Glossary

Absorption

Describes the process by which RF energy penetrates a material or substance and gets converted to heat. RF energy of the appropriate frequency will experience severe absorption when it encounters rain.

Adapter

A short, two-sided connector used to join connectors from different families. It is primarily used to connect a cable (with a connector from one family) to a cable or component (with a connector from a different family).

Air interface

A general term used to describe how a wireless signal interfaces with the free space between a cellular phone and a basestation. It usually involves modulating the RF carrier to increase the information carrying capacity of the wireless system. Examples include CDMA, TDMA, and FDMA.

Altimeter

A device which uses radar technology to determine an airplane's altitude by reflecting an RF signal off the ground.

Amplifier

An active RF component used to increase the power of an RF signal. Amplifiers come in three varieties: high power, low noise, and "other." Other includes variable gain amplifiers and limiting amplifiers. Amplifiers are mostly solid state today, but they can also be traveling wave tubes.

Amplitude modulation

A form of modulation which works by superimposing an information signal onto an RF carrier by varying the amplitude of successive sine waves of the carrier.

Analog

An electrical signal which varies over time and can take on any value between its minimum and maximum values.

Antenna

An RF component used to transform an RF signal, traveling on a conductor, into an airborne wave and vice versa. For antennas to work properly, their size must be similar to that of the wavelength of the signal they are intended to radiate. Antennas can be active or passive components.

Antenna pattern

A graphical tool used to show a birds-eye view of the RF energy radiating out from an antenna.

Attenuation

Phenomenon by which an RF signal is made smaller as it moves from one point to another. It is used interchangeably with the term insertion loss and it is measured in decibels.

Attenuator

An RF component used to make RF signals smaller by a predetermined amount, which is measured in decibels. There are two general categories of attenuators: fixed and variable. Fixed attenuators are also referred to as pads. There are two categories of variable attenuators: voltage variable attenuators and digital attenuators.

Balanced amplifier

An amplifier configuration which combines two amplifiers in parallel to provide redundancy and improved match.

Bandwidth

A measure of the usable frequency range of a component or application. It equals the difference between the upper frequency and the lower frequency and can be expressed in Hertz or as a percentage.

Baseband

The lowest frequency signal in a transmitter or receiver. It is the modulated RF signal after it is fully downconverted in a receiver or before it is upconverted in a transmitter.

Basestation

The wireless access point of a cellular system. It consists of all the necessary infrastructure to enable wireless communications including a tower, antennas, cables, RF transceivers, and power supplies. It is also referred to as a cell site.

Beamwidth

An angular measure, in degrees (of a circle), used to describe the width of the RF energy radiated from an antenna. It is also a measure of the width of an antenna pattern.

Bidirectional

Any RF component which works equally well in both directions. It can also be referred to as dual-directional. Antennas are almost always bi-directional while amplifiers are never so.

Broadband

Used to describe a characteristic of an RF component or wireless application with a "wide" bandwidth. It is also referred to as wideband. A rule of thumb is that any bandwidth greater than 50% is considered broadband.

Broadcasting

An RF system in which a single transmitter is used to communicate with a multitude of geographically dispersed receivers.

Cable assembly

A combination of bulk coaxial cable with coaxial connectors attached to each end.

Capacitor

A small, passive component used to shape electrical signals, found in every electrical circuit.

Carrier

An RF signal-ideally a perfect sine wave-which has an information signal superimposed upon it, through modulation, to carry it as a wave over the air.

Cavity

A family of RF components made by utilizing uniquely constructed hollow metal containers. Cavity components are primarily used for high power applications.

Cell site

See Basestations.

Cellular

A general term used to describe any one of several mobile wireless telephony applications which divide up a given geographical area into smaller subregions called cells.

Channel

A frequency subdivision of a bandwidth. Most RF applications divide their allocated bandwidth into different channels.

Circuit

An organized interconnection of passive and active electrical components to accomplish some electrical objective. A circuit can be further described as analog, digital, or RF, depending on the application.

Circulator

A three-port, passive RF device made of magnets and ferrite material which is used to control the direction of signal flow in an RF circuit.

Coaxial cable

Media used to transport an RF signal. It is comprised of an inner conductor (wire) surrounded by dielectric material (insulator) and covered by an outer conductor (shield). It is frequently referred to by its "RG" number.

Code division multiple access

A type of air interface which describes a technique of adding signal carrying capacity to a given bandwidth by allowing multiple signals to occupy the same frequency at the same time, and assigning each one the unique "address" of the intended receiver. It is also used to describe a form of direct sequence spread spectrum.

Collision avoidance

A radar system mounted on the front of an automobile which is used to determine the appropriate driving distance from the car in front. It is also used on airplanes.

Combiner

A passive RF device used to add together, in equal proportion, two or more RF signals.

Component

Any object an electrical signal encounters in a circuit. Used interchangeably with the term device, all components are either active or passive.

Connector

A cylindrical, metallic object firmly attached to a cable or component which is used to facilitate joining one to the other. It is also referred to as a coaxial connector.

Continuous wave

Any RF signal which is never turned off. It is primarily used to describe a type of radar in which the transmitter is always on.

Continuous wave radar

A type of radar in which the transmitted signal is always on. See also Doppler radar.

Conversion loss

The insertion loss a signal experiences in a mixer as it goes from the RF port to the IF port or vice versa. It is measured in decibels.

Coupler

A passive RF component in which the input signal is split unevenly and the smaller one is siphoned off to be used somewhere else in the system. This type of coupler can be directional or bidirectional. There is another type of coupler called a Lange or quadrature (or quad) coupler in which the signal is split evenly between two ports, but one of the outputs is phase-shifted from the other. Quad couplers are also referred to as quad hybrids.

Current

Electrons on the move, either on a conductor or inside a component.

Decade

A bandwidth in which the highest frequency is 10 times bigger than the lowest frequency.

Decibel

A mathematical conversion, utilizing logarithms of a ratio, which is used as a unit of measure for RF signals. It is primarily used as a measure of the (power) gain and (insertion) loss of RF components.

Demodulation

The process of separating the RF carrier from the information signal in a modulated signal.

Demodulator

An RF device used to perform demodulation. It is a complex component which is comprised of active and passive devices, especially mixers.

Detector

A passive RF component used to convert an RF power signal into a voltage signal. It is used to supply a voltage, which is proportional to the RF power signal, to another component or piece of test equipment which is not designed to handle an RF power signal.

Device

See Component.

Dielectric

Any material which does not conduct electricity (an insulator). When used in the context of RF, dielectric material is a special type of insulator which is designed to minimize the insertion loss of an RF signal being carried on a conductor attached to it.

Digital

An electrical signal which varies over time and can take on only one of two values: high and low.

Digital signal processing

Describes the process of using sophisticated mathematical computations and signal processing to pack a lot of information into a digital signal.

Diode

A semiconductor device used in many RF components. There are several different types of RF diodes which are each manufactured differently to optimize different performance parameters.

Diplexer

See Duplexer.

Direct broadcast satellite

A high power, geosynchronous orbit satellite which transmits broadcast signals to be received by small antenna dishes attached to the home.

Direct sequence spread spectrum

A spread spectrum technique which involves "imprinting" a special digital code onto the RF carrier so that only the intended receiver can decipher it.

Directional coupler

A coupler which only works in one direction.

Discrete component

An electrical component which performs a single function and is housed in its own package.

Distributed circuit

A type of RF circuit philosophy in which some passive components are made from uniquely shaped circuit traces.

Divider

A passive RF device which equally divides an RF signal into two or more RF signals.

Doppler radar

A type of radar which utilizes the return signal's frequency shift to determine an object's velocity.

Downconverter

Another name for a mixer in a receiver; it is used to lower the frequency of the RF signal.

Downlink

The path an RF signal travels from a satellite to the ground.

Dual directional coupler

A coupler which works equally well in both directions.

Dual mode

Describes mobile phones which can communicate in both first generation cellular (analog) and second generation cellular (digital) modes.

Duplex

Describes an RF system which has the ability to transmit and receive simultaneously. Used most frequently with regard to telephony.

Duplexer

A passive RF device which contains two bandpass filters with different passbands. It is also called a diplexer.

Dynamic range

A measure of how large a signal an RF component can handle without distorting it. It is the key performance parameter of any device operating in a digital wireless system. One measure of a component's dynamic range is its third order intercept point, measured in dBm. Sometimes the dynamic range is specified as a combination of a component's third order intercept and its noise figure. The term is often used interchangeably with the term linearity.

Earth station

The name given to the ground facilities which communicate with a satellite.

Effective isotropic radiated power

Describes the amount of RF energy from a satellite which reaches the Earth within the satellite antenna's footprint.

Electronically scanned array

An antenna, made up of many small transceivers, which can sweep an antenna pattern without moving anything mechanically.

Feedback

An electrical circuit technique whereby a signal at one point in the system is sampled and "fed back" to a prior point in the system and used to make adjustments or corrections.

Ferrite

A composite material with excellent magnetic properties used to make isolators, circulators, and transformers.

Filter

A passive RF component which passes or rejects a signal solely on the basis of its frequency. There are four main categories of filters: low pass, high pass, bandpass, and band reject.

Fire control radar

A type of radar system, used in fighter aircraft, to control the targeting of a missile.

Footprint

The antenna pattern which the antenna on a satellite projects onto the Earth.

Frequency

The measure of how many complete sine wave cycles occur in one second in an RF signal, measured in Hertz.

Frequency division multiple access

A type of air interface which describes a technique of adding signal carrying capacity to a given bandwidth by dividing it up into smaller frequency bands.

Frequency hopping spread spectrum

A spread spectrum technique which involves constantly changing the RF carrier's frequency in such a way that only the intended receiver can decipher it.

Frequency modulation

A form of modulation which works by superimposing an information signal onto an RF carrier by varying the frequency of successive sine waves of the carrier.

Frequency response

A graph of amplitude gain or loss, versus frequency, for an RF component. It is used to describe how the particular component behaves as the signal's frequency changes.

Frequency reuse

Describes the unique feature of mobile wireless telephone services in which more than one party can use the same exact frequency, at the same time, in a given geographical location.

Gain

The increase in size of the output signal of an amplifier with respect to the input signal. It is measured in decibels.

Gallium Arsenide

A compound semiconductor material, made of gallium and arsenic, used to make RF diodes and transistors. It is the preferred semiconductor material of choice for very high frequency RF products.

Geostationary orbit

See Geosynchronous orbit.

Geosynchronous orbit

An orbit, 22,000 miles above Earth, in which satellites rotate around the Earth at the same speed as the Earth's rotation, giving them the appearance of not moving.

Global positioning system

A system of 21 satellites which continuously transmit special signals used by special receivers to determine location.

Handoff

Describes the process whereby a mobile telephone call is transferred from one cell site to another with no interruption of service.

Hertz

The unit of measure for frequency, it measures a signal's "cycles per second."

Hybrid

When used in the context of circuit technologies, it describes an RF circuit made by combining chips and discrete components onto a ceramic substrate, which is also referred to as a microwave integrated circuit (MIC). When used in the context of coupling, it describes a Lange coupler.

Impedance

A measure of an RF component's input and output "size," expressed in ohms. In RF systems, the standard size used by all components is 50 ohms.

Impedance matching

The process of converting the output impedance of some RF device-which is not 50 ohms-to 50 ohms, so that it can be operatively connected to some other component.

Impedance ratio

A number used to quantify a transformer's ability to convert one impedance value to another. A transformer with a two-to-one (2:1) impedance ratio can convert a 100 ohm impedance to 50 ohms.

Inductor

A small, passive component used to shape electrical signals, made by winding a wire into a spiral. It is found in most electrical circuits.

Insertion loss

A measure of how much smaller the output signal of a passive device is with respect to the input signal. It is measured in decibels.

Insulator

Any material which does not conduct electricity.

Integrated circuit

Combining more than one active and/or passive device onto a single piece of semiconductor material.

Intercept point

See Third order intercept.

Intermediate frequency

The name of the signal between the two mixers in a two mixer receiver. It is also used to identify one of the ports of a mixer.

Isolation

A measure of the insertion loss in the "open" path of an RF switch, or between any two ports in a passive RF component. Like insertion loss, it is measured in decibels.

Isolator

A two-port passive RF device made of magnets and ferrite material which is used to protect other RF components from excessive signal reflection. Isolators are circulators in which the third port is connected to a heat dissipating load.

Lange coupler

See Coupler.

Limiting amplifier

An amplifier which is used to protect the RF device which comes after it by limiting its output power to a predetermined level, regardless of the input power.

Linearity

See Dynamic range.

Local loop

The telephone circuit from the home (or office) to the local telephone company and back.

Local multipoint distribution service

A fixed wireless application operating around 28 GHz which is ideally suited for wireless local loop service.

Local oscillator

An RF component which produces a perfect sine wave signal; it is connected to one of the ports of a mixer.

Loss

A measure of the decrease in size of an output signal from a passive component, with respect to the input signal. It is measured in decibels.

Lumped element circuit

A type of RF circuit philosophy which utilizes packaged passive components.

Macrocell

The family of cell sites with the greatest signal carrying capacity. They require relatively high power RF transmission.

Match

A measure of how perfectly two RF components "fit" together, which results in less of the RF signal between them being reflected. Match is measured by VSWR, which is expressed as a ratio of X:1, and by return loss, which is measured in decibels.

Microcell

The family of cell sites which results from subdividing macrocells. They require a relatively moderate amount of transmitted RF power.

Microwave

A term loosely used to describe a range of frequencies between 1 and 40 GHz.

Microwave integrated circuit

See Hybrid.

Millimeter wave

A term loosely used to describe a range of frequencies greater than 40 GHz.

Mixer

A three-port RF component used to change the frequency of one of the input signals. It is sometimes referred to as an upconverter (in a transmitter) or a downconverter (in a receiver). Mixers can be active or passive devices, although most are passive.

Mobile switching center

The central communications hub of a cellular telephone system which is responsible for routing all the calls from the various basestations to other basestations or to the public switched telephone network, and for billing. It is also referred to as the mobile telephone switching office.

Mobile telephone switching office

See Mobile switching center.

Modulation

Superimposing an information signal onto an RF carrier by varying some aspect of the carrier. There are three fundamental types of modulation: amplitude modulation, phase modulation, and frequency modulation.

Modulator

A device which superimposes an information signal onto an RF carrier. It has two inputs (the carrier and the information signal) and one output (the modulated signal).

Monolithic microwave integrated circuit

An integrated circuit designed for RF purposes. It can be made of several different semiconductor materials, but the two most common are silicon and gallium arsenide.

Multipath

The phenomenon in which a single wireless signal takes two different paths to the intended receiver.

Narrowband

Used to describe a characteristic of an RF component or wireless application with a "narrow" bandwidth. A rule of thumb is that any bandwidth less than 50% is considered narrowband.

Noise

Any unwanted changes to an RF signal. Noise usually manifests itself as unwanted changes in the sine wave's amplitude, referred to as AM noise, although FM noise is also possible. Mixers are notorious for injecting noise onto an RF signal.

Noise figure

A measure of how much noise an RF component injects onto an RF signal. Noise figure, which is measured in decibels, is most often mentioned with regard to low noise amplifiers.

Octave

Describes a bandwidth in which the highest frequency is twice as big as the lowest frequency.

Omnidirectional

Describes an antenna which radiates RF energy out equally in all directions.

Oscillator

An active RF component with a sole purpose to produce a perfect sine wave at a predetermined frequency. It is also referred to as a source.

Pad

A fixed attenuator (its insertion loss is constant).

Passband

The frequency range of a bandpass filter which has low insertion loss and therefore allows the signal to pass. A passband is defined by identifying its upper and lower frequency.

Personal communication services

Second generation (digital) cellular services in the United States.

Phase locked loop

An oscillator which incorporates feedback in an effort to produce a more perfect sine wave. A phase locked loop can be part of a very sophisticated oscillator called a synthesizer.

Phase modulation

A form of modulation which works by superimposing an information signal onto an RF carrier by varying the phase of successive sine waves of the carrier.

Picocell

The smallest family of cell sites. They provide for the least signal-carrying capacity, cover the smallest area, and require the lowest amount of transmitted RF power.

Polarization

Refers to the fact that RF sine waves have spatial orientation to them as they travel in the air. The three types of polarization are horizontal, vertical, and circular.

Power divider

See Divider.

Printed circuit board

Describes a circuit technology in which metal traces are mounted on a plastic composite material which is used to interconnect electrical components. The motherboard inside a personal computer uses a printed circuit board.

Propagation delay

The time it takes for a signal to travel from the Earth to a satellite and back again. For satellites in geosynchronous orbit, the delay is about a quarter of a second.

Quadrature (Quad) coupler

See Coupler.

Quadrature (Quad) hybrid

See Coupler.

Radar

A wireless system which uses reflected RF energy to detect an object's range, location, and velocity.

Radar cross section

The effective area to reflect RF energy of a object being sensed by radar.

Radiate

A term used to describe the process by which an RF signal changes into an airborne wave.

Radio frequency

Shame on you. Used to identify a class of high frequency electrical signals intended to be radiated as waves. It is also used to describe a range of frequencies less than 1 GHz.

Receiver

One of the two main building blocks of a wireless system which is responsible for collecting the RF energy from the antenna and reducing the signal's frequency down to where it can be accepted by the demodulator.

Reflection

A term used to describe an RF signal's behavior when it encounters an impedance mismatch or a solid object. With an impedance mismatch, some (or all) of the RF energy is reflected back in the direction from which it came. With a solid object, the RF energy bounces off the object at the same angle at which it encountered it.

Repeater

A general term used to describe an RF system which is designed to geographically extend the RF coverage of a macrocell.

Resistor

A small, passive component used to reduce the size of electrical signals, it is found in every electrical circuit.

Return loss

A measure of match between two RF components, expressed in decibels. The better the match, the less energy reflected, the higher the return loss.

Saturation

The behavior of all amplifiers when the input power exceeds a certain point; the amplifier no longer amplifies and the output is more or less constant. When an amplifier is in the saturated region, it said to be nonlinear and causes distortion to the RF signal.

Scanning

Electrically or mechanically moving a radar's antenna pattern to achieve radar coverage over a large area.

Self-resonant frequency

The frequency at which an object will oscillate if sufficiently excited by electrical energy. Almost all solid objects have a self-resonant frequency.

Signal

Electrical energy which is made to vary, over time, in a controlled manner.

Silicon

A semiconductor material used to make RF diodes and transistors. Because it is low cost, it is the preferred material choice for low frequency RF products.

Skin effect

A term used to describe an RF signal's behavior when it is on a conductor. Because of their high frequency, RF signals do not penetrate into solid conductors, but rather exist exclusively on the outer surface.

Source

See Oscillator.

Specialized mobile radio

A cellularlike service in the United States which combines standard cellular operation with dispatch capability.

Spectrum

A term used to describe a range of frequencies for a specific application.

Spread spectrum

A digital modulation scheme which increases the signal carrying capacity of a given bandwidth by allowing multiple signals to occupy the same frequency and distinguishing each one by its unique "address." The modulation process causes each signal's bandwidth to increase.

Station keeping

The practice, by satellites, of using small bursts of propellant to change position to ensure that they do not stray very far from their intended location in geosynchronous orbit.

Stopband

The frequency range of a band reject filter which has high insertion loss and therefore stops signals from passing. A stopband is defined by identifying its upper and lower frequency.

Subassembly

See subsystem.

Subsystem

An RF item, in a single container, which performs more than one function and utilizes more than one component. For example, a combination of a mixer, a filter and an amplifier in a single box is considered a subsystem.

Surface acoustic wave

An electrical signal converted to a sound wave. In surface acoustic wave devices, the sound wave travels along the surface of the device, rather than inside of it.

Switch

An active RF component which switches a single input between one or more outputs. RF switches are characterized by their number of poles (switches) and throws (outputs).

Synthesizer

A very sophisticated oscillator incorporating other electronic circuitry, plus feedback, to make a more perfect sine wave.

T/R switch

A single-pole, double-throw switch situated between a transmitter, a receiver, and an antenna.

Thermal impedance

A measure of how hot a component gets for a given amount of power dissipated. It is expressed in °C/watt.

Third order intercept

The measure of an RF component's linearity or dynamic range, expressed in dBm. It is also referred to as the intercept point. The higher the measure, the more linear the component and the less distortion of the RF signal.

Time division multiple access

A type of air interface which describes a technique of adding signal carrying capacity by breaking up each frequency allocation into multiple time slots and assigning each signal a specific slot.

Trace

A small, thin piece of metal on a dielectric material used to carry signals.

Transceiver

A combination transmitter and receiver in a single package.

Transfer curve

A graph of output power versus input power of an amplifier.

Transformer

A passive RF component used in impedance matching, among other things. It is defined by its impedance ratio.

Transistor

A semiconductor device utilized primarily in amplifiers to create gain; they can also be used by other RF components to perform switching. There are many different varieties of transistors which are made from different semiconductor materials.

Transmitter

One of the two main building blocks in a wireless system which is responsible for taking the signal from the modulator, increasing its frequency and power, then radiating it out the antenna.

Transponder

An RF subsystem onboard a satellite which is responsible for receiving the uplink signal, converting it to the downlink frequency, and then retransmitting it.

Traveling wave tube

An older technology RF amplifier which amplifies RF signals in a vacuum, inside a cavity.

Triangulation

A method for determining position by receiving three different wireless signals from three different locations.

Triplexer

A passive RF device which contains three bandpass filters with different passbands.

Tuner

An RF device, used in a receiver, to frequency-select individual channels.

Upconverter

Another name for a mixer used in a transmitter which is used to raise the frequency of the RF signal.

Uplink

The path an RF signal travels from the ground to a satellite.

Varactor

A diode used to vary the frequency in a voltage-controlled oscillator.

Variable gain amplifier

An amplifier with an external control which is used to vary its gain.

Very small aperture terminal

An RF system in which many small Earth stations use a satellite to communicate with a single receiver.

Voltage

Electrical potential. There are two types: AC (alternating), like the kind in a wall outlet, and DC (direct), like the kind in a battery.

Voltage-controlled oscillator

An oscillator with an external control which is used to vary its output frequency.

Voltage standing wave ratio

A measure of match between two RF components, expressed as a ratio of X:1. The lower the X, the better the match.

Watts

Unit of measure for any kind of power, e.g., RF, heat, etc.

Waveguide

Pipes, with rectangular cross sections, used to carry RF signals from one point to another. Inside, the RF signals move as waves and the waveguide serves to guide and control their movement.

Wavelength

A measure of the length of an RF signal. The higher a signal's frequency, the shorter its wavelength.

Wideband

See broadband.

Wireless

A marketing term generally used to describe the newer RF applications.

Wireless local area networks

A local area network of computers which communicate via wireless signals.

Wireless local loop

An RF system which allows wireless communication with the local telephone company.