Glossary - antenna

Adaptive Multiple Input Multiple Output (A-MIMO or Adaptive MIMO) is a scheme to enhance the MIMO technology by employing adaptive coding and modulation techniques for the purpose of improving channel capacity, diversity, and robustness of wireless communications. In an adaptive MIMO system, the system parameters are jointly optimised to adapt to the changing channel conditions through link adaptation techniques that can track the time-varying characteristics of the wireless channel. The goal is to maximise the resources available in multiple antenna channels by using optimal schemes at all times.

Adaptive Antenna System (AAS), also called Advanced Antenna System, is a technology that enables network operators to increase the wireless network capacity. In addition, Adaptive Antenna Systems offer the potential of increased spectrum efficiency, extended range of coverage and higher rate of frequency reuse. Adaptive Antenna Systems consist of multiple antenna elements at the transmitting and/or receiving side of the communication link, whose signals are processed adaptively in order to exploit the spatial dimension of the mobile radio channel. Depending on whether the processing is performed at the transmitter, receiver, or both ends of the communication link, the adaptive antenna technique is defined as Multiple-Input Single-Output (MISO), Single-Input Multiple-Output (SIMO), or Multiple-Input Multiple-Output (MIMO).

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.

Adaptive array antenna is a type of advanced smart antenna technology that continually monitors a received signal and dynamically adapts signal patterns to optimise wireless system performance. The arrays use signal processing algorithms to adapt to user movement, changes in the radio-frequency environment and multi-path and co-channel interference.

Adaptive MIMO Switching (AMS) is used to switch between multiple MIMO modes to maximise spectral efficiency without reducing the area of coverage.. In an adaptive MIMO switching system, the system parameters are jointly optimised to adapt to the changing channel conditions through link adaptation techniques that can track the time-varying characteristics of the wireless channel. The goal is to maximise the resources available in multiple antenna channels by using optimal schemes at all times.

Angle diversity is a technique using multiple antenna beams to receive multipath signals arriving at different angles.

A metallic device used in the transmission and reception of electromagnetic waves. An antenna is a passive or an active device which permits transmission.

Antenna beamwidth, also known as the half-power beamwidth, is the angle of an antenna pattern or beam over which the relative power is at or above 50% of the peak power.

Antenna directivity, also known as antenna gain, is the relative gain of the main beam of an antenna pattern to a reference antenna, usually an isotropic or standard dipole.

The use of two or more antennas to improve signal quality.

The ratio of the antenna’s maximum radiation intensity in a stated direction to the maximum radiation intensity of a reference antenna (dipole, isotropic antenna) with identical power applied to both.

Access points act as a central transmitter and receiver of WLAN radio signals. Access points used in home or small business networks are generally small, dedicated hardware devices featuring a built-in network adapter, antenna and radio transmitter. Access points support Wi-Fi wireless communication standards.

The loss in power of electromagnetic signals between transmission and reception points.

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.

Bandwidth is the portion of the frequency spectrum required to transmit desired information. Each radio channel has a centre frequency and additional frequencies above and below this carrier frequency which is used to carry the transmitted information. The range of frequencies from the lowest to the highest used is called the bandwidth.

In a cellular communication system, a base station could be considered a central mode of transmission and reception for the network. This station includes an omni-directional antenna or several sectorial antennas.

The angle of signal coverage provided by an antenna. Beamwidth usually decreases as antenna gain increases.

Base station (BS), also called cell site, is the local cellular tower and radio antenna (including radios, controllers, switch interconnects, etc.) that handles communication with mobile users in a particular area or cell. A cellular network is made up of many cell sites or base stations, all connected back to the switch via landline or microwave.

A cable that is ready for installation in specific applications and usually terminated with connectors.

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).

A transmission line connection at the electrical centre of an antenna radiator.

A solid or stranded electrical conductor generally composed of copper and located at the centre of the coaxial cable.

A system of two or more antenna radiators arranged in a line and connected end-to-end to generate a directed field pattern (serial linear topology).

A metal body such as tubing, rod or wire which permits current to travel continuously along its length.

With reference to on-glass antennas, a coupler is the two-piece interface between the coaxial cable on the inside of the glass and the radiator on the outside of theglass. It is designed to efficiently couple RF energy through the glass. The formulation of the glass and glass thickness normally have a substantial effect on coupler performance.

A point of current maxima (antinode) on an antenna.

A point of current minima on an antenna.

Quantification of the gain for an antenna in comparison with the gain of a dipole.

The dB power relative to an isotropic source.

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.

The ratio of the power to 1 Watt expressed in decibels.

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.

The standard unit used to measure the intensity of a sound or the power level of an electrical signal by comparing it with a given level on a logarithmic scale.

An antenna - usually a half wavelength long - split at the exact centre for connection to a feed line. Also called a “doublet”.

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.

The theoretical characteristic of an antenna to concentrate power in only one direction, whether transmitting or receiving.

A radiator element of an antenna system to which the transmission line is connected.

In general Antenna measurements and radiation patterns in particular must be performed with polarisation in mind. Since polarisation is defined as having the same orientation as an antenna’s electric field vector, it is common practice to refer to measurements aligned with either the electric vector ( E-plane) or magnetic vector (H-plane).

The ratio of useful output to input power, determined in antenna systems by losses in the system, including losses in nearby objects.

Effective Isotropic Radiated Power (EIRP), also known as Equivalent Isotropically Radiated Power, is the amount of power that would have to be emitted by an isotropic antenna (that evenly distributes power in all directions and is a theoretical construct) 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 level, that would be the power emitted by an isotropic radiator with an equivalent signal strength. The EIRP allows comparisons between different emitters regardless of type, size or form. From the EIRP, and with knowledge of a real antenna's gain, it is possible to calculate real power and field strength values.

Some antennas (such as various low profile antennas, some base loaded whips and often rubber duckie portable antennas) are considerably smaller than either a 1/2 or 1/4 wavelength antenna. The challenge with electrically small antennas is to maintain radiating efficiency. A greater challenge is to design an antenna with adequate bandwidth. Careful design using high quality materials often overcome these obstacles.

Typically a subset or a more elementary part of a larger antenna system. For example, an element of a Yagi-Uda array is normally a dipole antenna that, together with other dipoles, forms the array. An 8-element Yagi antenna would then ordinarily have 8 dipoles.

Raises the radiating element above the vehicle roof level thereby reducing obstruction.

Antennas directly integrated into a system such as an access point, a terminal or a handset. In most cases, this antenna is matched to the system and cannot be used in other applications without modification.

An absolute measure in one direction of the electromagnetic wave field generated by an antenna at some distance away from the antenna.

Antennas identified as Field Tunable are shipped with a cutting chart which the installer uses to select a desired operating frequency by tuning the antenna to resonate. Cutting charts should be used as guidelines and are adequately accurate for many applications. However, Larsen recommends using appropriate RF measurement devices whenever possible for more accurate tuning.

Reductions in signal strength or quality is due to signal absorption by trees or foliage obstructions in the signal's line-of-sight path. For example, 800 MHz systems are seldom deployed in forested areas. Pine needles, nearly the same length as 800 MHz antenna,s can negatively affect signal reception in that band.

Frequency is the measurement of the number of times that a repeated event occurs per unit time. To calculate the frequency of an event, the number of occurrences of the event within a fixed time interval are counted, and then divided by the length of the time interval.

The gain of an antenna, in a specified direction.

The increase in signal strength that is produced by an amplifier. The ratio between the amount of energy propagated from an antenna that is directional compared to the energy from the same antenna that would be propagated if the antenna were not directional. The gain of an antenna is the same regardless whether the antenna is used to transmit or receive.

GigaHertz (GHz) is one billion hertz, which is a frequency measurement.

The Global Positioning System (GPS) is a "constellation" of 24 satellites that orbit the Earth at a height of 10,900 miles, making it possible for people using ground receivers to determine their geographic location within 10 to 100 metres. The satellites use simple mathematical calculations to broadcast information that is translated as longitude, latitude and altitude by Earth-based receivers.

A man-made system of conductors placed below an antenna to serve as an earth ground

Antenna measurements in general and radiation patterns in particular must be performed with polarisation in mind. Since polarisation is defined as having the same orientation as an antenna’s electric field vector, it is common practice to refer to measurements aligned with either the electric vector ( E-plane) or magnetic vector (H-plane).

Height Above Average Terrain (HAAT) is a measure of an antenna's height above average terrain. This value is used by the FCC in determining compliance with height limitations and transmitting powers for high sites.

A centerfed antenna whose electrical length is half the wavelength of the transmitter or received signal. An antenna consisting of two rods (1/4 wave­length each) in a straight line, that radiates electromagnetic energy.

An antenna with a spiral conductor wound around a cross section. An antenna that has the form of a helix.

Hertz(Hz) is the measure of frequency which means cycles per second.

High-gain Antenna is a type of antenna that significantly increases signal strength. High-gain antennas are necessary for long-range wireless networks.

Public area where wireless LAN Internet access is apt to be used for high-speed access to e-mail, web sites, etc. Users are usually unproductive while waiting. Examples are convention centres, hotels, airports, train stations, bus stations, restaurants and coffee shops.

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.

Link budget is a calculation involving the gain and loss factors associated with the antennas, transmitters, transmission lines and propagation environment. It is used to determine the maximum distance at which a transmitter and receiver can successfully operate.

Microconnect Distributed Antennae (MDA) are small-cell local area (200--300 metre range) transmitter-receivers usually fitted to lampposts and other street furniture in order to provide Wireless LAN, GSM and GPRS connectivity. They are therefore less obtrusive than the usual masts and antennae used for these purposes and meet with less public opposition. Each antenna point contains a 63-65 GHz wireless unit alongside a large memory store providing proxy and cache services.

1 million cycles per second.

Multiple Input Multiple Output (MIMO) refers to the use of multiple antennas in a Wi-Fi device to improve performance and throughput. The MIMO technology takes advantage of a characteristic called multipath, which occurs when a radio transmission starts out at point A and then reflects off or passes through surfaces or objects before arriving, via multiple paths, at point B. MIMO technology uses multiple antennas to collect and organise signals arriving via these paths. The technology is included the 802.11n standard.

Multiple Input Single Output (MISO) is a smart antenna technology that uses multiple transmitters and a single receiver on a wireless device to improve the transmission distance. MISO technology can be applied in areas such as Digital TeleVision (DTV), Wireless Local Area Networks (WLANs), Metropolitan Area Networks (MANs), and mobile communications. The implementation of MISO would include multiple antennas at the source or transmitter, and the destination or receiver has only one antenna. The antennas are combined to minimise errors and optimise data speed. Other forms of smart antenna technology include Multiple Input Multiple Output (MIMO) and Single Input Multiple Output (SIMO).

Refers to any antenna mounted on a vehicle. It Includes a radiating element and a mechanism to fix the antenna to the vehicle.

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.

A mount is the device onto which a mobile antenna attaches. It is the mechanical and electrical interface between an antenna and the vehicle.

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 multipath propagation depends on the type of reflective surface; flat metal, towers and buildings cause the strongest effects.

Noise refers to any undesirable communication channel signals.

Noise figure is a figure of merit for receivers and preamplifiers representing the amount of excess noise added to the signal by the amplifier or receiving system itself. The lower the noise figure, the less excess noise is added to the signal.

An antenna providing a 360-degree transmission pattern. This type of antenna is used when coverage in all directions is required.

Panel Antenna is an antenna type that radiates in only a specific direction. Panel antennas are commonly used for point-to-point situations. You may also see them called "patch antennas."Parabolic Antenna Parabolic Antenna is an antenna type that radiates a very narrow beam in a specific direction. Parabolic antennas offer the highest gain for long-range point-to-point situations.

Printed Circuit Board.

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.

Proportional Fair Scheduling (PFS) is a scheme for wireless communication for a single antenna system and multiple transmit and receive antennas. The Proportional Fair algorithm is an algorithm that schedules the channel for the station that has the maximum of the priority function. Where T denotes the data rate potentially achievable for the station in the present time slot and R is the historical average data rate of this station. Parameters α and β tune the fairness of the scheduler, that is, is it fair to all stations giving them equal bandwidth or is the scheduler maximising the throughput of the channel.

An antenna in which all of the elements, both active and parasitic, are in one plane.

A term used to describe Ethernet cable that has a slow-burning, fire-resistant casing which emits little smoke. Plenum-rated Ethernet cable is used in overhead ductwork.

A communications channel running from one point to several other points.

A long-range wireless network between two points. Point-to-point wireless networks use directional antennas.

The sense of the wave radiated by an antenna. This can be horizontal, vertical, elliptical or circular (left or right hand circularity) depending on the design and application.

Polarisation diversity is a diversity technique where antennas of different polarisations, i.e. horizontal and vertical, are used to provide diversity reception. The antennas take advantage of the multipath propagation characteristics to receive separate uncorrelated signals.

All antennas made by means of a printed circuit process.

Propagation is the process an electromagnetic wave undergoes as it is radiated from the antenna and spreads out across the physical terrain. See also propagation channel.

Propagation channel is the physical medium electromagnetic wave propagation between the transmit and receive antennas, and includes everything that influences the propagation between the two antennas.

An antenna with an electrical length that is equal to one-quarter wavelength of the signal being transmitted or received. A half-wave antenna cut in half, with one end grounded.

The graphical representation of the relative field strength radiated from an antenna in a given plane, plotted against the angular distance from a given reference.

A discrete conductor radiating RF energy in an antenna system.

Radio propagation refers to the electromagnetic waves at radio frequencies as they radiate from a transmitting antenna.

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 minimise wind loading.

Receive diversity is the process of providing two independent receiving systems and spatially separated antennas to overcome fading effects on the radio signal.

Receiver is a device on a transmission path which converts the signals as received from the transmission system into the signals required by the destination equipment.

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.

Repeater, also known as network repeater, is a type of network device that regenerates incoming electrical, wireless or optical signals. With physical media such as Ethernet or Wi-Fi, data transmissions can only span a limited distance before the quality of the signal degrades. Repeaters attempt to preserve signal integrity and extend the distance over which data can safely travel. Active hubs are repeaters. In Wi-Fi, access points function as repeaters when operating in so-called "repeater mode." In moble wireless, a repeater receives radio signals from the base station and then amplifies and retransmitts to areas where radio shadow occurs and vice versa.

Radio Frequency generally refers to wireless communications with frequencies below 300 GHz. Formally, according to the Article 2 of th Radio Law, radio frequency is below 3,000 GHz. Radio frequencies can be used for communications between a mobile telephone and an antenna mast.

Radio frequency identification (RFID) is a system for tagging and identifying mobile objects such as store merchandise, postal packages and sometimes living organisms (like pets). RFID uses low-powered radio transmitters to read data stored in a transponder (tag) at distances ranging from one inch to 100 feet. RFID tags are used to track assets, manage inventory and authorize payments, and they increasingly serve as electronic keys for everything from autos to secure facilities. RFID works using small (sometimes smaller than a fingernail) pieces of hardware called RFID chips. These chips feature an antenna to transmit and receive radio signals. So-called passive RFID chips do not have a power source, but active RFID chips do. RFID chips may be attached to objects, or in the case of some passive RFID systems, injected into objects.

The RoHS Directive stands for “the restriction of the use of certain hazardous substances in electrical and electronic equipment”. This Directive baned the placing in the EU market of new electrical and electronic equipment containing more than agreed levels of lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyl (PBB) and polybrominated diphenyl ether (PBDE) flame retardants from 1 July 2006.

Receive/transmit Transition Gap (RTG), a concept in the mobile wireless network, is a gap between the last sample of the uplink burst and the first sample of the subsequent downlink burst at the antenna port of the BS in a time division duplex (TDD) transceiver. This gap allows time for the base station (BS) to switch from receive to transmit mode. During this gap, the BS is not transmitting modulated data but simply allowing the BS transmitter carrier to ramp up, and the transmit/receive (Tx/Rx) antenna switch to actuate.

Space Division (or Diversity) Multiple Access (SDMA), also known as multiple beam frequency reuse, employs spot beam antennas to reuse frequencies by pointing the antenna beams using the same frequency in different directions.

Sector is a coverage area associated with a base station having its own antennas, radio ports and control channels. The concept of sectors was developed to improve co-channel interference in cellular systems, and most wireless systems use three sector cells.

Sector Antenna is an antenna type that radiates in only a specific direction. Multiple sector antennas are commonly used in point-to-multipoint situations.

A measurement of how well the shielding material (braid, solid tape, etc.) protects the external environment from radiation produced by the central conductor.

Signal Booster compensates for loss of effect (weakening of the signal in the coaxial cable) between the outer antenna and the phone. It can apply to both incoming and outgoing signals.

Signal Diversity is a process by which two small dipole antennas are used to send and receive, combining their results for better effect.

Signal loss is the amount of signal strength that's lost in antenna cable, connectors and free space. Signal loss is measured in decibels.

Single Input Multiple Output (SIMO) is a form of smart antenna technology for wireless communications in which a single antenna at the transmitter and multiple antennas are used at the destination (receiver). An early form of SIMO, known as diversity reception, has been used by military, commercial, amateur and shortwave radio operators at frequencies below 30 MHz since the First World War. The other forms of smart antenna technology include Single Input Single Output (SISO), Multiple Input Multiple Output (MIMO) and Multiple Input Single Output (MISO).

Single Input Single Output (SISO) is a form of antenna technology for wireless communications in which a single antenna at both the transmitter and at the destination (receiver) are used.

Spatial Multiplexing (SM) is a transmission technology developed by Stanford University and Iospan Wireless in California exploiting multiple antennas at both the BS and CPE to dramatically increase the bit rate in a wireless radio link with no additional power or bandwidth consumption. Under certain conditions, SM offers linear increase in spectrum efficiency with the number of antennas.

Satellite Master Antenna Television (SMATV) refers to the transmission of television programming to a Satellite Master Antenna installed on top of an apartment building, a hotel, or at another central location from where it serves a private group of viewers. The transmission usually is done in C-band to 1.5 or 2 metre dishes.

Space diversity is a diversity technique widely used in wireless systems since the very beginning. It consists of two receiving antennas physically (spatially) separated to provide de-correlated receiving signals.

The nominal impedance associated with the transmission line and test equipment.

See VSWR.

Space-Time Adaptive Processing (STAP) is a signal processing technique that enhances the ability of radars to detect targets that might otherwise be obscured by clutter or by jamming. To implement STAP requires sampling the radar returns at each element of an antenna array, over a dwell encompassing several pulse repetition intervals. STAP is for applications such as Sensor Craft, Targets Under Trees and space-based radar programmes.

Space Time Block Coding (STBC) is a technique used in wireless communications to transmit multiple copies of a data stream across a number of antennas and to exploit the various received versions of the data to improve the reliability of data-transfer. The fact that transmitted data must traverse a potentially difficult environment with scattering, reflection, refraction and so on, as well as being corrupted by thermal noise in the receiver means that some of the received copies of the data will be "better" than others. This redundancy results in a higher chance of being able to use one or more of the received copies of the data to correctly decode the received signal. In fact, STBC combines all the copies of the received signals in an optimal way to extract as much information from each of them as possible.

Space Time Coding (STC) is a method employed to improve the reliability of data transmission in wireless communication systems using multiple transmit antennas. STCs rely on transmitting multiple, redundant copies of a data stream to the receiver in the hope that at least some of them may survive the physical path between transmission and reception in a good enough state to allow reliable decoding.

Space-Time Trellis Coding (STTC) is a type of space-time coding (STC) used in multiple antenna wireless communications. This scheme transmits multiple, redundant copies of a trellis (or convolutional) code distributed over time and a number of antennas ("space"). These multiple, "diverse" copies of the data are used by the receiver to attempt to reconstruct the actual transmitted data. For an STC to be used, there must be multiple transmit antennas, but only a single receive antenna is required; nevertheless multiple receive antennas are often used since the performance of the system is improved by so doing.

The connecting link allowing the radio frequency energy generated by the radio to be delivered to the antenna.

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.

Transmit/receive Transition Gap (TTG), a concept of mobile wireless networking, is a gap between the last sample of the downlink burst and the first sample of the subsequent uplink burst in a time division duplex (TDD) transceiver. This gap allows time for the base station (BS) to switch from transmit to receive mode. During this gap, the BS is not transmitting modulated data but simply allowing the BS transmitter carrier to ramp down, the transmit/receive (Tx/Rx) antenna switch to actuate and the BS receiver section to activate.

UniDirectional Link Protocol (UDLP) is used by inexpensive receive-only antennas to receive data via satellite.

VSWR of the antenna is the ratio of the maximum to minimum values of voltage in the standing wave pattern appearing along a lossless 50 Ohms transmission line with an antenna as the load. 

VSWR of the antenna is the ratio of the maximum to minimum values of voltage in the standing wave pattern appearing along a lossless 50 Ohms trans­mission line with an antenna as the load.

Wavelength is the length of one complete wave of an alternating or vibrating phenomenon, generally measured from crest to crest or from trough to trough of successive waves.

Yagi Antenna is an antenna type that radiates in a specific direction. Yagi antennas are used only in point-to-point situations.