Engineering Radar Definitions
"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"

Nautical Mile: The length of a minute of arc of a great circle of the earth (6,076 ft.)

Nautical Radar Mile: See Radar Mile.

Noise: In radar, erratic or random deflection or intensity of the indicator sweep that tends to mask small echo signals.

Noise Figure: The ratio of output noise to input noise in a receiver.

Noise Figure, Receiver: A figure of merit (NF or F) of a system given by the ratio of the signal-to-noise ratio at the input, Si / Ni, divided by the signal-to-noise ratio at the output, So / No . It essentially expresses the ratio of output noise power of a given receiver to that of a theoretically perfect receiver which adds no noise.Noise figure is usually expressed in dB and given for an impedance matched condition. Impedance mismatch will increase the noise figure by the amount of mismatch loss. NF is usually given at room temperature; 17EC or 290EK.

Noise Jamming: A continuous random signal radiated with the objective of concealing the aircraft echo from the enemy radar. In order for it to be effective, it must have an average amplitude at least as great as the average amplitude of the radar echo. There are three major categories of noise jamming which are grouped by how jamming power is concentrated: Spot, barrage, and swept jamming.

Noncoherent: Two signals that have no set phase relationship.

Notch: The portion of the radar velocity display where a target disappears due to being notched out by the zero Doppler filter. If not filtered (notched), ground clutter would also appear on the display. A notch filter is a narrow band-reject filter.

Null Antenna Pattern: The directions of minimum transmission (or reception) of a directional antenna. See also Lobe, Antenna. Antenna Dictionary

Null Fill: The nulls in an antenna pattern may be reduced (filled) by using a second ancillary (spoiler) antenna whose pattern is such that it fills in the nulls of the main antenna pattern.

Nutation: As applied to current missile system radars, this term refers to the mechanical motion of an antenna feed to produce a conical scan (fixed polarization) by the main beam of a tracking antenna, thus providing a means of developing tracking error signals. By analogy, "Nutation" also is used to denote the electrical switching of the quadrants of a seeker antenna. The effect is similar to that of a conical scan.

Nutator: A motor-driven rotating antenna feed used to produce a conical scan for a tracking radar. See also Antenna, Nutating. Also, the electrical circuits necessary to effect non-mechanical conical scans.

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