DIRECTIONAL.—Radiation that varies with direction.
DIRECTIONAL COUPLER—A device that samples
the energy traveling in a waveguide for use in
another circuit.
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.
DOMINANT MODE—The easiest mode to produce
in a waveguide, and also, the most efficient mode
in terms of energy transfer.
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.
Also known as CON-
NECTED ARRAY
DRIVEN ELEMENT—An element of an antenna
(transmitting or receiving) that is connected
directly to the transmission line.
DUMMY LOAD—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.
E-FIELD—Electric field that exists when a difference
in electrical potential causes a stress in the
dielectric between two points. AlSO known as
ELECTRIC FIELD.
E-TYPE T-JUNCTION—A waveguide junction in
which the junction arm extends from the main
waveguide in the same direction as the E-field
in the waveguide.
ECHO—The reflection of the original sound wave
as it bounces off a distant surface.
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.
E L E C T R O M A G N E T I C R A D I A T I O N — T h e
radiation of radio waves into space.
ELECTRIC FIELD—See E-FIELD.
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.
Also known as
VOLTAGE-FEED METHOD.
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.
FADING—Variations in signal strength by atmo-
spheric 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 conduc-
tors connected across the ends parallel to each
other.
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