GLOSSARY OF TERMS

ABSORPTION
(1) Absorbing light waves. Does not allow any reflection or refraction; (2) Atmospheric absorption of rf energy with no reflection or refraction (adversely affects long distance communications).

AERIAL
A conductor or set of conductors used either to radiate rf energy into space or to collect rf energy from space.

ANGLE OF INCIDENCE
The angle between the incident wave and the normal.

ANGLE OF REFLECTION
The angle between the reflected wave and the normal.

ANGLE OF REFRACTION
The angle between the normal and the path of a wave through the second medium.

BEVERAGE ANTENNA
A horizontal, long wire antenna designed for reception and transmission of low-frequency, vertically polarized ground waves. Also known as WAVE ANTENNA.

BIDIRECTIONAL ARRAY
An array that radiates in opposite directions along the line of maximum radiation.

An array in which the direction of maximum radiation is perpendicular to the plane containing the elements.

CENTRE-FED
Connecting the centre of an antenna to a transmission line, which is then connected to the final (output) stage of the transmitter. Also known as CURRENT-FED.

CHARACTERISTIC IMPEDANCE
The ratio of voltage to current at any given point on a transmission line. Represented by a value of impedance.

COAXIAL LINE
A type of transmission line that contains two concentric conductors.

COLLINEAR ARRAY
An array with all the elements in a straight line. Maximum radiation is perpendicular to the axis of the elements.

COMBINATION ARRAY
An array system that uses the characteristics of more than one array. Also known as ARRAY OF ARRAYS.

COUNTERPOISE
A network of wire that is connected to a quarter-wave antenna at one end and provides the equivalent of an additional ¼ wavelength.

CRITICAL FREQUENCY
The maximum frequency at which a radio wave can be transmitted vertically and still be refracted back to earth.

CURRENT-FED
See CENTRE-FED.

CURRENT STANDING WAVE RATIO (ISWR)
The ratio of maximum to minimum current along a transmission line.

CUTOFF FREQUENCY
The frequency at which the attenuation of a waveguide increases sharply and below which a travelling wave in a given mode cannot be maintained. A frequency with a half wavelength that is greater than the wide dimension of a waveguide.

CYCLE
One complete alternation of a sine wave that has a maximum value above and a maximum value below the reference line.

DAMPING
Reduction of energy by absorption.

DIELECTRIC HEATING
The heating of an insulating material by placing it in a high frequency electric field.

DIELECTRIC LOSSES
The losses resulting from the heating effect on the dielectric material between conductors.

DIELECTRIC CONSTANT
The ratio of a given dielectric to the dielectric value of a vacuum.

DIFFRACTION
The bending of the paths of waves when the waves meet some form of obstruction.

DIPOLE
A common type of half-wave antenna made from a straight piece of wire cut in half. Each half operates at a quarter wavelength of the output.

DIRECTIONAL.

DIRECTOR
The parasitic element of an array that reinforces energy coming from the driver toward itself.

DIRECTIVITY
The property of an array that causes more radiation to take place in certain directions than in others.

DISTRIBUTED CONSTANTS
The constants of inductance, capacitance, and resistance in a transmission line. The constants are spread along the entire length of the line and cannot be distinguished separately.

DOUBLET
Another name for the dipole antenna.

DRIVEN ARRAY
An array in which all of the elements are driven. Also known as CONNECTED ARRAY

DRIVEN ELEMENT
An element of an antenna (transmitting or receiving) that is connected directly to the transmission line.

A device used at the end of a transmission line or waveguide to convert transmitted energy into heat so no energy is radiated outward or reflected back.

ELECTROMAGNETIC FIELD
The combination of an electric (E) field and a magnetic (H) field.

ELECTROMAGNETIC INTERFERENCE

ELEMENT
A part of an antenna that can be either an active radiator or a parasitic radiator.

END-FED
Connecting one end of an antenna through a capacitor to the final output stage of a transmitter. Also known as VOLTAGE-FED.

END-FIRE ARRAY
An array in which the direction of radiation is parallel to the axis of the array.

ELEVATION ANGLE
The angle between the line of sight to an object and the horizontal plane.

Variations in signal strength by atmospheric conditions.

FEEDER
A transmission line that carries energy to the antenna.

FLAT LINE
A transmission line that has no standing waves. This line requires no special tuning device to transfer maximum power.

FLEXIBLE COAXIAL LINE
coaxial line made with a flexible inner conductor insulated from the outer conductor by a solid, continuous insulating material.

FOLDED DIPOLE
An ordinary half-wave antenna (dipole) that has one or more additional conductors connected across the ends parallel to each other.

FOUR-ELEMENT ARRAY
An array with three parasitic elements and one driven element.

FREE-SPACE LOSS
The loss of energy of a radio wave because of the spreading of the wavefront as it travels from the transmitter.

FREQUENCY
The number of cycles that occur in one second. Usually expressed in Hertz.

FRONT-TO-BACK RATIO
The ratio of the energy radiated in the principal direction to the energy radiated in the opposite direction.

FUNDAMENTAL FREQUENCY
The basic frequency or first harmonic frequency.

GAIN
The ratio between the amount of energy propagated from an antenna that is directional to the energy from the same antenna that would be propagated if the antenna were not directional.

GROUND PLANE
The portion of a ground plane antenna that acts as ground.

GROUND-PLANE ANTENNA
A type of antenna that uses a ground plane as a simulated ground to produce low-angle radiation.

GROUND REFLECTION LOSS
The loss of rf energy each time a radio wave is reflected from the earth’s surface.

GROUND SCREEN
A series of conductors buried below the surface of the earth and arranged in a radial pattern. Used to reduce losses in the ground.

GROUND WAVES
Radio waves that travel near the surface of the earth.

GROUP VELOCITY
The forward progress velocity of a wave front in a waveguide.

HALF-WAVE DIPOLE ANTENNA
An antenna consisting of two rods (¼ wavelength h) in a straight line, that radiates electromagnetic energy.

HARMONIC
A frequency that is a whole number multiple of a smaller base frequency.

HERTZ ANTENNA
A half-wave antenna installed some distance above ground and positioned either vertically or horizontally.

HORIZONTAL AXIS
On a graph, the straight line axis plotted from left to right.

HORIZONTAL PATTERN
The part of a radiation pattern that is radiated in all directions along the horizontal plane.

HORIZONTALLY POLARIZED
Waves that are radiated with their E-field component parallel to the earth’s surface.

INCIDENT WAVE
(1) The wave that strikes the surface of a medium; (2) The wave that travels from the sending end to the receiving end of a transmission line.

INDUCTION FIELD
The electromagnetic field produced about an antenna when current and voltage are present on the same antenna.

INDUCTION LOSSES
The losses that occur when the electromagnetic field around a conductor cuts through a nearby metallic object and induces a current into that object.

INPUT IMPEDANCE
The impedance presented to the transmitter by the transmission line and its load.

INTERFERENCE
Any disturbance that produces an undesirable response or degrades a wave.

IONOSPHERE
The most important region of the atmosphere extending from 31 miles to 250 miles above the earth. Contains four cloud-like layers that affect radio waves.

IONOSPHERIC STORMS
Disturbances in the earth’s magnetic field that make communications practical only at lower frequencies.

IONIZATION
The process of upsetting electrical neutrality.

LEAKAGE CURRENT
The small amount of current that flows between the conductors of a
transmission line through the dielectric.

See LUMPED-IMPEDANCE TUNING.

LOBE
An area of a radiation pattern plotted on a polar-coordinate graph that represents maximum radiation.

LONG-WIRE ANTENNA
An antenna that is a wavelength or more long at its operating frequency.

LONGITUDINAL WAVES
Waves in which the disturbance (back and forth motion) takes place in the direction of propagation. Sometimes called compression waves.

LOOP
(1) The curves of a standing wave or antenna that represent amplitude of current or voltage; (2) A curved conductor that connects the ends of a coaxial cable or other transmission line and projects into a waveguide or resonant cavity for the purpose of injecting or extracting energy.

LOWEST USABLE FREQUENCY
The minimum operating frequency that can be used for communications between two points.

LUMPED CONSTANTS
The properties of inductance, capacitance, and resistance in a transmission line.

LUMPED-IMPEDANCE TUNING
The insertion of an inductor or capacitor in series with an antenna to lengthen or shorten the antenna electrically. Also known as LOADING.

LOOSE COUPLING
Inefficient coupling of energy from one circuit to another that is desirable in some applications. Also called weak coupling.

MAJOR LOBE
The lobe in which the greatest amount of radiation occurs.

MARCONI ANTENNA
A quarter-wave antenna oriented perpendicular to the earth and operated with one end grounded. Also known as QUARTER-WAVE ANTENNA.

MAXIMUM USABLE FREQUENCY
Maximum frequency that can be used for communications between two locations for a given time of day and a given angle of incidence.

MEDIUM
The substance through which a wave travels from one point to the next. Air, water, wood, etc., are examples of a medium.

METALLIC INSULATOR
A shorted quarter-wave section of transmission line.

MINOR LOBE
The lobe in which the radiation intensity is less than a major lobe.

MULTI ELEMENT ARRAY
An array consisting of one or more arrays and classified as to directivity.

MULTI ELEMENT PARASITIC ARRAY
An array that contains two or more parasitic elements and a driven element.

MULTIPATH

NODE
The fixed minimum points of voltage or current on a standing wave or antenna.

NONDIRECTIONAL
See OMNIDIRECTIONAL,

NONRESONANT LINE
A transmission line that has no standing waves of current or voltage.

NULL
On a polar-coordinate graph, the area that represents minimum or 0 radiation.

OMNIDIRECTIONAL
Transmitting in all directions. Also known as NONDIRECTIONAL.

OPEN-ENDED LINE
A transmission line that has an infinitely large terminating impedance.

OPTIMUM WORKING FREQUENCY
The most practical operating frequency that can be used with the least amount of problems; roughly 85 percent of the maximum usable frequency.

OUTPUT IMPEDANCE
The impedance presented to the load by the transmission line and its source.

PARALLEL RESONANT CIRCUIT
A circuit that acts as a high impedance at resonance.

PARALLEL-WIRE
A type of transmission line consisting of two parallel wires.

PARASITIC ARRAY
An array that has one or more parasitic elements.

PARASITIC ELEMENT
The passive element of an antenna array that is connected to neither the transmission line nor the driven element.

PLANE OF POLARIZATION
The plane (vertical or horizontal) with respect to the earth in which the E-field propagates.

POWER GAIN
The ratio of the radiated power of an antenna compared to the output power of a standard antenna. A measure of antenna efficiency usually expressed in decibels. Also referred to as POWER RATIO.

POWER LOSS
The heat loss in current flows through it. a conductor as

POWER STANDING WAVE RATIO (PSWR)
The ratio of the square of the maximum and minimum voltages of a transmission line.

PROPAGATION
Waves travelling through a medium.

QUARTER-WAVE ANTENNA
See MARCONI ANTENNA.

The electromagnetic field that detaches itself from an antenna and travels through space.

The losses that occur when magnetic lines of force about a conductor are projected into space as radiation and are not returned to the conductor as the cycle alternates.

A plot of the radiated energy from an antenna.

The resistance, which if inserted in place of an antenna, would consume the same amount of power as that radiated by the antenna.

Electromagnetic frequencies that fall between 3 kilohertz and 300 gigahertz and are used for radio communications.

The boundary beyond the natural horizon in which radio waves cannot be propagated over the earth’s surface.

(1) A form of radiant energy that can neither be seen nor felt; (2) An electromagnetic wave generated by a transmitter.

RAREFIED WAVE
A longitudinal wave that has been expanded or rarefied (made less dense) as it moves away from the source.

The object that responds to a wave or disturbance. Same as detector.

RECEIVING ANTENNA
The device used to pick up an rf signal from space.

REFLECTED WAVE
(1) The wave that reflects back from a medium; (2) Waves travelling from the load back to the generator on a transmission line; (3) The wave moving back to the sending end of a transmission line after reflection has occurred.

REFLECTION WAVES
Waves that are neither transmitted nor absorbed, but are reflected from the surface of the medium they encounter.

REFLECTOR
The parasitic element of an array that causes maximum energy radiation in a direction toward the driven element.

REFRACTION
The changing of direction as a wave leaves one medium and enters another medium of a different density.

The reception and re-transmission of radio waves caused by turbulence in the troposphere.

RESONANCE
The condition produced when the frequency of vibrations are the same as the natural frequency (of a cavity), The vibrations reinforce each other.

RESONANT LINE
A transmission line that has standing waves of current and voltage.

RHOMBIC ANTENNA
A diamond-shaped antenna used widely for long-distance, high-frequency transmission and reception.

RIGID COAXIAL LINE
A coaxial line consisting of a central, insulated wire (inner conductor) mounted inside a tubular outer conductor.

SELF-INDUCTION
The phenomenon caused by the expanding and collapsing fields of an electron that encircles other electrons and retards the movement of the encircled electrons.

SERIES RESONANT CIRCUIT
A circuit that acts as a low impedance at resonance.

SHIELDED PAIR
A line consisting of parallel conductors separated from each other and surrounded by a solid dielectric.

SHORT-CIRCUITED LINE
A transmission line that has a terminating impedance equal to 0.

SKIN EFFECT
The tendency for alternating current to concentrate in the surface layer of a conductor. The effect increases with frequency and serves to increase the effective resistance of the conductor.

SKIP DISTANCE
The distance from a transmitter to the point where the sky wave is first returned to earth.

SKIP ZONE
A zone of silence between the point where the ground wave becomes too weak for reception and the point where the sky wave is first returned to earth.

SKY WAVES
Radio waves reflected back to earth from the ionosphere.

SOURCE
(1) The object that produces waves or disturbance; (2) The name given to the end of a two-wire transmission line that is connected to a source.

SPACE WAVE
A radio wave that travels directly from the transmitter to the receiver and remains in the troposphere.

SPECTRUM
(1) The entire range of electromagnetic waves; (2) VISIBLE. The range of electromagnetic waves that stimulate the sense of sight; (3) ELECTROMAGNETIC. The entire range of electromagnetic waves arranged in order of their frequencies.

Irregular cloud-like patches of unusually high ionization. Often forms at heights near the normal E-layer.

Insulator used with transmission lines and antennas to keep the parallel wires separated.

STANDING WAVE
The distribution of voltage and current formed by the incident and reflected waves, which have minimum and maximum points on a resultant wave that appears to stand still.

STANDING-WAVE RATIO (SWR)
The ratio of the maximum to the minimum amplitudes of corresponding components of a field, voltage, or current along a transmission line or waveguide in the direction of propagation measured at a given frequency. Measures the perfection of the termination of the line.

STRATOSPHERE
Located between the troposphere and the ionosphere. Has little effect on radio waves.

STUB
Short section of a transmission line used to match the impedance of a transmission line to an antenna. Can also be used to produce desired phase relationships between connected elements of an antenna.

SUDDEN IONOSPHERIC DISTURBANCE
An irregular ionospheric disturbance that can totally blank out hf radio communications.

SURFACE WAVE
A radio wave that travels along the contours of the earth, thereby being highly attenuated.

THREE-ELEMENT ARRAY
An array with two parasitic elements (reflector and director) and a driven element.

TRANSMISSION LINE
A device designed to guide electrical energy from one point to another.

TRANSMITTING ANTENNA
The device used to send the transmitted signal energy into space.

TRANSMISSION MEDIUMS
The various types of lines and waveguides used as transmission lines.

TROPOSPHERE
The portion of the atmosphere closest to the earth’s surface, where all weather phenomena take place.

TROPOSPHERIC SCATTER
The propagation of radio waves in the troposphere by means of scatter.

TROUGH (BOTTOM)
The peak of the negative alternation (maximum value below the line).

TUNED LINE
Another name for the resonant line. This line uses tuning devices to eliminate the reactance and to transfer maximum power from the source to the line.

TURNSTILE ANTENNA
A type of antenna used in VHF communications that is omnidirectional and consists of two horizontal half-wave antennas mounted at right angles to each other in the same horizontal plane.

TWISTED PAIR
A line consisting of two insulated wires twisted together to form a flexible line without the use of spacers.

TWO-WIRE OPEN LINE
A parallel line consisting of two wires that are generally spaced from 2 to 6 inches apart by insulating spacers.

A parallel line similar to a two-wire open line except that uniform spacing is assured by embedding the two wires in a low-loss dielectric.

UNIDIRECTIONAL ARRAY
An array that radiates in only one general direction.

UNTUNED LINE
Another name for the flat or nonresonant line.

V ANTENNA
A bidirectional antenna, shaped like a V, which is widely used for communications.

VELOCITY
The rate at which a disturbance travels through a medium.

VERTICAL PATTERN
The part of a radiation pattern that is radiated in the vertical plane.

VERTICAL PLANE
An imaginary plane that is perpendicular to the horizontal plane.

VERTICALLY POLARIZED
Waves radiated with the E-field component perpendicular to the earth’s surface.

VOLTAGE-FED
See END-FED.

VOLTAGE STANDING WAVE RATIO (VSWR)
The ratio of maximum to minimum voltage of a transmission line.

WAVE ANTENNA
See BEVERAGE ANTENNA.

WAVE MOTION
A recurring disturbance advancing through space with or without the use of a physical medium.

WAVE TRAIN
A continuous series of waves with the same amplitude and wavelength.

WAVEFRONT
A small section of an expanding sphere of electromagnetic radiation, perpendicular to the direction of travel of the energy.

WAVELENGTH
(1) The distance in space occupied by 1 cycle of a radio wave at any given instant; (2) The distance a disturbance travels during one period of vibration.

YAGI ANTENNA
A multi-element parasitic array. Elements lie in the same plane as those of the end-fire array.