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 fiber or fiber bundle, a curve of total transmitted power plotted against the launch angle.
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 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 greater than unity.
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 gain is expressed in dBi. When the reference is a half wave dipole antenna, the antenna gain is expressed in dBd (0 dBd = 2.15 dBi).
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 is produced by the antenna receiving it.
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.
Beam Diameter
See 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 from the feed illuminates the secondary reflector, which reflects it back to the main reflector dish, which reflects it forward again to form the desired beam.
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 applications.
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 increase overall gain and directivity in the horizontal direction.
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 reflectors made of metal are used to reflect radio waves from radar sets.
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 parallel to the ground, suspended from a few centimetres to several metres above the ground (or lying on the surface). The counterpoise functions as one plate of a large capacitor, with the conductive layers of the earth acting as the other.
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 used with a reference of 1 Watt.
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.

D

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 radio frequency voltage is applied to the antenna at the center, between the two conductors. These antennas are the simplest practical antennas from a theoretical point of view. They are used alone as antennas, notably in traditional "rabbit ears" television antennas
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
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 transmission line and connectors and includes the gain of the antenna. The EIRP is often stated in terms of decibels over a reference power emitted by an isotropic radiator with an equivalent signal strength.
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 dipole.
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 resistance and RF radiation), RF connector insertion losses, and antenna directivity, but not height above average terrain (HAAT).
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 reflector is narrow in the vertical plane and wide in the horizontal, it produces a beam that is wide in the vertical plane and narrow in the horizontal. (The larger the antenna dimension, the narrower the beam.)
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 to as the transition zone. Anything beyond (into infinity) is referred to as the far-field.
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 or volume.
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.
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 is expressed in dBi. When the reference is a half wave dipole antenna, the antenna gain is expressed in dBd (0 dBd = 2.15 dBi).
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 (such as the roof of a motor vehicle). A ground plane can also be a specially designed artificial surface (such as the radial elements of a quarter-wave ground plane antenna). Artificial (or substitute) grounds (e.g., ground planes) concerns the grounding structure for the antenna and includes the conductive structure used in place of the earth and which grounding structure is distinct from the earth.

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 beamwidth. Beamwidth typically decreases as antenna gain increases.
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.
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 the antenna.
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 types of EM field-effects may be significant.
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 dual-polarization or dual-band antennas.
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 radiators with which other sources are compared.

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 objective is to emit the radio waves in one direction, so the lobe in that direction is designed to be bigger than the others. This is referred to as the main lobe. The other lobes are called "sidelobes", and usually represent unwanted radiation in undesired directions. The sidelobe in the opposite direction from the main lobe is called the "backlobe".
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 log-periodic dipole array (LPDA). Log-periodic antennas are designed to be self-similar and are thus also fractal antenna arrays.
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 magnetic loop) with a size much smaller than a wavelength, and the resonant loop antenna with a circumference approximately equal to the wavelength.

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.
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 to as the transition zone. Anything beyond (into infinity) is referred to as the far-field.
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

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 antennas have some of the highest gains, that is they can produce the narrowest beam width angles, of any antenna type.
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 GSM bands (GSM850, EGSM900, PCN1800, PCS1900) and W-CDMA 2100. They meet the need for small, high-efficiency, all cellular band antennas.
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 the receiving antenna. A periscope antenna facilitates increased terrain clearance without long transmission lines, while permitting the active equipment to be located at or near ground level for ease of maintenance.
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 array.
Planar Array
An antenna in which all of the elements, both active and parasitic, are in one plane. A planar array provides a large aperture and may be used for directional beam control by varying the relative phase of each element. A planar array may be used with a reflecting screen behind the active plane.
Point-to-Multipoint
A communications channel running from one point to several other points.
Point-to-Point
A long-range wireless network between two points. Point-to-point wireless networks use directional antennas.
Power Handling
Is the ability of a Wireless LAN antenna to handle high power without failure. High power in antenna can cause voltage breakdown and excessive heat (due to conductor and dielectric antenna losses) which would result in an antenna failure.
Printed Antenna
All antennas made by means of a printed circuit process.
Propagation Mode
The manner in which radio signals travel from a transmitting antenna to a receiving antenna (such as ground wave, sky wave, direct wave, ground reflection, or scatter).

R

Radiation Efficiency
The ratio of the total power radiated by a Wireless LAN antenna to the net power accepted by the antenna from the connected transmitter.
Radiation Pattern
The variation of the field intensity of an antenna as an angular function with respect to the axis. A radiation pattern is usually represented graphically for the far-field conditions in either horizontal or vertical plane.
Radiation Resistance
The resistance that, if inserted in place of an antenna, would consume the same amount of power that is radiated by the antenna.
Radio Beam
A radiation pattern from a directional antenna, such that the energy of the transmitted electromagnetic wave is confined to a small angle in at least one dimension.
Radio Horizon
The locus of points at which direct rays from an antenna are tangential to the surface of the Earth. (188) Note: If the Earth were a perfect sphere and there were no atmospheric anomalies, the radio horizon would be a circle. In practice, the distance to the radio horizon is affected by the height of the transmitting antenna, the height of the receiving antenna, atmospheric conditions, and the presence of obstructions, e.g., mountains.
Radio Horizon Range (Rhr)
The distance at which a direct radio wave can reach a receiving antenna of given height from a transmitting antenna of given height.
Radome
A typically rigid dielectric cover over the radiating portion of an antenna, and nearly always separated from the radiator by an air gap. A radome (the merger of radar and dome) has the purpose of protecting the radiator from natural weather phenomena and contamination by dirt. It usually includes aerodynamic shaping to minimize wind loading.
Receiver (Rx)
An electronic device which enables a particular signal to be separated from all and converts the signal format into a format for video, voice or data.
Reference Antenna
An antenna with known performance normally used to calibrate other systems.
Reflective Array Antenna
An antenna in which multiple driven elements are mounted in front of a surface designed to reflect the radio waves in a desired direction. Reflective array antennas usually have many driven elements working in conjunction with a flat, electrically large reflecting surface to produce a unidirectional beam, increasing antenna gain and reducing radiation in unwanted directions. These are also called "billboard antennas".
Relative Antenna Power Gain
The ratio of the average radiation intensity of the test antenna to the average radiation of a reference antenna with all other conditions remaining equal.
Rhombic Antenna
A broadband directional antenna most commonly used in HF (high frequency or shortwave) ranges. It is named after its "rhombic" diamond shape, with each side typically at least one wavelength (λ) or longer in length. Each vertex is supported by a pole, typically at least one wavelength high. A horizontal rhombic antenna (picture below) radiates horizontally polarised waves. Its principal advantages over other choices of antenna are its simplicity, high forward gain and the ability to operate over a wide range of frequencies.

S

Sectorial Antenna
A directive antenna with a radiation pattern aperture (3 dB beamwidth) larger than 45°. Sectorial antennas are generally used for point-to-multipoint systems or combined with several antennas to create a base station.
Shadow Loss
1. The attenuation caused to a radio signal by obstructions in the propagation path. 2. In a reflector antenna, the relative reduction in the effective aperture of the antenna caused by the masking effect of other antenna parts, such as a feed horn or a secondary reflector, which parts obstruct the radiation path.
Shield Effectiveness
A measurement of how well the shielding material (braid, solid tape, etc.) protects the external environment from radiation produced by the center conductor.
Side 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 objective is to emit the radio waves in one direction, so the lobe in that direction is designed to be bigger than the others. This is referred to as the main lobe. The other lobes are called "sidelobes", and usually represent unwanted radiation in undesired directions. The sidelobe in the opposite direction from the main lobe is called the "backlobe".
Side Lobe Level (SLL)
The ratio, in decibels (dB), of the amplitude at the peak of the main lobe to the amplitude at the peak of a side lobe.
Side Lobe Suppression
Any process, action or adjustment to reduce the level of the side lobes or to reduce the degradation of the intended antenna system performance resulting from the presence of side lobes. For WLAN antennas, the first side lobe above the horizon is preferred to be low in order to reduce interference to adjacent sites. At the other hand, the side lobes below the horizon are preferred to be high for better coverage.
Single-polarized Antenna
An antenna that radiates or receives radio waves with a specific polarization. Note: For a singly polarized antenna, the desired sense of polarization is usually maintained only for certain directions or within the major portion of the radiation pattern.
Skip Zone
An annular region within the transmission range of an antenna, within which signals from the transmitter are not received. Note: The skip zone is bounded by the locus of the farthest points at which the ground wave can be received and the nearest points at which reflected sky waves can be received.
Sky Wave
A radio wave that travels upward from the antenna and may be reflected to Earth by the ionosphere.
Slewing
1. Rotating a directional antenna or transducer rapidly about one or more axes. 2. Changing the frequency or pulse repetition rate of a signal source. 3. Changing the tuning of a receiver, usually by sweeping through many or all frequencies. 4. Redirecting the beam of a fixed antenna array by changing the relative phases of the signals feeding the antenna elements.
Slot Antenna
A radiating element formed by a slot in a conducting surface or in the wall of a waveguide.
Slotted Waveguide
A slotted waveguide has no reflector but emits directly through the slots. The spacing of the slots is critical and is a multiple of the wavelength used for transmission and reception.
Space Diversity
Also known as antenna diversity, is any one of several wireless diversity schemes that uses two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and indoor environments, there is no clear line-of-sight (LOS) between transmitter and receiver. Instead the signal is reflected along multiple paths before finally being received. Each of these bounces can introduce phase shifts, time delays, attenuations, and distortions that can destructively interfere with one another at the aperture of the receiving antenna. Antenna diversity is especially effective at mitigating these multipath situations.
Spillover
In an antenna, the part of the radiated energy from the feed that does not impinge on the reflectors.
Spot Beam
In satellite communications systems, a narrow beam from a satellite station antenna that illuminates, with high irradiance, a limited area of the Earth by using beam (directive) antennas rather than Earth-coverage antennas.
Standing Wave Ratio (SWR)
Voltage Standing Wave Ratio (VSWR)

T

Test Antenna
An antenna of known performance characteristics used in determining transmission characteristics of equipment and associated propagation paths.
Transmission Line
The connecting link allowing the radio frequency energy generated by the radio to be delivered to the antenna. (Coaxial cable, microstrip or coplanar lines in our industry.)
Transmitter
An electronic device consisting of oscillator, modulator and other circuits which produce a radio electromagnetic wave signal for radiation into the atmosphere by an antenna.

U

Uniform Linear Array
An antenna composed of a relatively large number of usually identical elements arranged in a single line or in a plane with uniform spacing and usually with a uniform feed system.

V

Voltage Standing Wave Ratio (VSWR)
The ratio of the maximum/minimum values of standing wave pattern along a transmission line to which a load is connected. VSWR value ranges from 1 (matched load) to infinity for a short or an open load. For most Wireless LAN antennas the maximum acceptable value of VSWR is 2.0. VSWR of 1.5 or less is excellent. This is approximately the same as a Return Loss of 14.5 dB. What this means is that most of the signal from the transmitter to the antenna is being radiated. (96% radiated and 4% reflected) A VSWR of 2.0 (return loss of 9.5 dB) means that 90% is radiated and 10% reflected.

W

Waveguide
A material medium that confines and guides a propagating electromagnetic wave. In the microwave regime, a waveguide normally consists of a hollow metallic conductor, usually rectangular, elliptical, or circular in cross section. This type of waveguide may, under certain conditions, contain a solid or gaseous dielectric material.
Waveguide Antenna
Also known as a "cantenna", it is a directional waveguide antenna for long-range Wi-Fi used to increase the range of (or to discover) wireless networks.
Whip
The vertical portion of the antenna assembly acting as the radiator of the radio frequency energy.
Whip Antenna
A whip antenna is the most common example of a monopole antenna, an antenna with a single driven element and a ground plane (usually a flexible rod).

Y

Yagi Antenna
A highly directional radio antenna made of several short rods mounted across an insulating support and transmitting or receiving a narrow band of frequencies.