Antenna terms for Engineers and Technicians
"A", "B", "C", "D", "E", "F", "G"/"H", "I"/"J"/"K"/"L", "M"/"N"/"O",
"P"/"Q", "R", "S", "T", "U"/"V"/"W"/"X"/"Y"/"Z"

D to Dir, Dis to Dz,

dBa: Abbreviation for decibels adjusted. Weighted absolute noise power, calculated in dB referenced to 3.16 picowatts (-85 dBm), which is 0 dBa. A one-milliwatt, 1000-Hz tone will read +85 dBa, but the same power as white noise, randomly distributed over a 3-kHz band (nominally 300 to 3300 Hz), will read +82 dBa, due to the frequency weighting. Synonym dBrn adjusted.

dBc: Abbreviation. dB relative to the carrier power.

dBi: Abbreviation. dB referenced to the gain of an isotropic antenna [omnidirectional] with 100 percent efficiency.

Decibel: The standard unit used to express transmission gain or loss and relative power levels. Also called dB.

Deflection: The displacement of an electron beam from its line of sight path.

Demodulate: To recover the information originally impressed on the radio wave.

Departure Angle: The angle between the axis of the main lobe of an antenna pattern and the horizontal plane at the transmitting antenna.

Despun Antenna: An antenna on a communications satellite with a main beam that is continuously redirected with respect to the satellite so that the antenna illuminates a given area on the surface of the Earth, i.e., the footprint does not move with respect to the Earth.

DF Antenna. Direction Finding Antenna.

Dielectric: A material that does not conduct electricity, such as rubber or glass, i.e. an insulator.

Dielectric Antenna: -- Text in Review.

Dielectric Rod Antenna: -- Text in Review.

Diffraction: The process by which electromagnetic waves are bent so that they appear behind an obstruction.

Diplex Operation: The sharing of one common element, such as a single antenna or channel, for transmission or reception of two simultaneous, independent signals on two different frequencies.

Dipole antenna: A center-fed wire antenna whose conductors are in a straight line. Usually a straight, center-fed, one-half wavelength antenna.

Dipole Antenna
Dipole Antenna

Directional Antenna: An antenna designed to transmit and receive RF energy in a specific direction(s). An antenna that radiates most effectively in only one direction. An antenna that radiates most effectively in some directions directions than in others. An antenna in which the radiation pattern is not omnidirectional.

Directive Gain: Of an antenna, the ratio of (a) 4% times the radiance, i.e., power radiated per unit solid angle (watts per steradian), in a given direction to (b) the total power, i.e., the power radiated to 4% steradians.

Direct waves: Waves which propagate in a straight line from the transmitting to the receiving antennas, which only occurs when the antenna are Line-of-Sight [LOS]. The distance direct waves travel may be increased by increasing the height of the antennas. Direct wave propagation does not use or depend on sky waves.

Directive Gain. Of an antenna, the ratio of (a) 4% times the radiance, i.e., power radiated per unit solid angle (watts per steradian), in a given direction to (b) the total power, i.e., the power radiated to 4% steradians.

Directivity: The property of radiating more energy in some directions than in others.

Director: A conductor placed in front of a driven element to cause directivity.

 
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