REFLECTOR—The parasitic element of an array
that causes maximum energy radiation in a
direction toward the driven element.
REFRACTION—The changing of direction as a wave
leaves one medium and enters another medium
of a different density.
REFRACTIVE INDEX—The ratio of the phase
velocity of a wave in free space to the phase
velocity of the wave in a given substance
(dielectric).
RERADIATION—The reception and retransmission
of radio waves caused by turbulence in the
troposphere.
RESONANCE—The condition produced when the
frequency of vibrations are the same as the natural
frequency (of a cavity), The vibrations reinforce
each other.
RESONANT LINE—A transmission line that has
standing waves of current and voltage.
RHOMBIC ANTENNA—A diamond-shaped antenna
used widely for long-distance, high-frequency
transmission and reception.
RIGID COAXIAL LINE—A coxial line consist-
ing of a central, insulated wire (inner conductor)
mounted inside a tubular outer conductor.
ROTATING JOINT—A joint that permits one sec-
tion of a transmission line or waveguide to rotate
continuously with respect to another while passing
energy through the joint. Also called a rotary
coupler.
SCATTER ANGLE—The angle at which the
receiving antenna must be aimed to capture the
scattered energy of tropospheric scatter.
SELF-INDUCTION—The phenomenon caused by
the expanding and collapsing fields of an electron
that encircles other electrons and retards the
movement of the encircled electrons.
SERIES RESONANT CIRCUIT—A circuit that
acts as a low impedance at resonance.
SHIELDED PAIR—A line consisting of parallel
conductors separated from each other and
surrounded by a solid dielectric.
SHORT-CIRCUITED LINE—A transmission line
that has a terminating impedance equal to 0.
SKIN EFFECT—The tendency for alternating current
to concentrate in the surface layer of a conductor.
The effect increases with frequency and serves
to increase the effective resistance of the conduc-
tor.
SKIP DISTANCE—The distance from a transmitter
to the point where the sky wave is first returned
to earth.
SKIP ZONE—A zone of silence between the point
where the ground wave becomes too weak for
reception and the point where the sky wave is
first returned to earth.
SKY WAVES—Radio waves reflected back to earth
from the ionosphere.
SLOT—Narrow opening in a waveguide wall used
to couple energy in or out of the waveguide. Also
called an APERTURE or a WINDOW.
SOURCE—(1) The object that produces waves or
disturbance; (2) The name given to the end of
a two-wire transmission line that is connected
to a source.
SPACE DIVERSITY—Reception of radio waves by
two or more antennas spaced some distance apart,
SPACE WAVE—A radio wave that travels directly
from the transmitter to the receiver and remains
in the troposphere.
SPECTRUM—(1) The entire range of electromagnetic
waves; (2) VISIBLE. The range of electromag-
netic waves that stimulate the sense of sight;
AI-8
