Radar terms, and definitions

Decibel (dB): [dB] A dimension-less unit for expressing the ratio of two values of power, current, or voltage. The number of decibels being equal to: dB = 10 log P2/P1 = 20 log V2/V1 = 20 log I2/I1 Normally, used for expressing transmission gains, losses, levels, and similar quantities.

Deception: The deliberate radiation, re-radiation, alteration, absorption or reflection of electromagnetic energy in a manner intended to mislead the enemy interpretation or use of information received by his electronic systems.

dB: See Decibel

dBc: Decibels referenced to the carrier signal.

dBi: Decibels referenced to an isotropic radiator. (dBLi indicating linear isotropic radiator is sometimes used).

dBm: Decibels relative to 1 mW. dBm is calculated by using the ratio of some power (expressed in mW) to 1 mW. For example, 1 mW is 0 dBm and 10 mW is +10 dBm.

dBsm: Decibel referenced to one square meter.

dBv / dBFv: Decibels referenced to one volt or microvolt, i.e. 0 dBv is 1 volt or 120 dBuv.

dBW / dBuW: Decibels referenced to 1 watt or one microwatt, i.e. 0 dBW is 1 watt or 30 dBm or 60 dBuW.

Dead Space: The area, zone, or volume of space that is within the expected range of a radio, radar, or other transmitted signal but in which the signal is not detectable and therefore cannot be received.

Deflection: A change in the direction of a traveling particle, usually without loss of particle kinetic energy, representing a change in velocity without a change in the scalar speed of the particle. A change in the direction of a wave, beam, electron, or other entity, such as might be accomplished by an electric or magnetic field.

Deflection Coils: In a cathode-ray tube [CRT], coils used to bend an electron beam a desired amount.

Deionization Time: In a spark gap, the time required for ionized gas to return to its neutral state after the spark is removed.

Demodulator: A device employed to separate the modulation signal from its associated carrier, also called Second Detector. See also Detection.

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

Designation: The assignment of a fire control radar to a specific target by supplying target coordinate data to the radar system. Operational phase of a fire-control or track radar during which the radar is directed to the general direction of a desired target.

Detection: Usually refers to the technique of recovering the amplitude modulation signal (envelope) superimposed on a carrier.

Dielectrically Stabilized Oscillator: The DSO uses a dielectric resonator as the frequency determining element. When the dielectric material is properly selected and used, the variations in dielectric constant vs temperature and the dimensions of the resonant structure vs temperature tend to cancel out, providing relatively good frequency vs temperature stability. The DSO offers frequency accuracy and stability, low power consumption and high reliability. Some of the commonly used materials are barium, zirconium, or tin tinates. The composition of these materials may be controlled to achieve any frequency variation with temperature with close tolerances.

Dielectric Waveguide: A waveguide that consists of a dielectric material surrounded by another dielectric material, such as air, glass, or plastic, with a lower refractive index. Also refer to Manufacturers of Waveguides.