Glossary of commonly used RF terminology
A
- Acceptance Pattern
- Of an antenna, for a given plane, a distribution plot of the off-axis power relative to the on-axis power as a function of angle or position. Note: The acceptance pattern is the equivalent of a horizontal or vertical antenna pattern. Of an optical…
- Access Point
- A device that transports data between a wireless network and a wired network (infrastructure).
- Adaptive (Smart) Antenna
- An antenna system having circuit elements associated with its radiating elements such that one or more of the antenna properties are controlled by the received signal.
- Antenna
- An electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter applies an oscillating radio frequency electric current to…
- Antenna Directivity
- The directivity of a wireless antenna is given by the ratio of the maximum radiation intensity (power per unit solid angle) to the average radiation intensity (averaged over a sphere). The directivity of any source, other than isotropic, is always…
- Antenna Efficiency
- The total antenna efficiency accounts for the following losses: (1) reflection because of mismatch between the feeding transmission line and the antenna and (2) antenna conductor and dielectric losses.
- Antenna Gain
- The maximum gain of a wireless antenna is simply defined as the product of the directivity by efficiency. If the efficiency is not 100 percent, the antenna gain is less than the directivity. When the reference is a lossless isotropic antenna, the…
- Antenna Polarization
- In a specified direction from a wireless antenna and at a point in its far field, is the polarization of the (locally) plane wave which is used to represent the radiated wave at that point. At any point in the far-field of an antenna the radiated…
- Aperiodic Antenna
- Antenna designed to have constant impedance over a wide range of frequencies because of the suppression of reflections within the antenna system. Includes terminated wave and rhombic antennas.
- Aperture (Antenna)
- A measure of how effective an antenna is at receiving the power of radiowaves. The aperture is defined as the area, oriented perpendicular to the direction of an incoming radio wave, which would intercept the same amount of power from that wave as…
- Aperture Illumination
- The ratio of the directivity of the AUT compared to the directivity of a uniformly illuminated ideal antenna of the same aperture size.
- Aperture-to-medium Coupling Loss
- The difference between the theoretical gain of a very large antenna, such as the antennas in beyond-the-horizon microwave links, and the gain that can be realized in practice.
- Attenuation
- The loss in power of electromagnetic signals between transmission and reception points.
- Azimuth
- Horizontal direction expressed as the angular distance between the direction of a fixed point (as the observer´s heading) and the direction of the object.
B
- Bandwidth
- A range of consecutive frequencies comprised of a band (i.e. the US cellular bandwidth is 72 MHz wide between the frequencies of 824 MHz - 890 MHz) over which an antenna shall perform without the need of any adjustment.
- Beam Antenna
- An antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources. <img…
- Beam Diameter
- See also: Beamwidth
- Beam Divergence
- An angular measure of the increase in beam diameter or radius with distance from the optical aperture or antenna aperture from which the electromagnetic beam emerges. The term is relevant only in the "far field", away from any focus of the beam.
- Beam Steering
- Changing the direction of the main lobe of a radiation pattern.
- Beamwidth
- In an antenna pattern, the beamwidth is the size of the angle between the half-power (-3 dB) points of the main lobe, when referenced to the peak effective radiated power of the main lobe.
- Biconical Antenna
- A broad-bandwidth antenna made of two roughly conical conductive objects, nearly touching at their points. Biconical antennas are broadband dipole antennas, typically exhibiting a bandwidth of 3 octaves or more.
- Billboard Antenna
- An aerial half a wavelength long antenna consisting of two rods connected to a transmission line at the center.
- Boresight
- The axis of maximum gain (maximum radiated power) of a directional antenna.
C
- Cable Loss
- A numeric value describing the amount of signal loss from one point on a length of cable to another. This is measured in decibels (dB).
- Cassegrain Antenna
- A parabolic antenna in which the feed radiator is mounted at or behind the surface of the concave main parabolic reflector dish and is aimed at a smaller convex secondary reflector suspended in front of the primary reflector. The beam of radio waves…
- Co-Polarization
- That polarization which the antenna is intended to radiate.
- Coaxial Cable
- A type of cable which contains two conductors, one inside and the other outside around it, separated by an insulating layer. They share the same axis and are concentric. Coaxial cable "co-ax" is commonly used in cable-TV and Ham radio…
- Coaxial Dipole Antenna
- An antenna comprised of a extension to the inner conductor of a coaxial line and a radiating sleeve which in effect is formed by folding back the outer conductor of the coaxial line.
- Collinear Antenna Array
- An array of dipole antennas mounted in such a manner that the corresponding elements of each antenna are parallel and collinear, that is they are located along a common line or axis. A collinear array is usually mounted vertically, in order to…
- Collinear Array Antenna
- A linear array of radiating elements, usually dipoles, with their axes lying in a straight line. Collinear arrays are usually found in omnidirectional antennas.
- Corner Reflector
- A retroreflector consisting of three mutually perpendicular, intersecting flat surfaces, which reflects waves back directly towards the source, but shifted (translated). The three intersecting surfaces often have square shapes. Radar corner…
- Counterpoise
- A type of electrical ground that is not connected to earth. It is used in radio antenna systems when a normal earth ground cannot be used because of high soil resistance. It consists of a network of wires or cables (or a metal screen) running…
- CPE Antenna
- Customer premises antenna, usually a small directional antenna which points to an access point.
- Cross-Polarization
- In a specified plane containing the reference polarization ellipse, the polarization orthogonal to a specified reference polarization. The reference polarization is usually the co-polarization.
D
- dBi
- The dB power relative to an isotropic source.
- dBm
- A measure of power based upon the decibel scale, but referenced to the milliWatt: i.e. 1 dBm = .001 Watt. dBm is often used to describe absolute power level where the point of reference is 1 milliWatt. In high power applications the dBW is often…
- dBW
- The ratio of the power to 1 Watt expressed in decibels. dc ground An antenna which is a dead short to a DC current, and has a shunt-fed design. To RF it is not seen as a short.
- Decibels (dB)
- dBd Quantification of the gain for an antenna in comparison with the gain of a dipole.
- Departure Angle
- Angle at which the radiated beam leaves the antenna.
- Despun Antenna
- Satellite-based directional antenna pointed continuously at earth by electrically or mechanically despinning the antenna at the same rate that the satellite is spinning for stabilization.
- Diplex Operation
- Simultaneous transmission or reception of two signals using a specified common element, such as a single antenna or a single carrier.
- Dipole Antenna
- A radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other (in line with each other), with a small space between them. The…
- Direct Ray
- A ray that does not reflect off of anything nor is diffracted on its way from the source to the receptor.
- Directional Antenna
- An antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources.
- Driven Element
- A radiator element of an antenna system to which the transmission line is connected.
- Driven Element
- The element in the antenna (typically a metal rod) which is electrically connected to the receiver or transmitter.
E
- E-Plane
- For a linearly polarized antenna, the plane containing the electric field vector and the direction of maximum radiation. For a vertically-polarized WLAN antenna, the E-plane usually coincides with the vertical/elevation plane
- Effective Antenna Gain Contour (Of A Steerable Satellite Beam)
- An envelope of antenna gain contours resulting from moving the boresight of a steerable satellite beam along the limits of the effective boresight area.
- Effective Boresight Area (Of A Steerable Satellite Beam)
- An area on the surface of the Earth within which the boresight of a steerable satellite beam is pointed. There also may be more than one unconnected effective boresight area to which a single steerable satellite beam can be pointed.
- Effective Height
- The physical height of an antenna.
- Effective Isotropically Radiated Power (E.I.R.P.)
- The amount of power that a theoretical isotropic antenna (which evenly distributes power in all directions) would emit to produce the peak power density observed in the direction of maximum antenna gain. EIRP can take into account the losses in…
- Effective Monopole Radiated Power (E.M.R.P.)
- Used in Europe, especially in relation to mediumwave broadcasting antennas. This is the same as Effective Radiated Power (E.R.P.), except that a short vertical antenna (i.e. a short monopole) is used as the reference antenna instead of a half-wave…
- Effective Radiated Power (E.R.P.)
- A standardized theoretical measurement of radio frequency energy and is determined by subtracting system losses and adding system gains. ERP takes into consideration transmitter power output (TPO), transmission line attenuation (electrical…
- Efficiency
- The ratio of useful output to input power, determined in antenna systems by losses in the system including losses in nearby objects.
F
- Fan-beam Antenna
- A directional antenna which produces a main beam having a narrow beamwidth in one dimension and a wider beamwidth in the other dimension. This pattern will be achieved by a truncated paraboloid reflector or a circular paraboloid reflector. Since the…
- Far-field Radiation Pattern
- A radiation pattern measured at the far field of an antenna or other emitter.
- Far-Field Region
- Generally refers to the distance an antenna is being measured from. These areas are generally determined by the size of the wave. The distance of one wavelength is generally referred to as “near-field” while two wavelengths is generally referred…
- Feed
- Refers to the components of an antenna which feed the radio waves to the rest of the antenna structure, or in receiving antennas collect the incoming radio waves, convert them to electric currents and transmit them to the receiver.
- Fractal Antenna
- An antenna that uses a fractal, self-similar design to maximize the length, or increase the perimeter (on inside sections or the outer structure), of material that can receive or transmit electromagnetic radiation within a given total surface area…
- Frequency
- The number of cycles per second of a sound wave.
- Frequency Bandwidth
- The range of frequencies within which the performance of the antenna, with respect to some characteristics, conforms to a specified standard. Voltage Standing Wave Ratio (VSWR) of a wireless antenna is the main bandwidth limiting factor. See also:…
- Fresnel Zone
- The area around the visual line-of-sight that radio waves spread out into after they leave the antenna. This area must be clear or else signal strength will weaken. (Pronounced "Fre-nel" with a silent "s".)
- Front-to-back Ratio
- Describes the ratio of power gain between the front and rear of a directional antenna. In other words, the ratio of received-signal strength when the antenna is rotated 180º backwards.
G
- Gain
- The maximum gain of a wireless antenna is simply defined as the product of the directivity by efficiency. If the efficiency is not 100 percent, the antenna gain is less than the directivity. When the reference is a lossless isotropic antenna, the…
- Gain Pattern
- Normalizing the power/field to that of a reference antenna yields a gain pattern. When the reference is an isotropic antenna, the gain is expressed in dBi. When the reference is a half-wave dipole in free space, the gain is expressed in dBd.
- Ground Plane
- There are a variety of ground planes, including drooping ground planes, and flat circular ground plane antennas. A ground plane may consist of a natural surface, such as the Earth (or ocean) (or salt marsh) or an artificial surface of opportunity…
H
- H-Plane
- For a linearly polarized antenna, the plane containing the magnetic field vector and the direction of maximum radiation. For a vertically-polarized WLAN antenna, the H-plane usually coincides with the horizontal/azimuth plane.
- Half-Power Beamwidth (HPBW)
- In a radiation pattern cut containing the direction of the maximum of a lobe, the angle between the two directions in which the radiation intensity is one-half the maximum value. The Half-power beamwidth is also commonly referred to as the 3-dB…
- Half-Wave Dipole
- A wire antenna consisting of two straight collinear conductors of equal length, separated by a small feeding gap, with each conductor approximately a quarter-wave length long. See also: Dipole Antenna
- Helical Antenna
- An antenna consisting of a conducting wire wound in the form of a helix.
- Heterodyne Repeater
- A radio repeater in which the received radio signals are converted to an intermediate frequency, amplified, and reconverted to a new frequency band for transmission over the next repeater section.
- Horn Antenna
- An antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz.
- Hybrid Coupler
- A type of directional coupler where the input power is equally divided between two output ports.
I
- Image Antenna
- An electrical mirror-image of an antenna element formed by the radio waves reflecting from a conductive surface called a ground plane, such as the surface of the earth. It is used as a geometrical technique in calculating the radiation pattern of…
- Impedance
- The Ohmic value of an antenna feed point, matching section or transmission line at a radio frequency. An impedance may contain a reactance as well as a resistance component.
- Input Impedance
- The impedance presented by an antenna at its terminals. The input impedance is a complex function of frequency with real and imaginary parts. The input impedance is graphically displayed using a Smith chart.
- Intermediate-field Region
- Also referred to as the Transition Zone or Near-far Field. This is the area between near and far field. However, the near-field does not suddenly end where the far-field begins. Rather, there is a transition zone between these types where both…
- Isolation
- A measure of power transfer from one antenna to another. This is also the ratio of the power input to one antenna to the power received by the other antenna, expressed in decibels (dB). The same definition is applicable to two-port antennas such as…
- Isotropic Antenna
- A theoretical source which radiates the same intensity of radiation in all directions. It has no preferred direction of radiation and radiates uniformly in all directions over a sphere centred on the source. Isotropic radiators are used as reference…
L
- Load
- The electrical entity to which power is delivered. The antenna system is a load for a transmitter.
- Lobe
- The radiation pattern of most antennas shows a pattern of "lobes" at various angles/directions where the radiated signal strength reaches a maximum, separated by "nulls", angles at which the radiation falls to zero. In a directional antenna the…
- Log-periodic Antenna (Lp)
- A broadband, multi-element, directional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency. The individual components are often dipoles, as in a…
- Loop
- A radio antenna consisting of a loop (or loops) of wire, tubing, or other electrical conductor with its ends connected to a balanced transmission line. Within this physical description there are two very distinct antenna designs: the small loop (or…
M
- Microstrip Antenna
- A wireless antenna which consists of a thin metallic conductor bonded to a thin grounded dielectric substrate. An example of such antenna is the microstrip patch.
- Monopole
- Literally, one pole, such as a vertical radiator operated against the earth or a ground plane. A handheld rubber duck type of antenna will most likely be a monopole.
- Multi-element Dipole Antenna
- An antenna consisting of an arrangement of multiple dipole antennas. Note: Various directivity patterns may be obtained by varying the arrangement of the dipoles and the way they are driven.
- Multi-Path Propagation
- The result of interference from reflections off surfaces surrounding the antenna. This interference changes the target´s return signal strength. Sometimes it is stronger and sometimes weaker than expected. The degree of multi-path propagation…
- Multicoupler
- A device which splits the source signal into many separate receiver connections.
N
- Near-field Region
- Generally refers to the distance an antenna is being measured from. These areas are generally determined by the size of the wave. The distance of one wavelength is generally referred to as “near-field” while two wavelengths is generally referred…
- Noise
- Any unwanted and unmodulated energy that is always present to some extent within any signal.
- Normalized Pattern
- Normalizing the power / field with respect to its maximum value yields a normalized power / field pattern with a maximum value of unity (or 0 dB).
- Null
- Any area of the antenna which does not emit signal is considered a null or blind area.
- Null Filling
- The process to fill the nulls in the antenna radiation pattern to avoid blind spots in a coverage area.
O
- Omnidirectional Antenna
- An antenna which radiates radio wave power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis. This radiation pattern is often described…
- Orthomode Transducer
- A device that either combines or separates two microwave signal paths.
P
- Parabolic Antenna
- An antenna that uses a parabolic reflector (a curved surface with the cross-sectional shape of a parabola) to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish. These…
- Parasitic Element
- A conductive element, typically a metal rod, which is not electrically connected to anything else. The purpose of the parasitic elements is to modify the radiation pattern of the radio waves emitted by the driven element, directing them in a beam…
- Pentaband Antenna
- An antenna that combines 4-band GSM and W-CDMA 2100 to receive and transmit signals in all cellular bands. These antennas can be used in mobile, machine-to-machine, laptop, automotive, and all portable device applications for devices operating on…
- Periscope Antenna
- An antenna configuration in which the transmitting antenna is oriented to produce a vertical radiation pattern. A flat or off-axis parabolic reflector, mounted above the transmitting antenna, is used to direct the beam in a horizontal path toward…
- Phased Array
- An antenna array is a group of multiple active antennas coupled to a common source or load to produce a directive radiation pattern. Usually, the spatial relationship of the individual antennas also contributes to the directivity of the antenna…
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