain of this slot antenna antenna is directly proportional to the area enclosed by the loop, super scanner antenna but circles can be hard to support in a the w3kh quadrifilar helix antenna flexible wire, making squares and triangles much more popular. Large loop antennas are more immune to tv indoor antenna localized noise partly due to lack of a need for a groundplane. The large loop has wireless antenna cable its strongest signal in the plane of the loop, and nulls wireless network adapter antenna in the axis wireless phone antenna perpendicular to the plane of the loop.
- The small loop antenna, also called the magnetic loop antenna is a loop of wire (in other words, antenna audiovox cell phone both ends of the wire connect to the radio) less than antenna booster cell phone wholesale a wavelength in circumference. Typically, the circumference is less than antenna booster internal antenna booster cell phone antenna 1/10 for a receiving loop, and antenna boosters cell phone less than 1/4 for a transmitting loop. Unlike nearly all other antennas in this list, this antenna antenna boosters cell phone work detects the magnetic component of the electromagnetic wave. antenna cdma cell diy phone As such, it is less sensitive to near field electric noise when properly shielded. The antenna communication mobile received voltage can be greatly increased by bringing the loop into resonance antenna hd tv type direction with a tuning capacitor. The small loop has a maximum antenna masts output when the magnetic field is normal to the plane of the loop, and antenna notebook wireless since this field is transverse to the antenna parabolicas satellite venta direction of the wave, has a maximum in the plane of the loop. This is the same mechanism as the large loop.
- The electrically antenna satellite short antenna is an open-end wire antenna tripod far less than 1/4 wavelength in length - in other words only one end of the antenna tv reception without cable or satellite antenna is best cb antenna connected to the radio, and the other end is hanging free in space. Unlike nearly all other antennas best tv antenna in this list, this antenna detects buffalo technology wireless usb antenna only the electric field of the wave instead of the electromagnetic field - think of the free end of the build tv antenna free wire as measuring the voltage of that point in space, as opposed to measuring cell phone antenna accessories both the voltage and the magnetic cell phone antennas wilson antenna field. Its receiving aperture cannot be changed by adding lumped components, but more efficient power transfer can cellular phone antenna be achieved by impedance matching with such circuits. Electrically short antennas are typically channel master 4228 antenna used where operating wavelength direct tv satellite antenna is large and space is limited, e.g. for mobile transceivers operating at long wavelengths.
- The parabolic antenna is a special external antenna for cell phone antenna where a reflector dish is fm radio antenna used to focus the signal from a directional antenna feeder. Antennas of this type are commonly found fractal antenna as Satellite television antennas, Wi-fi / WLAN, radio astronomy, radio-links, mobile phone backhaul and military ham antenna mount luggage rack tactical radio link -antennas. They are characterized by high directionality and horizontal loop antenna gain but can only be used at UHF i730 extention antennas to microwave and higher frequencies due to dimensions getting too large at lower frequencies.
- The microstrip just wireless universal auto antenna for cell phone antenna consists of a patch of metalization on a ground plane. These are low marine satellite antenna profile, light weight antennas, most suitable mobile satellite telescopic antenna for aerospace and mobile applications. Because of their low power handling capability, these morgan antenna tuner schematic antennas can be used in low-power transmitting and receiving applications. Microstrip antennas are motorola cell phone antennas the most commonly used antennas in mobile communications, satellite links, W-LAN and so motorola cellular phone antenna on because circuit functions can be motorola v265 flashing antennas directly integrated to the microstrip antenna to form compact motorola v60i external booster cellular antenna transceivers and spatial power combiners.
- The quad antenna is an array of square loops that vary nextel i730 external antenna in size. The quad is related to the loop in exactly the same way the yagi is related to passive cell phone antenna the dipole. Typically, the quad needs fewer performance automobile antennas elements to get the same gain as a yagi. Variations of the quad include the delta loop antenna radar antenna which roof mount cb antenna uses a triangle instead of a square, requiring fewer supports for large wavelength antennas.
- The random wire antenna samsung hdtv indoor antenna is simply a very long (greater than one wavelength) wire with one end shortwave antennas connected to the radio and the other in free space, arranged in any way most convenient for the toyota power antennas space available. Folding will reduce effectiveness tv antenna reviews and make theoretical analysis extremely difficult. wireless antenna for internet access hudson wisconsin (The added length helps more than the folding typically hurts.) Typically, a wireless lan pc card with detachable antenna random wire antenna will also require an antenna tuner, as it might have a wireless modem antenna random impedance that varies nonlinearly with frequency.
- The Beverage antenna is a form of directional long-wire antenna which uses a resistive termination wireless networking antenna at one end and feed from wireless usb adapter with rsma antenna connector the other.
- The endfire helical antenna is a xm satellite antenna directional antenna suited for receiving signals that are either circular polarized or randomly polarized. These are usually used with satellites, and 802.11 antenna are frequently used for the driven element on a dish.
- The Phased array active indoor antenna antenna is a group of independently fed active elements in which the relative antenna auto cell phone phases of the antenna booster cell phone respective signals feeding the elements are varied in such a way that the effective radiation pattern antenna building materials of the array is reinforced in a desired direction and suppressed in undesired directions. In plain language, antenna cell internal phone this is a directional antenna that can be aimed without moving any parts.
- Synthetic aperture antenna cell part phone radar uses a series of observations separated in time and space to antenna cell phone wireless simulate a very large antenna. Interferometry allows antenna hardware the monitor to combine signals from several radio receivers or a single moving receiver.
- A trailing wire antenna positioner antenna is used by submarines when submerged. antenna simulation These antennas are designed to pick up antenna wireless tv transmissions in the low frequency (LF) and very low frequency (VLF) ranges.
- An evolved antenna refers to an antenna asus wifi b wireless lan card w antenna fully or substantially designed using a computer algorithm cell phone antenna emission based on Darwinian evolution.
- A dielectric resonator is a variation on the conventional antenna in cell phone antenna replacement which an insulator with a large dielectric constant is used to modify the electromagnetic field. cell phone antenna signal booster It is claimed that the dielectric contains the antenna's near cell phone boost antenna field and therefore prevents it from interfering with other cell phone high gain antenna nearby antennas or circuits, making it suitable for miniature equipment common antenna system such as mobile phones.
- A feed horn is an antenna system that handles the incoming waveform from cushcraft antenna the dish to the focal point. It usually comprises of a digital vhf antennas series of rings with decreasing radius in order to drive the signal to the directv antenna polarizer.
Antennas in reception
The gain in any given direction and the impedance at a given frequency dish network antenna are the same when easy up antenna tripod the antenna is used in transmission or in reception.
The electric external antenna cell phone field of an electromagnetic wave induces a small voltage in each small segment in all electric conductors. The induced voltage depends on the foil antenna electrical field and free satellite tv antenna the conductor length. The voltage depends also on the relative orientation of genie sim cards a cell phone antenna booster a prepaid the segment and the electrical field.
Each small voltage induce a current and these currents circulate trough a small part gps usb antenna of the antenna impedance. The result of all those currents and in glass antenna tensions is far from immediate. However, jpole antenna using the reciprocity theorem, it is possible to prove that the Thévenin equivalent circuit of a kyocera cell phone antenna receiving antenna is:
- is linksys wireless router antenna the Thévenin equivalent circuit tension.
- is military discone antenna the Thévenin equivalent circuit impedance and is the same as the antenna impedance.
- is the series resistive part of the mobile antennas antenna impedance .
- is the directive gain of the antenna (the same as in emission) mobile internet antenna in the direction of arrival of electromagnetic waves.
- is the wavelength.
- is mobile tv antennae the electrical field of the incoming electromagnetic wave.
- is motorola v265 antenna the angle of misalignment of the electrical field of the incoming wave with the antenna. multifunction antenna For a dipole antenna, the maximum nextel i730 replacement antenna induced voltage is obtained when the electrical field is parallel to the dipole. police scanner antenna If this is not the case and they are misaligned rv satellite antenna by an angle , the induced voltage will be multiplied by .
- is an universal rv tv antenna constant called vacuum impedance.
The equivalent circuit satellite antenna manufacturers and the formula at right are valid for any type of antenna. It can be as well a screwdriver antennas dipole antenna, a magnetic tripod base antennas loop, a parabolic antenna, or an antenna array.
From this formula, it is easy to prove the following definitions:
- Antenna effective length
is the length tv antenna amplifier which, multiplied by the usb wireless external antenna adapter electrical field of the received wave, give the voltage of the Thévenin equivalent vlf antenna antenna circuit.
- Maximum available power
is the maximum power that an antenna can extract from the incoming electromagnetic wave.
- Cross section or effective capture website sells titanium cell phone antennas in california surface
is the surface which multiplied by the power wi-fi antenna per unit surface of the incoming wave, gives the maximum available wilson cb antenna power.
The maximum power that an antenna can extract from the wimax antenna electromagnetic field depends only on the gain of the antenna and the squared wireless antenna notebook wavelength . It does not depend on the antenna dimensions.
The xm satellite radio antenna measured electrical field was radiated seconds 2000 vw jetta antenna mast earlier.
The electrical field created by an electric charge is
- is accessory antenna cell cellular phone replacement the speed of light in vacuum.
- is the permittivity alltel motorola cellular phone antenna of free space.
- is the distance from the observation point (the place where is evaluated) to the point antenna acu where the charge was seconds antenna booster cell motorola phone before the time when the measure is done.
- is the unit vector directed from the observation point (the place where antenna boster cell phone antenna dispersion simulation software is evaluated) to the point where the charge was seconds before the time when the measure is done.
The "prime" in this formula antenna for 93 honda accord appears because the electromagnetic signal travels antenna linksys router wireless at the speed of light. Signals are observed antenna motorola replacement v60i as coming from the point where they were emitted and not from the point where the emitter is antenna rotor wire at the time of observation. The stars that we arrl antenna satellite tv dish see in the sky are no longer where we auto vs manual satellite tv antenna for rvs see them. We will see their current position years in the future; some of the build satellite mobile antenna stars that we see today no longer exist.
The first term in cb base antenna the formula is just the electrostatic field with retarded time.
The second term is as though nature cell phone antenna designs were trying to allow for the fact that the effect is retarded (Feynman).
The third term is cell phone antenna gain comparison the only term that accounts for the far field of cell phone antenna home antennas.
The two first terms are cell phone antenna lg proportional to . Only the third is proportional to .
Near the cowgirl antenna toppers antenna, all the terms are important. However, if the distance is large enough, the two first diamond d130 discone antenna terms become negligible and only the third remains:
Electrical field radiated by an element of current. The element of current, the electrical field vector and are on the same plane.
If the charge q is in sinusoidal motion with amplitude and pulsation the power radiated by the charge is:
Note that the radiated power is proportional to the fourth power of the frequency. It is far easier to radiate at high frequencies than at low frequencies. If the motion of charges is due to currents, it can be shown that the (small) electrical field radiated by a small length of a conductor carrying a time varying current is
The left side of this equation is the electrical field of the electromagnetic wave radiated by a small length of conductor. The index reminds that the field is perpendicular to the line to the source. The reminds that this is the field observed seconds after the evaluation on the current derivative. The angle is the angle between the direction of the current and the direction to the point where the field is measured.
The electrical field and the radiated power are maximal in the plane perpendicular to the current element. They are zero in the direction of the current.
Only time-varying currents radiate electromagnetic power.
If the current is sinusoidal, it can be written in complex form, in the same way used for impedances. Only the real part is physically meaningful:
- is the amplitude of the current.
- is the angular frequency.
The (small) electric field of the electromagnetic wave radiated by an element of current is:
And for the time :
The electric field of the electromagnetic wave radiated by an antenna formed by wires is the sum of all the electric fields radiated by all the small elements of current. This addition is complicated by the fact that the direction and phase of each of the electric fields are, in general, different.
Although any circuit can radiate if driven with a signal of high enough frequency, most practical antennas are specially designed to radiate efficiently at a particular frequency. An example of an inefficient antenna is the simple Hertzian dipole antenna, which radiates over wide range of frequencies and is useful for its small size. A more efficient variation of this is the half-wave dipole, which radiates with high efficiency when the signal wavelength is twice the electrical length of the antenna.
One of the goals of antenna design is to minimize the reactance of the device so that it appears as a resistive load. An "antenna inherent reactance" includes not only the distributed reactance of the active antenna but also the natural reactance due to its location and surroundings (as for example, the capacity relation inherent in the position of the active antenna relative to ground). Reactance diverts energy into the reactive field, which causes unwanted currents that heat the antenna and associated wiring, thereby wasting energy without contributing to the radiated output. Reactance can be eliminated by operating the antenna at its resonant frequency, when its capacitive and inductive reactances are equal and opposite, resulting in a net zero reactive current. If this is not possible, compensating inductors or capacitors can instead be added to the antenna to cancel its reactance as far as the source is concerned.
Once the reactance has been eliminated, what remains is a pure resistance, which is the sum of two parts: the ohmic resistance of the conductors, and the radiation resistance. Power absorbed by the ohmic resistance becomes waste heat, and that absorbed by the radiation resistance becomes radiated electromagnetic energy. The greater the ratio of radiation resistance to ohmic resistance, the more efficient the antenna.
Effect of ground
At frequencies used in antennas, the ground behaves mainly as a dielectric. The conductivity of ground at these frequencies is negligible. When an electromagnetic wave arrives at the surface of an object, two waves are created: one enters the dielectric and the other is reflected. If the object is a conductor, the transmitted wave is negligible and the reflected wave has almost the same amplitude as the incident one. When the object is a dielectric, the fraction reflected depends (among others things) on the angle of incidence. When the angle of incidence is small (that is, the wave arrives almost perpendicularly) most of the energy traverses the surface and very little is reflected. When the angle of incidence is near 90° (grazing incidence) almost all the wave is reflected.
Most of the electromagnetic waves emitted by an antenna to the ground below the antenna at moderate (say < 60°) angles of incidence enter the earth and are absorbed (lost). But waves emitted to the ground at gracing angles, far from the antenna, are almost totally reflected. At grazing angles, the ground behaves as a mirror. Quality of reflection depends on the nature of the surface. When the irregularities of the surface are smaller than the wavelength reflection is good.
The wave reflected by earth can be considered as emitted by the image antenna.
This means that the receptor "sees" the real antenna and, under the ground, the image of the antenna reflected by the ground. If the ground has irregularities, the image will appear fuzzy.
If the receiver is placed at some height above the ground, waves reflected by ground will travel a little longer distance to arrive to the receiver than direct waves. The distance will be the same only if the receiver is close to ground.
In the drawing at right, we have drawn the angle far bigger than in reality. Distance between the antenna and its image is .
Situation is a bit more complex because the reflection of electromagnetic waves depends on the polarization of the incident wave. As the refractive index of the ground (average value ) is bigger than the refractive index of the air (), the direction of the component of the electric field parallel to the ground inverses at the reflection. This is equivalent to a phase shift of radians or 180°. The vertical component of the electric field reflects without changing direction. This sign inversion of the parallel component and the non-inversion of the perpendicular component would also happen if the ground were a good electrical conductor.
The vertical component of the current reflects without changing sign. The horizontal component reverses sign at reflection.
This means that a receiving antenna "sees" the image antenna with the current in the same direction if the antenna is vertical or with the current inverted if the antenna is horizontal.
For a vertical polarized emission antenna the far electric field of the electromagnetic wave produced by the direct ray plus the reflected ray is:
The sign inversion for the parallel field case just changes a cosine to a sinus:
In these two equations:
- is the electrical field radiated by the antenna if there were no ground.
- is the wave number.
- is the wave length.
- is the distance between antenna and its image (twice the height of the center of the antenna).
Radiation patterns of antennas and their images reflected by the ground. At left the polarization is vertical and there is always a maximum for . If the polarization is horizontal as at right, there is always a zero for .
For emitting and receiving antenna situated near the ground (in a building or a mast) far form each other, distances traveled by direct and reflected rays are nearly the same. There is no induced phase shift. If the emission is polarized vertically the two fields (direct and reflected) adds and there is maximum of received signal. Is the emission is polarized horizontally the two signals subtracts and the received signal is minimum. This is depicted in the image at right. In the case of vertical polarization, there is always a maximum at earth level (left pattern). For horizontal polarization, there is always a minimum at earth level. Note that in these drawings the ground is considered as a perfect mirror, even for low angles of incidence. In these drawings the distance between the antenna and its image is just a few wavelengths. For greater distances, the number of lobes increases.
Note that the situation is different – and more complex – if reflections in the ionosphere occur. This happens over very long distances (thousands of kilometers). There is not a direct ray but several reflected rays that add with different phase shifts.
This is the reason why almost all public address radio emissions have vertical polarization. As public uses to be near ground, horizontal polarized emissions would be poorly received. Observe household and automobile radio receivers. They all have vertical antennas or horizontal ferrite antennas for vertical polarized emissions. In cases where the receiving antenna must work in any position, as in mobile phones, the emitter and receivers in base stations use circular polarized electromagnetic waves.
Classical (analog) television emissions are an exception. They are almost always horizontally polarized, because the presence of buildings makes it unlikely that a good emitter antenna image will appear. However, these same buildings reflect the electromagnetic waves and can create ghost images. Using horizontal polarization, reflections are attenuated because of the low reflection of electromagnetic waves whose magnetic field is parallel to the dielectric surface near the Brewster's angle. Vertically polarized analog television has been used in some rural areas. In digital terrestrial television reflections are less annoying because of the type of modulation.
Mutual impedance and interaction between antennas
Current circulating in any antenna induces currents in all others. One can postulate a mutual impedance between two antennas that has the same significance as the in ordinary coupled inductors. The mutual impedance between two antennas is defined as:
where is the current flowing in antenna 1 and is the voltage that would have to be applied to antenna 2 – with antenna 1 removed – to produce the current in the antenna 2 that was produced by antenna 1.
From this definition, the currents and voltages applied in a set of coupled antennas is:
Mutual impedance between parallel dipoles not staggered. Curves Re and Im are the resistive and reactive parts of the impedance.
- is the voltage applied to the antenna
- is the impedance of antenna
- is the mutual impedance between antennas and
Note that, as is the case for mutual inductances,
If some of the elements are not fed (there is a short circuit instead a feeder cable), as is the case in television antennas (Yagi-Uda antennas), the corresponding are zero. Those elements are - unfairly - called parasitic elements.
In some geometrical settings, the mutual impedance between antennas can be zero. This is the case for crossed dipoles used in circular polarization antennas.
- Category:Radio frequency antenna types
- Category:Radio frequency propagation
- List of antenna terms
- Satellite television
- Amateur radio
- RF connector
- Antenna Measurements
- Cellular repeater
External articles and further reading
- General references and footnotes
- ^ In the context of 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 John D. Kraus of the Ohio State University. Besides the title, Dr. Kraus noted this in a footnote on the first page of his book. Insects may have "antennae" but not in technical contexts.
- ^ "Salvan: Cradle of Wireless, How Marconi Conducted Early Wireless Experiments in the Swiss Alps", Fred Gardiol & Yves Fournier, Microwave Journal, February 2006, pp. 124-136.
- "Practical antennas" references
- How to Become An Antenna Guru by Dan Warren
- Why an Antenna Radiates at ARRL
- Why Antennas Radiate, Stuart G. Downs, WY6EE (PDF)
- Understanding electromagnetic fields and antenna radiation takes (almost) no math, Ron Schmitt, EDN Magazine, March 2 2000 (PDF)
- General websites
- "Antenna". Hamradio, Hamradio.co.in. (ed. Antenna for Ham / Amateur Radio)
- "Ham radio guide : Antennas". The DXZone.com, 2006. (ed. Amateur radio antenna plans and documents)
- "Ham Radio Antennas" NØHR.com, 2006.(ed. Ham radio antenna sites sorted by band, design, and homebrew vs. commercial antenna products.)
- Ian Poole (editor), "Antenna topics". Adrio Communications Ltd. (ed. Information regarding antennas)
- SWDXER ¨The SWDXER¨ - with general SWL information and radio antenna tips.
- Theory and simulations
- Sophocles J. Orfanidis, "Electromagnetic Waves and Antennas", Rutgers University (20 PDF Chaps. Basic theory, definitions and reference)
- Hans Lohninger, "Learning by Simulations: Physics: Coupled Radiators". vias.org, 2005. (ed. Interactive simulation of two coupled antennas)
- Justin Smith "Aerials". A.T.V (Aerials and Television), 2006. (ed. Article on the (basic) theory and use of TV aerials)
- Antennas Research Group, "Virtual (Reality) Antennas". Democritus University of Thrace, 2005.
- "Support > Knowledgebase > RF Basics > Antennas / Cables > dBi vs. dBd detail". MaxStream, Inc., 2005. (ed. How to measure antenna gain)
- Patents and USPTO
- CLASS 343, Communication: Radio Wave Antenna
- Effect of ground references
- Electronic Radio and Engineering. F.R. Terman. MacGraw-Hill
- Lectures on physics. Feynman, Leighton and Sands. Addison-Wesley
- Classical Electricity and Magnetism. W. Panofsky and M. Phillips. Addison-Wesley
Categories: Radio frequency antennas | Amateur radio | Radio electronics