DIRECTIONAL.Radiation that varies with direction.
DIRECTIONAL COUPLERA device that samples
the energy traveling in a waveguide for use in
DIRECTORThe parasitic element of an array that
reinforces energy coming from the driver toward
DIRECTIVITYThe property of an array that causes
more radiation to take place in certain directions
than in others.
DISTRIBUTED CONSTANTSThe constants of
inductance, capacitance, and resistance in a
transmission line. The constants are spread along
the entire length of the line and cannot be
DOMINANT MODEThe easiest mode to produce
in a waveguide, and also, the most efficient mode
in terms of energy transfer.
DOPPLER EFFECTThe apparent change in
frequency or pitch when a sound source moves
either toward or away from a listener.
DOUBLETAnother name for the dipole antenna.
DRIVEN ARRAYAn array in which all of the
elements are driven.
Also known as CON-
DRIVEN ELEMENTAn element of an antenna
(transmitting or receiving) that is connected
directly to the transmission line.
DUMMY LOADA 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-FIELDElectric field that exists when a difference
in electrical potential causes a stress in the
dielectric between two points. AlSO known as
E-TYPE T-JUNCTIONA waveguide junction in
which the junction arm extends from the main
waveguide in the same direction as the E-field
in the waveguide.
ECHOThe reflection of the original sound wave
as it bounces off a distant surface.
ELECTROMAGNETIC FIELDThe combination
of an electric (E) field and a magnetic (H) field.
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 FIELDSee E-FIELD.
ELEMENTA part of an antenna that can be either
an active radiator or a parasitic radiator.
END-FEED METHODConnecting one end of an
antenna through a capacitor to the final output
stage of a transmitter.
Also known as
END-FIRE ARRAYAn array in which the direction
of radiation is parallel to the axis of the array.
ELEVATION ANGLEThe angle between the line
of sight to an object and the horizontal plane.
FADINGVariations in signal strength by atmo-
FEEDERA transmission line that carries energy
to the antenna.
FLAT LINEA 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
FOLDED DIPOLEAn ordinary half-wave antenna
(dipole) that has one or more additional conduc-
tors connected across the ends parallel to each