Antenna terms, and definitions

Cable: An assembly of one or more insulated conductors, or optical fibers, or a combination of both, within an enveloping jacket. A cable is constructed so that the conductors or fibers may be used singly or in groups. Certain types of communications cables, especially long submarine cables but also terrestrial cables, whether the communications media are metallic or optical fiber, may contain metallic conductors that supply power to repeaters (amplifiers).

Cable assembly: A cable that is ready for installation in specific applications and usually terminated with connectors. [Cable assembly manufacturers]

Cable connectors: Fittings for cable ends which permit rapid connection and disconnection with equipment or other cables. [Cable connector manufacturers]

Capacitance: A natural property of an electrical circuit which opposes the rate of change of voltage. [Dictionary of Capacitor Terms]

Capacitor: A device for storing electrical charge. [Capacitor manufacturers]

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. Energy from the feed unit illuminates the secondary reflector, which reflects it back to the main reflector, which then forms the desired forward beam. The Cassegrain antenna design is adapted from optical telescope technology and allows the feed radiator to be more easily supported.

Cellular Communications: A cellular communications area is divided into smaller areas, called cells, and transmissions are passed from cell to cell until they reach their final destinations. Each cell must contain an antenna and transmission facilities to pick up signals from another cell or from a caller and to pass those signals on to an adjacent cell or to a caller within the cell. Cells can be anywhere from a few kilometers to 32 kilometers in diameter.

Center-fed: Transmission line connection at the electrical center of an antenna radiator.

Circuit noise level: At any point in a transmission system, the ratio of the circuit noise at that point to an arbitrary level chosen as a reference. Note: The circuit noise level is usually expressed in dBrn0, signifying the reading of a circuit noise meter, or in dBa0, signifying circuit noise meter reading adjusted to represent an interfering effect under specified conditions.

Circular polarization: In electromagnetic wave propagation, polarization such that the tip of the electric field vector describes a helix. The magnitude of the electric field vector is constant. The projection of the tip of the electric field vector upon any fixed plane intersecting, and normal to, the direction of propagation, describes a circle. A circularly polarized wave may be resolved into two linearly polarized waves in phase quadrature with their planes of polarization at right angles to each other. Circular polarization also referred to as "right-hand" or "left-hand," depending on whether the helix describes the thread of a right-hand or left-hand screw, respectively.

Coaxial cable: A transmission line consisting of two conductors, one inside the other, and separated by insulating material. The inner conductor may be a small copper tube or wire; the outer conductor may be metallic tubing or braid. Radiation loss from this type of line is very little. [Coax Cable Manufacturers]

Communications circuit: The means by which information is transferred between two or more places.

Conductor: A material (usually metal) that has low resistance to the flow of electrical current. A wire, cable, or other object capable of carrying electric current. Good conductors are made of metals such as silver, copper, and aluminum.

Connections: Points at which two or more conductors are brought into contact. Connector Manufacturers

CORNER-REFLECTOR ANTENNA. A half-wave antenna with a reflector consisting of two flat metal surfaces meeting at an angle behind the radiator.

Counterpoise: A conductor or system of conductors used as a substitute for ground in an antenna system; a wire or group of wires mounted close to the ground, but insulated from ground, to form a low-impedance, high-capacitance path to ground.

Critical frequency: The highest frequency at which a signal may be transmitted directly overhead and be reflected back to Earth from the ionosphere.

Cross-polarized: The polarization of a received signal is 90 degrees to the polarization of the receiving antenna.

Current: The flow of electrons along any path.

"D" Terms