DIRECTIONAL—Radiation that varies with direction.
DIRECTIONAL COUPLER—A device that samples the energy traveling in a waveguide for use in another circuit.
DIRECTOR—The parasitic element of an array that reinforces energy coming from the driver toward itself.
DIRECTIVITY—The property of an array that causes more radiation to take place in certain directions than in others.
DISTRIBUTED CONSTANTS—The constants of inductance, capacitance, and resistance in a transmission line. The constants are spread along the entire length of the line and cannot be distinguished separately.
DOMINANT MODE—The easiest mode to produce in a waveguide, and also, the most efficient mode in terms of energy transfer.
DOPPLER EFFECT—The apparent change in frequency or pitch when a sound source moves either toward or away from a listener.
DOUBLET—Another name for the dipole antenna.
DRIVEN ARRAY—An array in which all of the elements are driven. Also known as CONNECTED ARRAY
DRIVEN ELEMENT—An element of an antenna (transmitting or receiving) that is connected directly to the transmission line.
DUMMY LOAD—A device used at the end of a transmission line or waveguide to convert transmitted energy into heat so no energy is radiated outward or reflected back.
E-FIELD—Electric field that exists when a difference in electrical potential causes a stress in the dielectric between two points. Also known as ELECTRIC FIELD.
E-TYPE T-JUNCTION—A waveguide junction in which the junction arm extends from the main waveguide in the same direction as the E-field in the waveguide.
ECHO—The reflection of the original sound wave as it bounces off a distant surface.
ELECTROMAGNETIC FIELD—The combination of an electric (E) field and a magnetic (H) field.
ELECTROMAGNETIC INTERFERENCE—Man-made or natural interference that degrades the quality of reception of radio waves.
ELECTROMAGNETIC RADIATION—The radiation of radio waves into space.
ELECTRIC FIELD—See E-FIELD.
ELEMENT—A part of an antenna that can be either an active radiator or a parasitic radiator.
END-FEED METHOD—Connecting one end of an antenna through a capacitor to the final output stage of a transmitter. Also known as VOLTAGE-FEED METHOD.
END-FIRE ARRAY—An array in which the direction of radiation is parallel to the axis of the array.
ELEVATION ANGLE—The angle between the line of sight to an object and the horizontal plane.
FADING—Variations in signal strength by atmospheric conditions.
FEEDER—A transmission line that carries energy to the antenna.
FLAT LINE—A transmission line that has no standing waves. This line requires no special tuning device to transfer maximum power.
FLEXIBLE COAXIAL LINE— coaxial line made with a flexible inner conductor insulated from the outer conductor by a solid, continuous insulating material.
FOLDED DIPOLE—An ordinary half-wave antenna (dipole) that has one or more additional conductors connected across the ends parallel to each other.
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