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.
FREQUENCY DIVERSITY—Transmitting (and
receiving) of radio waves on two different
frequencies simultaneously.
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.
GENERATOR END—See INPUT END
GROUND PLANE—The portion of a groundplane
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.
H-FIELD—Any space or region in which a magnetic
force is exerted. The magnetic field may be
produced by a current-carrying coil or conductor,
by a permanent magnet, or by the earth itself.
Also known as MAGNETIC FIELD.
H-TYPE T-JUNCTION—A waveguide junction in
which the junction arm is parallel to the magnetic
lines of force in the main 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 frquency.
HERTZ ANTENNA—A half-wave antenna installed
some distance above ground and positioned either
vertically or horizontally.
HORN—A funnel-shaped section of waveguide used
as a termination device and as a radiating antenna.
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.
HYBRID JUNCTION—A waveguide junction that
combines two or more basic T-junctions.
HYBRID RING—A hybrid-waveguide junction that
combines a series of E-type T-junctions in a ring
configuration.
I2R LOSS—See COPPER LOSS.
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