AI-3
DIFFUSION—The scattering of reflected light waves (beams) from an object, such as white paper.
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—Radiation that varies with direction.
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.
DISPERSION—The refraction of light waves that causes the different frequencies to bend at slightly
different angles.
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.
DOPPLER EFFECT—The apparent change in frequency or pitch when a sound source moves either
toward or away from a listener.
DOUBLET—Another name for the dipole antenna.
DRIVEN ARRAY—An array in which all of the elements are driven.
DRIVEN ELEMENT—An element of an antenna (transmitting or receiving) that is connected directly
to the transmission line.
ECHO—The reflection of the original sound wave as it bounces off a distant surface.
ELASTICITY—The ability of a substance to return to its original state.
ELECTROMAGNETIC FIELD—The combination of an electric (E) field and a magnetic (H) field.
ELECTROMAGNETIC INTERFERENCE—Man-made or natural interference that degrades the
quality of reception of radio waves.
ELECTROMAGNETIC RADIATION—The radiation of radio waves into space.
ELECTRIC (E) FIELD—The field produced as a result of a voltage charge on a conductor or antenna.
ELEMENT—A part of an antenna that can be either an active radiator or a parasitic radiator.
END-FEED METHOD—Connecting one end of an antenna through a capacitor to the final output stage
of a transmitter.
END-FIRE ARRAY—An array in which the direction of radiation is parallel to the axis of the array.
FADING—Variations in signal strength by atmospheric conditions.
FEEDER—A transmission line that carries energy to the antenna.
