APPENDIX I
GLOSSARY
A
ANTENNA— A device used to radiate or receive radio
waves.
ANTENNA COUPLER— A device used for impedance
matching (tuning) between an antenna and a transmitter
or receiver.
ANTENNA RECIPROCITY— The ability of an antenna
to both transmit and receive electromagnetic energy.
ANTENNA TUNING— The process where an antenna is
electrically “matched” to the output frequency and
impedance of the transmitter.
ATTENUATION— A deliberate reduction or an
unintended loss in RF signal strength.
B
BANDWIDTH— Any section of the frequency spectrum
occupied by specific signals.
BIDIRECTIONAL ANTENNA— An antenna that
radiates in or receives most of its energy from only two
directions.
BLACK— Cipher text or encrypted text or information
C
CARRIER— The unmodulated signal originally produced
in the oscillator section of a transmitter.
CARRIER FREQUENCY— The final RF output without
modulation. The assigned transmitter frequency.
CHANNEL— A carrier frequency assignment, usually with
a fixed bandwidth.
COMPLEX WAVE— A transmitted radio signal
composed of different frequencies.
COUNTERPOISE— The ground plane, or reflective
surface, comprising an antenna’s reflected image at a
given wavelength.
CRITICAL FREQUENCY— The highest transmitted
frequency that can be propagated directly upward and
still be bent, or “refracted,” back to Earth.
CYCLE— Two complete alternations of alternating current,
or one complete revolution in any period of time, equal
to 360°.
D
DAMA (DEMAND ASSIGNED MULTIPLE ACCESS
SUBSYSTEM)— Subsystem that multiplexes several
subsystems on one satellite channel.
DIFFRACTION— The bending of radio waves around the
edges of a solid objector dense mass.
DIRECTIONAL ANTENNA— An antenna that radiates
or receives radio waves more effectively in some
directions than in others.
DIRECTIVITY— The sharpness or narrowness of an
antenna’s radiation pattern in a given plan.
DIRECT WAVE— A radio signal that travels in a direct
line-of-sight path from the transmitting antenna to the
receiving antenna.
DUMMY LOAD— A nonradiating device used at the end
of a transmission line in place of an antenna for tuning a
transmitter, The dummy load converts transmitted
energy into heat so that no energy is radiated outward or
reflected back.
E
EHF (EXTREMELY HIGH FREQUENCY)— The band
of frequencies from 30 GHz to 300 GHz.
ELECTRIC FIELD— A field produced as a result of a
voltage charge on an antenna.
ELECTROMAGNETIC ENERGY— An RF source
composed of both an electric and a magnetic field.
ELECTROMAGNETIC WAVES— Energy produced at
the output of a transmitter; also called radio waves.
F
FADING— Variation, usually gradual, in the field strength
of a radio signal that is caused by changes in the
transmission path or medium.
AI-1
