AI-4
FLAT LINE—A transmission line that has no standing waves. This line requires no special tuning
device to transfer maximum power.
FLEXIBLE COAXIAL LINE—A 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 conductors
connected across the ends parallel to each other.
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.
HALF-WAVE DIPOLE ANTENNA—An antenna consisting of two rods (1/4 wavelength each) in a
straight line, that radiates electromagnetic energy.
HARMONIC—A frequency that is a whole number multiple of a smaller base frequency.
HERTZ ANTENNA—A half-wave antenna installed some distance above ground and positioned either
vertically or horizontally.
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.
