In our industry there are a number of terms that are used and below is a list of some of the common abbreviations that we come across followed by a brief description.
Quantities and units used to characterise electromagnetic radiation
Frequency – hertz – Hz
Wavelength – metre – m
Electric field strength – volt per metre – V/m
Magnetic field strength* – ampere per metre – A/m
Magnetic field, – B/Magnetic flux density*– tesla T
Intensity/Power – density watt per square metre – W/m2
Specific energy absorption rate (SAR) watt per kilogram W/kg
The reduction of RF power through a device, usually measured in decibels (dB), and given mathematically by Attenuation (dB) = 10 log (Pout/Pin).
Band Reject Filter
A filter that rejects one band of frequencies and passes both higher and lower frequencies. Sometimes called a notch filter.
Band Reject (Notch) Filter
A filter that rejects one band of frequencies and passes both higher and lower frequencies.
The width of the passband of a bandpass filter. This is usually expressed as the frequency difference between lower and upper relative 3dB points.
Beam width In a plane containing the main beam of the antenna, the beam width is the angle between the two directions in that plane in which the radiation intensity is some fraction (usually one half or 3dB) of the maximum value of the main beam intensity.
The signal that carries the information encoded or modulated on it. Typically, the carrier is a fixed frequency sine wave, which may be amplitude-, phase-, or frequency modulated. In advanced forms of telecommunication systems, the carrier may be a moving signal, called a spread spectrum. As long as the characteristics of the carrier signal are deterministic and known by the receiver, virtually any type of carrier signal may be used.
CDNs - Coupling/Decoupling Networks
Decoupling networks are used to ensure that the disturbance signal does not influence the auxiliary equipment and are placed between the EUT and the auxiliary equipment.
A transmission line consisting of two concentric conductors insulated from each other. In its flexible form it consists of either a solid or stranded center conductor surrounded by a dielectric. A braid is then woven over the dielectric to form an outer conductor. A protective plastic covering is placed on top of the braid.
A unit used to express the ratio between two power levels existing at two points. Measured as: dB = 10 LOG10 ( P1 / P2 ).
The directivity of a directional coupler is a measure of how well a directional coupler isolates the couples and isolated ports. The higher the directivity, the more accurate the coupler measurements will be.
Dual Directional Coupler
A passive 4 port device where the power enters through the main line from port 1 to port 2 and a fraction of this power is picked up by the coupled port, port 3. A very small fraction is also picked up by port 4, in case of matched load, the smaller this amount of power picked up by port 4, is a measure of a good coupler directivity. If port 2 of the directional coupler is not terminated with the characteristic impedance of the coupler, mismatch load condition, some power will be reflected back to port 1, and is picked up by the isolated port, port 4.
The range, from the minimum, which is at a level 3 dB above the amplifier's internally generated floor, to a maximum input signal level that a component can accept and amplify without distortion.
Equivalent isotopically radiated power. This is the power that would have to be emitted in all directions to produce a particular intensity and so takes account of the transmitter power plus the characteristics of the antenna.
ELF - Extra Low Frequency
Radio waves (electromagnetic radiation) with frequencies in the frequency range from 3 to 30 Hz.
EMC - Electromagnetic Compatibility
The capability of electrical equipment or systems to function acceptably in their electromagnetic environment.
EMF - Electromagnetic Field
EMF meters are used to measure electromagnetic field radiation. Used to measure AC electromagnetic fields.
ESD - Electrostatic Discharge
ESD simulators, guns or generators are used to generate a voltage discharge via air or contact.
A region of the field of an antenna where the angular field distribution is essentially independent of the distance from the antenna. In this region – also called the free space region – the field has a predominantly plane-wave character, i.e., locally uniform distributions of electric field strength and magnetic field strength in planes transverse to the direction of propagation (see Fraunhofer region).
The far-field measurement of the electric field or the magnetic field. Units: V/m, A/m or W/m
Bandpass Filter A filter that passes one band of frequencies and rejects both higher and lower frequencies.
Gain is the ratio of the power output to the power input of the amplifier in db.
A filter which passes high frequencies and rejects low frequencies.
The impedance measured at the input terminal of a filter when it is properly terminated at its output terminal.
The loss of signal caused by a filter being inserted in a circuit. It has many different definitions and is usually measured in db.
LISN - Line Impedance Stabilization Network
A device that is used in conducted and radiated radio-frequency emission and susceptibility tests, as specified in various electromagnetic compatibility (EMC)/EMI test standards.
A filter which passes low frequencies and rejects high frequencies.
A region generally close to an antenna or other radiating structure, in which the electric and magnetic fields do not have a substantially plane-wave character but vary considerably from point to point. The near-field region is further subdivided into the reactive near-field region, which is closest to the radiating structure and contains most or nearly all of the stored energy, and the radiating near-field region where the radiation field dominates the reactive field, but lacks substantial plane-wave character and is complicated in structure.
Near-Field Region, Radiating
That region of the field of an antenna where the power density is not inversely proportional to the distance from the source. It is sometimes called the Fresnel region. In this region the power density increases irregularly with range to a maximum level, then decreases at a near linear rate to the onset of the far-field region. It is convenient and adequate from a personnel-hazard viewpoint to consider the power density in the radiating near field to be constant with range and equal to four times the average power density calculated at the antenna aperture itself. Such a power density profile has proven accurate when compared to measured results.
The is defined as the lowest possible input to a chain or a component, that will produce a detectible output.
NSA - Normalised Site Attenuation
NSA is used to validate test sites for radiated emission measurements, typically over the frequency range of 30 MHz to 1000 MHz.
The amount in percent by which signal exceeds its steady-state output on its initial rise.
Peak Power Density
The maximum instantaneous power density occurring when power is transmitted.
RADHAZ - Radiation Hazards
Typically, in reference to radiation hazards to personnel or ordnance. Meters are available to measure radiation.
The ratio, in dB, of maximum power sent down a transmission line to the power returned toward the source.
RF - Radio Frequency
Oscillation rate of an alternating electric current, voltage or field (magnetic, electric or electromagnetic) in the frequency range from approx. 20 kHz to approx. 300 GHz
SE - Shielding Effectiveness
SE is defined as the ratio of the electromagnetic field intensity measured before and after the shielding material is installed.
The output impedance of the circuit that drives the filter. The impedance of the circuit the filter must work from or be tested in.
The area of frequency where it is desirable to reject or attenuate all signals as much as practical.
A transmission line where the current flows in the conductor centred between two dielectrics on top and bottom of the conductor. Ground is above and below the two dielectrics. Stripline transmission line has even and odd wave modes of propagation travelling with the same phase velocity due to symmetry.
A filter's transfer function determines both its frequency and time domain characteristics that are commonly used in the analysis of systems such as single-input single-output filters.
The response of a system to a change from a steady state. Examples would be the response of a lowpass filter to a very low frequency square wave or a sudden voltage rise or a sudden burst of signal within a passband.
Voltage Standing Wave Ratio (VSWR)
The ratio between the maximum and minimum of standing waves on a transmission time.
Wavelength ( λ )
The wavelength ( λ ) of an electromagnetic wave is related to the frequency (f) and velocity (υ) by the expression υ = fλ. The velocity of an electromagnetic wave in free space is equal to the speed of light, i.e., approximately 3x108m /s (meters per second).