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
INDUCTION FIELDThe electromagnetic field
produced about an antenna when current and
voltage are present on the same antenna.
INDUCTION LOSSESThe losses that occur when
the electromagnetic field around a conductor cuts
through a nearby metallic object and induces a
current into that object.
INPUT ENDThe end of a two-wire transmission
line that is connected to a source. Also known
as a GENERATOR END or a TRANSMITTER
INPUT IMPEDANCEThe impedance presented
to the transmitter by the transmission line and
INTERFERENCEAny disturbance that produces
an undesirable response or degrades a wave.
IONOSPHEREThe 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 STORMSDisturbances in the
earths magnetic field that make communications
practical only at lower frequencies.
IONIZATIONThe process of upsetting electrical
IRISA metal plate with an opening through which
electromagnetic waves may pass. Used as an
impedance matching device in waveguides.
ISOTROPIC RADIATIONThe radiation of energy
equally in all directions.
LEAKAGE CURRENTThe small amount of
current that flows between the conductors of a
transmission line through the dielectric.
LOAD ENDSee OUTPUT END.
LOAD ISOLATORA passive attenuator in which
the loss in one direction is much greater than that
in the opposite direction. An example is a ferrite
isolator for waveguides that allow energy to travel
in only one direction.
LOADINGSee LUMPED-IMPEDANCE TUNING.
LOBEAn area of a radiation pattern plotted on a
polar-coordinate graph that represents maximum
LONG-WIRE ANTENNAAn antenna that is a
wavelength or more long at its operating fre-
LONGITUDINAL WAVESWaves in which the
disturbance (back and forth motion) takes place
in the direction of propagation. Sometimes called
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 FREQUENCYThe minimum
operating frequency that can be used for commu-
nications between two points.
LUMPED CONSTANTSThe properties of
inductance, capacitance, and resistance in a
LUMPED-IMPEDANCE TUNINGThe inser-
tion of an inductor or capacitor in series with an
antenna to lengthen or shorten the antenna
electrically. Also known as LOADING.
LOOSE COUPLINGInefficient coupling of energy
from one circuit to another that is desirable in
some applications. Also called weak coupling.