Glossary

Click one of the letters above to advance the page to terms beginning with that letter.

A

Angle of Incidence

The angle measured from a perpendicular axis to the plane of a surface which energy arrives at. "Normal incidence" refers to the perpendicular direction of propagation to the surface. "Grazing Incidence" refers to energy arriving from the direction almost parallel to the surface (high incident angle). Important in the performance of specular absorbers.

Antenna

A device which increases the efficiency of transmission or reception of radio or radar signals into or from a medium. For instance, transmitting and receiving antennas are the same device.

Antenna Directivity

Refers to the angle range over which an antenna enhances the signal level.

Antenna Gain

The ability of an antenna to "magnify" the energy received from the desired direction.

Antenna Pattern

Refers to the variation in radiated field strength (or received signal levels) found as an antenna is rotated. When the antenna is rotated in a horizontal plane, this variation is called the "azimuth antenna pattern." When the rotation is in elevation angle, it is called "elevation antenna pattern."

Attenuation

Loss of energy (i.e. conversion to heat) as radiation passes through a lossy (absorptive) medium (expressed in dB). Function of the properties of the medium. In contrast to insertion loss or reflectivity.

B

Broad Band Absorber

Wide range of frequencies. Broad band absorbers are useful over a wide range of frequencies. The thickness of the absorber determines the lowest frequency at which it is effective.

C

Coaxial Line

A pipe (so called outer conductor) with a concentric wire (inner conductor) that is used to carry microwave energy with little loss of power.

Compatibility

Refers to the problem of a transmitter on a device causing interference to a receiver, or receivers on the same device (such as may be encountered on satellites, aircraft, or automotive vehicles).

Conductivity Gradient

An absorber in which the dielectric properties effectively vary as the radiation passes through the absorber. This is accomplished by stacking layers having different dielectric properties ( Eccosorb AN, ANW).

D

dB Down

The portion of incident energy which is reflected from a surface. A flat metal surface reflects all incident radiation. Measured in dB which is a logarithmic measure of the portion of energy reflected as compared to that reflected from a flat metal plate of the same area. A metal plate has a reflectivity of 0 dB down. A material which reflects half of the incident energy is 3 dB down or has a reflectivity of -3 dB. A material which reflects one tenth of the incident energy has a reflectivity of -10 dB Reflectivity (%) dB down. For flat sheet absorbers, 20 dB down is generally the best possible and desired performance.

Decibel

A logarithmic ratio (base 10) between two quantities denoted as ""dB."" In terms of energy reflection: dB = 10 x LOG(power reflected/power reflected by metal plate) e.g. dB = 10 x LOG(1/2) = -3 (50% reflected power)

Die Cut

Die cutting is the term used to define the process of cutting material from a larger sheet into the desired shape and size. This is done using a die, a press, and material. The die consists of a die board, usually made from plywood, and steel rule, which is inserted into the die board in the desired configuration. The resulting die is put into a press in such a way that the sharp edges of the die penetrate through the material and cut it out of a larger sheet into the shape made with the steel rule.

Dielectric

A medium through which electric attraction or repulsion may be sustained - an insulator.

Dielectric Constant

The ratio of the capacitance (ability to store electrical energy) of a condenser filled with the material in question to that of the same condenser filled with vacuum.

Dielectric Loss

The power loss in a dielectric due to heating as a wave passes through it. It can be expressed as "dielectric loss tangent" (power factor) or "loss factor". Low loss makes a good dielectric (Eccostock) dielectric materials). High loss is an absorber (Eccosorb), poor dielectric.

Dielectric Materials

Materials which store and/or dissipate electric and/or magnetic energy. Our Eccostock product range.

Dipole Antenna
A metal rod which is a particularly effective antenna at a frequency whose wavelength is twice the length of the rod.

E

Electromagnetic

Phenomenon related to the propagation of electric and magnetic energy. Defined by frequency in the Electromagnetic Spectrum. Electric and Magnetic energy is coupled. Meaning you cannot have one without the other. Described as Electromagnetic fields.

Electromagnetic Compatibility

Refers to the problem of a transmitter on a device causing interference to a receiver, or receivers on the same device (such as may be encountered on satellites, aircraft, or automotive vehicles).

Electromagnetic Fields

A vector field of Electromagnetic energy. The Magnetic (H) and Electric (E) fields generated by any system of electric charges. A low current, high voltage, source will generate mainly an Electric Field. A high current, low voltage, source will generate mainly a Magnetic Field.

Electromagnetic Waves

An electromagnetic wave can be thought of as propagating electric and magnetic fields. An electromagnetic wave propagates with the electric field and magnetic field perpendicular to each other.

EMC

Refers to the problem of a transmitter on a device causing interference to a receiver, or receivers on the same device (such as may be encountered on satellites, aircraft, or automotive vehicles).

F

Far Field

The region where Antenna patterns and RCS patterns need to be measured with adequate transmission distance (in terms of wavelength) or they will not be typical of the patterns expected in typical use over long distances. Measurements made over short distances (near field) contain errors because the fields are curved rather than planar.

Flared Waveguide

A system for measurement of the reflection properties of absorbers at low frequencies. Measurement is made by mounting six pieces for test at one end of a long metal waveguide and determining reflections from the surfaces to the microwave fields at the other end. Emerson &Cuming Microwave Products has four such systems, the largest having a length of 90-ft.

Free Space

Refers to the medium of air (or vacuum) in which radio waves may travel. This is in contrast to waves traveling on transmission lines such as coax or waveguide, or through a medium, such as a Free Space Absorber (Specular Absorber)

Frequency

"The number of cycles per second. Units: Hertz (Hz) 1-cycle. KiloHertz (1000 cycles), MegaHertz (106 cycles), GigaHertz (109 cycles) We are primarily concerned with frequencies of ""short wave"" i.e. VHF ""Very High Frequencies"" 30 - 300 MHz UHF ""Ultra High Frequencies"" 300 - 3,000 MHz SHF ""Super High Frequencies"" 3 GHz - 30.GHz EHF ""Extremely High Frequencies"" 30 - 300 GHz Other common descriptions: Microwaves 1-30 GHz, Millimeter Wave 30-300 GHz"

G

Graded Absorber

An absorber in which the dielectric properties effectively vary as the radiation passes through the absorber. This is accomplished by stacking layers having different dielectric properties (ECCOSORB AN, ANW).

H

Harmonic

A signal present in a complex period waveform which is a multiple of the fundamental frequency, i.e. l st harmonic 2f, 2nd Harmonic 3f.

Hermetic Seal

An airtight seal

I

Impedance

The ratio of electric to magnetic field (E/H) With waves, we speak of "WAVE IMPEDANCE." The wave impedance depends on the distance from the source. In the far field, the wave is known as a plane wave and its impedance is equal to the impedance of free space 377 ohm. In the near field , the wave impedance is determined by the characteristics of the source. In terms of a medium, impedance is the quality of a material which can be calculated from its magnetic and dielectric properties. The closer the values of the impedance of two materials, the less reflectivity will occur at their boundaries. If there is an impedance match there will be no reflectivity.

Insertion Loss

IL - Ratio of input power to transmitted power. Loss of power passing through a material which includes reflection and attenuation.

Isocyanate

Toluene diisocyanate (TDI) is an aromatic hydrocarbon. It is produced for reaction with polyols to form polyurethanes and its vapors should be avoided.

K

Kiss-Cut

Kiss cutting delivers precision cuts through a top layer of material (absorber and adhesive) without cutting the bottom release liner, such as a sheet of stickers. This is commonly used when cutting several different parts and the customer wishes to keep all of the parts together on one sheet or as a set.

L

LNB's

A low-noise block converter is used in communications satellite reception. The job of the LNB is to use the superheterodyne principle to take a wide band of relatively high frequencies, amplify and convert them to similar signals carried at a much lower frequency (called intermediate frequency or IF). These lower frequencies travel through cables with much less attenuation of the signal, so there is much more signal left on the satellite receiver end of the cable

Log Periodic Antenna

This is an antenna based on parallel wire or tubular elements which can effectively radiate energy in a particular direction over a broad range of frequencies.

Lossy

The ability of a material to attenuate or absorb energy. Based on either the dielectric or magnetic properties of the material

Low Noise Block

A low-noise block converter is used in communications satellite reception. The job of the LNB is to use the superheterodyne principle to take a wide band of relatively high frequencies, amplify and convert them to similar signals carried at a much lower frequency (called intermediate frequency or IF). These lower frequencies travel through cables with much less attenuation of the signal, so there is much more signal left on the satellite receiver end of the cable.

M

Microwave

Common usage of electromagnetic waves that refers to the frequency range of 700 MHz to 40 GHz in the electromagnetic spectrum.

MIP

MIP or Mold-in-Place technology is the process of auto-dispensing custom designed flow in place absorbers directly into a customer supplied housing.

Mold-in-Place

MIP or Mold-in-Place technology is the process of auto-dispensing custom designed flow in place absorbers directly into a customer supplied housing.

N

Narrow Band Absorber

Generally a thin single layer absorber which resonates at a specified frequency (e.g. Eccosorb SF)

Near Field

Antenna patterns measured with too short a transmission length contain errors, because the fields in "near field" are curved rather than planar.

NRL Arch

Is the standard system for measurement of reflection properties of absorber at high frequencies. It involves bouncing microwaves from a metal plate and determining reflection properties by alternately covering and uncovering the metal plate with the absorber piece under test. The difference in signal level between these two conditions indicates the absorption capability of that absorber.

O

Outdoor Range

An outdoor range is the alternative to an anechoic chamber. It involves making measurements outdoors instead of indoors. Measurements made on an outdoor range however, are compromised by reflections from the ground and nearby structures which limit measurement accuracy. Such ranges often have the quiet zone within an anechoic chamber to improve such accuracy.

P

Parabolic Dish Antenna

A common microwave antenna in the shape of a parabola. This shape is effective in collecting energy into a narrow beam.

Patch Antenna

A patch antenna is a narrowband, wide-beam antenna fabricated by etching the antenna element pattern in metal trace bonded to an insulating substrate. Some patch antennas eschew a substrate and suspend a metal patch in air above a ground plane using dielectric spacers; the resulting structure is less robust but provides better bandwidth.

Permeability

Measure of the magnetic characteristics of a material. A measure of the effect of a nearby magnet on a material.

Plane Wave

Propagating electromagnetic waves that are equal in magnetic and electric energy. In the far field, all waves propagate as plane waves.

Polarization

The orientation of the electric field of the radiation. Radiation transmitted from a dipole antenna has its electric field parallel to the antenna. The wave travels in a direction perpendicular to the antenna. The electric field of the radiation being transferred is perpendicular to the widest dimension of the rectangle.

Potentiometer

An electrical device which has a user-adjustable resistance

Pulse Radar

In order to permit the use of increased power and reduce the effect of the transmitted wave on the radar receiver, radar signals are often sent out in pulses. Although these pulses are very short in duration they are still made up of many waves. Distance to a target is determined from the time it takes the pulse to reach the target and return.

Q

Q

The ratio of the stored versus transmitted energy. For a capacitor "Q" defines performance. For an enclosure where microwave circuits are operating, Q impedes the performance of a device.

Quality Factor

The ratio of the stored versus transmitted energy. For a capacitor "Q" defines performance. For an enclosure where microwave circuits are operating, Q impedes the performance of a device.

Quiet Zone

This is the region of an anechoic chamber in which the EUT (Equipment Under Test) is to be placed for measurement. Consequently, it is also the region to be measured for demonstration of compliance with reflectivity requirements for the chamber. The quiet zone is most commonly a sphere of diameter large enough to envelop the largest device to be tested. RADAR RAdio Detection AND Ranging. The use of microwaves to transmit and receive information.

R

Radar Cross Section

Refers to the level of signal reflected from the radar target. The term RCS pattern refers to the manner in which a specific target at a specific frequency varies in reflective signal level as the target is rotated.

Radio Frequency Interference

Refers to the problem of a device being susceptible to having its function compromised by interference from nearby high powered transmission.

Radomes

A plastic cap which is sometimes used to cover an antenna to provide weather protection or streamlining. Imperfections of these devices are customarily measured in chambers.

RCS

Refers to the level of signal reflected from the radar target. The term RCS pattern refers to the manner in which a specific target at a specific frequency varies in reflective signal level as the target is rotated.

RCS Reduction

Refers to the degree to which the signal reflected from a radar target is reduced (as a result of absorber treatment or shaping or more likely both). Also known as stealth.

Reflection Coefficient

The ratio of reflected to incident energy.

Reflectivity

The portion of incident energy which is reflected from a surface. A flat metal surface reflects all incident radiation. Measured in dB which is a logarithmic measure of the portion of energy reflected as compared to that reflected from a flat metal plate of the same area. A metal plate has a reflectivity of 0 dB down. A material which reflects half of the incident energy is 3 dB down or has a reflectivity of -3 dB. A material which reflects one tenth of the incident energy has a reflectivity of -10 dB. For flat sheet absorbers, 20 dB down is generally the best possible and desired performance.

Resonance

Cancellation of some or all of the radiation initially reflected from an absorber surface by the portion of the radiation which passes through the absorber. This cancellation is particularly effective when the thickness of the absorber is one quarter of the wavelength of the radiation in the material. In this case the waves leaving the surface of the absorber are said to be "out of phase". Defining principle of Eccosorb SF.

S

Salisbury Screen

Maybe the first ever anti-reflective concept RAM (radar absorbent material). The most easy to understand salisbury screen design consists of a ground plane which is the metallic surface that needs to be concealled, a lossless dielectric of a given thickness (a quarter of the wavelength that will be absorbed) and a thin lossy screen.

Specular Reflections

Reflections from a surface that are based on the geometric properties of a wave (no surface phenomenon). May be thought of as associated with a ray, which arrives I at a surface at a given angle and bounces forward at the same angle (as a ball would bounce or as light would reflect from a mirror). In contrast, with non-specular reflection, a ray striking a surface at an angle reflects off over a wide range of angles with a wide variety of rays.

Speed of Light in a Vacuum

An important universal constant about 3 x 10 pr 300 million meters per second. The speed in other media depend on the dielectric and magnetic properties of the medium. These properties, in turn depend on the frequency of the electromagnetic radiation. In a vacuum all electromagnetic radiation travels at the speed of light.

Standing Wave

If a wave continuously impinges on a surface (CW or continuous wave) a situation often occurs where the voltage at any given point between the transmitter and receiver is constant. This phenomenon is used to determine dielectric and magnetic properties of materials at radar frequencies.

Surface Currents

Traveling and creeping waves which contribute to RCS of an object. They can also contribute to RFI in a microwave module.

Syntactive Foam

Ccomposite materials synthesized by filling a polymer or ceramic matrix with hollow particles called microballoons. The presence of hollow particles results in lower density, higher strength, a lower thermal expansion coefficient, and, in some cases, radar or sonar transparency.

T

Terminations

Lossy slug of material which is used to terminate energy propagation in a waveguide or coxial line with minimum impedance discontinuity

Thermoset

Thermosets are polymer materials that cure, through the addition of energy, to a stronger form by a cross-linking process. A thermoset material cannot be melted and re-shaped after it is cured.

Transition Region

The region around l /6 or approximately one sixth of a wavelength between the near and far fields.

Transmission Length

The distance between the source antenna (sometimes c alled the illuminating antenna or range -antenna) and the Equipment Under Test. The larger the test device, the longer the distance between the source antenna and the device need to be. This minimum distance is often determined from the relationship R=2D2/l , where R is the distance, D refers to the maximum size of the device under test, and l (lambda) is the wavelength.

V

Volume Resistivity

Resistance of a material expressed in terms of volume. Units of ohm-cm. Important parameter of ECCOSHIELD shielding materials

VSAT

Very Small Aperture Terminal (VSAT), is a two-way satellite ground station with a dish antenna that is smaller than 3 meters. VSATs access satellites in geosynchronous orbit to relay data from small remote earth stations to other terminals or master earth station "hubs". VSATs are most commonly used to transmit narrowband data (point of sale transactions such as credit card, polling or RFID data; or SCADA), or broadband data (for the provision of Satellite Internet access to remote locations, VoIP or video). VSATs are also used for transportable, on-the-move (with phased-array antennas) or mobile maritime (such as Vizada or Eutelsat services) communications.

VSWR

The ratio of maximum to minimum of voltage over a single cycle of field variation. Refers to the fact that, with reflections present, fields are periodic, i.e. they vary as a sine wave in intensity. The greater the level of reflection, the greater the so called VSWR (the greater the ratio of maximum to minimum over a single cycle of field variation).

Vulnerability

Refers to the problem of high power radiation causing permanent damage to electronic devices. Important in EMC compliance.

W

Water Jet

Water jet cutting is a process in which a high velocity and high pressure jet of water with or without an abrasive substance is used to slice through metal or other materials. Water Jet cutting is highly precise and generally used for parts requiring greater tolerances than what a steel rule die can offer.

Waveguide

Is a rectangular metal tube used to carry microwave energy with little loss of power. The electric field of the radiation being transferred is perpendicular to the widest dimension of the rectangle. A wave guide is useful over a narrow frequency range.

Wavelengths

The wavelength is the distance between two positive (or negative) peaks. The frequencies that we are primarily concerned with have wavelengths as follows. If one could stop the movement of an electromagnetic wave and measure the voltage at various points along the wave, one would find that it goes through a peak positive value and then drops to a peak negative value At a frequency of 10 GHz (an X-band frequency) this distance is about one inch.

X

XBR

Sea-Based X-Band Radar is a floating, self-propelled, mobile radar station designed to operate in high winds and heavy seas. It is mounted on a 5th generation Norwegian-designed, Russian-built CS-50 semi-submersible twin-hulled oil-drilling platform. Conversion of the platform was carried out at the AMFELS yard in Brownsville, Texas; the radar mount was built and mounted on the platform at the Kiewit yard in Ingleside, Texas, near Corpus Christi. It will be based at Adak Island in Alaska but can roam over the Pacific Ocean to detect incoming ballistic missiles.

Y

Yagi Antenna

This is an antenna based on parallel wire or tubular elements which effectively radiates energy in a particular direction but only a relative narrow range of frequency.