Radar terms, and definitions

GaAs FET AMPLIFIER: Because of their low noise, field-effect transistors are often used as the input stage of wideband amplifiers. Their high input resistance makes this device particularly useful in a variety of applications. Since the FET does not employ minority current carriers, carrier storage effects are eliminated giving the device faster operating characteristics and improved radiation resistant qualities. [GaAs IC Manufacturers]

GAIN: Any increase in the strength of a signal. For antennas, the value of power gain in a given direction relative to an isotropic point source radiating equally in all directions. Frequently expressed in dB (gain of an isotropic source = 0 dB).

GATE (RANGE): A signal used to select radar echoes corresponding to a very short range increment. Range is computed by moving the range gate or marker to the target echo; an arrangement which permits radar signals to be received in a small selected fraction of the time period between radar transmitter pulses.

GATED AGC: Circuit that permits automatic gain control to function only during short time intervals.

GATING: The process of selecting those portions of a wave which exist during one or more selected time intervals; The application of a square waveform of desired duration and timing to perform electronic switching; The application of receiver operating voltages to one or more stages only during that portion of a cycle of operation when reception is desired. See also Gate (Range).

GCI (GROUND-CONTROLLED INTERCEPT): vectoring an interceptor aircraft to an airborne target by means of information relayed from a ground-based radar site which observes both the interceptor and the target.

GIGA: A prefix meaning 10⁹ (times a billion). For example, gigahertz (GHz).

GLINT (In Radar): The random component of target location error caused by variations in the phase front of the target signal (as contrasted with Scintillation Error). Glint may affect angle, range of Doppler measurements, and may have peak values corresponding to locations beyond the true target extent in the measured coordinate. Electronic countermeasures that uses the scintillating, or flashing effect of shuttered or rotating reflectors to degrade tracking or seeking functions of an enemy weapons system.

GLOW DISCHARGE: Discharge of electricity through a gas in an electron tube.

GROUND CLUTTER: Unwanted echoes from surrounding land masses that appear on a radar indicator.

GROUND RANGE: The distance on the surface of the earth between a radar and its target. Equal to slant range only if both radar and target are at the same altitude.

GROUND-CONTROLLED APPROACH: Radar system used to guide aircraft to safe landings in poor visibility conditions.

GUARDBAND: A frequency band to which no other emitters are assigned as a precaution against interference to equipments susceptible to EMI in that band.

GUIDANCE, BEAM RIDER: A missile guidance technique which is dependent on the missile's ability to determine its positions with reference to the center of scan of the guidance radar beam and thus correct its trajectory on the basis of detected errors.

GUIDANCE CODE: A technique of modulating guidance transmitter carriers with coded pulses compatible with the receiver code of the missile assigned that system, thus reducing the possibility of the missile accepting erroneous commands of other transmissions.

GUIDANCE, COMMAND: A guidance system wherein intelligence transmitted to the missile from an outside source causes the missile to traverse a directed path in space.

GUIDANCE, HOMING, ACTIVE: A system of homing guidance wherein both the transmitter and receiver are carried within the missile.

GUIDANCE, HOMING, PASSIVE: A form of homing guidance, which is dependent on a missile's ability to detect energy emitted by the target. Frequently termed Home-On-Jam (HOJ).

GUIDANCE, HOMING, SEMIACTIVE: A system of homing guidance wherein the missile uses reflected signals from the target which has been illuminated by a source other than within the missile.

GUIDANCE, INERTIAL: A self-contained system independent of information obtained from outside the missile, usually using Newton's second law of motion.

GUNN DIODE: The Gunn diode is a transferred electron device which because of its negative resistance can be used in microwave oscillators or amplifiers. When the applied voltage exceeds a certain critical value, periodic fluctuations in current occur. The frequency of oscillation depends primarily upon the drift velocity of electrons through the effective length of the device. This frequency may be varied over a small range by means of mechanical tuning.