Dictionary of Radar Terms
"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"

'Da' to 'Die', 'Dif' to 'Dn', 'Do' to 'Dz'

Difference Frequency: Beat Frequency; Difference and sum frequencies which result from combining two different frequencies.

Diffraction: The deviation of an electromagnetic wavefront from the path predicted by geometric optics when the wavefront interacts with, i.e., is restricted by, a physical object such as an opening (aperture) or an edge.

Diode: An electronic device which restricts current flow chiefly to one direction. Refer to definitions of Diode Types or, Diode Manufacturers.

Diode Types by Function Symbol
Diode Symbols

Diode Detector: A demodulator that uses one or more diodes to provide a rectified output with an average value that is proportional to the original modulation.

Diode Switch: PIN-diode switches provide state-of-the-art switching in most present-day microwave receivers. These switches are either reflective or non-reflective in that the former reflect incident power back to the source when in the isolated state. While both types of switches can provide high isolation and short transition times, the reflective switch offers multi octave bandwidth in the all shunt diode configuration, while the non-reflective switch offers an octave bandwidth. [Manufacturers of RF Switches]

Diplex: The simultaneous transmission or reception of two signals using a common feature such as a single antenna or carrier. Typically, two transmitters operate alternately at approximately the same RF and using a common antenna.

Directional Antenna: An antenna that radiates most effectively in only one direction. Antenna Terms

Directional Coupler: A transmission coupling device for separately sampling (through a known coupling loss) either the forward (incident) or the backward (reflected) wave in a transmission line. A 4-port transmission coupling device used to sample the power traveling in one direction through the main line of the device. There is considerable isolation (typically 20 dB) to signals traveling in the reverse direction. Because they are reciprocal, the directional coupler can also be used to directively combine signals with good reverse isolation. The directional coupler is implemented in waveguide and coaxial configurations.
Manufacturers of RF Directional Couplers

Directivity: Ability of an antenna to radiate or receive more energy in some directions than in others. The degree of sharpness of the antenna beam. For antennas, directivity is the maximum value of gain in a particular direction. (Isotropic point source has directivity = 1). For directional couplers, directivity is a measure (in dB) of how good the directional coupling is and is equal to the isolation minus the coupling.

Discriminator: A circuit in which amplitude variations are derived in response to phase or frequency variations.

Dish: A microwave reflector used as part of a radar antenna system. The surface is concave and is usually parabolic shaped. Also called a parabolic reflector.
Also refer to the listing covering vendors and Manufacturers of RF Dish.

The graphic shows a Military dish used by the US Army [TACSTAR].

US Military Satellite Dish Antenna
Dish Antenna
PC motherboard

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