Radar terms, and definitions

CAPTURE BEAM: A wide beam incorporated in capture transmitters of beam rider (command guided) missile systems to facilitate gaining initial control of a missile immediately after launch. Upon capture, the system then centers the missile in the narrow guidance beam.

CAPTURE TRANSMITTER: A transmitter employing a wide beam antenna to gain initial control of in-flight missile for the purpose of centering the missile in the guidance transmitter antenna beam. See also Capture Beam.

CARRIER-CONTROLLED APPROACH. A shipboard radar system used to guide aircraft to safe landings in poor visibility conditions.

CARRIER FREQUENCY: The frequency of an unmodulated transmitter output. The basic radio frequency of the wave upon which modulations are impressed. Also called "Carrier" or Fc.

CARRIER POWER: (of a radio transmitter): The average power supplied to the antenna transmission line by a transmitter during one radio frequency cycle taken under the condition of no modulation. The average un-modulated power supplied to a transmission line.

CASSEGRAIN ANTENNA: An antenna in which the feed radiator is mounted at or near the surface of a concave main reflector and is aimed at a convex secondary reflector slightly inside the focus of the main reflector.
[Graphic of a Cassegrain Antenna below right]

CAVITY: A space enclosed by a conducting surface used as a resonant circuit at microwave frequencies. Cavity space geometry determines the resonant frequency. A storage area for oscillating electromagnetic energy.

C-BAND: A frequency band between 4 GHz and 6 GHz used in satellite communications. NOTE; "Letter designators of radio frequency bands are imprecise, deprecated, and legally obsolete."
Table of Frequency Bands

CENTER FREQUENCY: The tuned or operating frequency. Also referred to as center operating frequency. In frequency diversity systems, the midband frequency of the operating range. See also Carrier Frequency.

CHAFF Ribbon-like pieces of metallic materials or metallized plastic which are dispensed by aircraft or ships to mask or screen other "targets". The radar reflections off the chaff may cause a tracking radar to break lock on the target. The foil materials are generally cut into small pieces for which the size is dependent upon the radar interrogation frequency (approximately 1/2 wave length of the victim radar frequency). Being this length, chaff acts as a resonant dipole and reflects much of the energy back to the radar. Also see rainbow, rope, stream chaff, and window.

CHANNEL: A frequency or band of frequencies. In guided missile systems, an assigned center frequency and a fixed bandwidth around it. Designates operating frequency of track radars and frequency/code assignments of X-band CW illuminators.

CHIRP: A pulse compression technique which uses frequency modulation (usually linear) on pulse transmission.

CHIRP RADAR: See PC.

CIRCULARLY POLARIZED JAMMING: The techniques of radiating jamming energy in both planes of polarization simultaneously. With this method, there is a loss of 3 dB of effective power in either linear plane, and substantial loss if the opposite sense of circular polarization is used (i.e. left vs right).

CLUTTER: Confusing, unwanted echoes that interfere with the observation of desired signals on a radar indicator.

CLUTTER, RADAR: Undesired radar returns or echoes resulting from man-made or natural objects including chaff, sea, ground, and rain, which interfere with normal radar system observations. The figure illustrates a target being masked by ground clutter.

COAXIAL CABLE: A cable with one conductor completely surrounded by another conductor, separated by a dielectric.
Refer to the Definition of Coaxial Cable

CO-CHANNEL: The term is used to indicate that two (or more) equipments are operating on the same frequency.

COHERENT: A definite phase relationship between two energy waves, such as transmitted frequency and reference frequency. Two signals that have a set (usually fixed) phase relationship. COHERENT OSCILLATOR. In cw radar an oscillator that supplies phase references to provide coherent video from target returns.

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