Radar terms, and definitions

Aperture: In an antenna, that portion of the plane surface area near the antenna perpendicular to the direction of maximum radiation through which the major portion of the radiation passes. The effective and/or scattering aperture area can be computed for wire antennas which have no obvious physical area.

Apogee: The point in the orbit of a satellite when it's the greatest distance from the earth.

A-Scope: A cathode-ray oscilloscope used in radar systems to display vertically the signal amplitude as a function of time (range) or range rate. Sometimes referred to as Range (R)-Scope. See R-Scope for an A-Scope Display graphic. A radar display on which slant range is shown as the distance along a horizontal trace.

Aspect Angle: The angle of an object relative to a reference.

Asynchronous Orbit: One where the satellite does not rotate or move at the same speed as the earth.

Asynchronous Pulsed Jamming: The form of jamming that nearly matches the pulse repetition frequency (PRF) of the radar, but also transmits multiples of the PRF. Asynchronous pulsed jamming is similar to synchronous jamming except that the target lines tend to curve inward or outward slightly and appear fuzzy in the jammed sector of a radar scope.

Attenuation: Decrease in magnitude of current, voltage, or power of a signal in transmission between two points. May be expressed in decibels. [RF Attenuator Manufacturers]. Refer to MIL-DTL-3933 Attenuators, Fixed General Specification for (M3933/14-). [general requirements for radio and microwave frequency fixed attenuators, including chip, coaxial, leaded, and relay header attenuators].

SMA Attenuator

Automatic Frequency Control: [AFC] An arrangement whereby the frequency of an oscillator or the tuning of a circuit is automatically maintained within specified limits with respect to a reference frequency. A magnetron drifts in frequency over a period of time. The AFC of a radar makes the local oscillator shift by an equal amount so the IF frequency will remain constant.

Automatic Gain Control: [AGC] A method for automatically obtaining an essentially constant receiver output amplitude. The amplitude of the received signal in the range gate determines the AGC bias (a DC voltage) which controls the receiver gain so as to maintain a nearly constant output even though the amplitude of the input signal changes.

Average Power: Output power of a transmitter as measured from the start of one pulse to the start of the next pulse.

Azimuth: Angular measurement in the horizontal plane in a clockwise direction.