RF Glossary: D | Terms Starting with D

dB (Decibel) — A logarithmic unit expressing the ratio of two power levels. 3 dB represents a doubling of power; 10 dB represents a tenfold increase.

dBc — Decibels relative to the carrier power level. Used to specify spurious signals, phase noise, and harmonics relative to the main signal.

dBi — Decibels of antenna gain relative to an isotropic radiator. The standard reference for expressing antenna gain.

dBm (Decibel-Milliwatt) — A unit of absolute power expressed in decibels relative to one milliwatt. 0 dBm equals 1 mW.

dBW — Decibels of power relative to one watt. Used in satellite and high-power link budgets. dBW = dBm - 30.

Demodulation — The process of extracting the original information signal from a modulated carrier wave.

Dielectric — An insulating material that supports an electric field with minimal energy dissipation. Characterized by its relative permittivity and loss tangent.

Dielectric Constant (Relative Permittivity) — The ratio of a material's permittivity to the permittivity of free space. Determines wave velocity and impedance in the material.

Diplexer — A three-port passive device that separates or combines two frequency bands while providing isolation between them.

Directivity — The ratio of an antenna's maximum radiation intensity to its average radiation intensity over all directions.

Dominant Mode — The propagation mode with the lowest cutoff frequency in a waveguide. For rectangular waveguide, this is the TE10 mode.

Down Converter — A frequency conversion device that translates an RF signal from a higher frequency to a lower intermediate frequency using a mixer and local oscillator.

Duplex — A communication mode allowing simultaneous transmission and reception, achieved through frequency division (FDD) or time division (TDD).

Dynamic Range — The range between the minimum detectable signal and the maximum signal a system can handle without distortion, typically expressed in dB.

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