Radar terms, and definitions

I Band. A range of frequencies between 8 and 10GHz.

I Band Radar

IF: [Intermediate Frequency] The difference frequency resulting from mixing (beating) the received signal in a super-heterodyne receiver with the signal from the local oscillator. The difference frequency product provides the advantages inherent to the processing (amplification, detection, filtering, and such) of low frequency signals. The receiver local oscillator may operate either below or above the receiver tuned frequency. A single receiver may incorporate multiple IF detection. IF = FLO - FO . (for a local oscillator operating above the fundamental) where: FO = Received fundamental frequency FLO = Local oscillator frequency. See also Image Frequency.

IF Amplifier: Usually a narrow-bandwidth IF amplifier that is tuned to one of the output frequencies produced by the mixer.

IFF: [Identification Friend of Foe] A system using radar transmission to which equipment carried by friendly forces automatically responds by emitting a unique characteristic series of pulses thereby distinguishing themselves from enemy forces. It is the "Mode IV" for the aircraft transponder.

Image Frequency: That frequency to which a given super heterodyne receiver is inherently susceptible, thereby rendering such a receiver extremely vulnerable to EMI at that frequency. The image frequency is located at the same frequency difference to one side of the local oscillator as the tuned (desired) frequency is to the other side. An undesired signal received at the image frequency by a superheterodyne receiver not having pre-selection would, therefore, mix (beat) with the oscillator, produce the proper receiver IF, and be processed in the same manner as a signal at the desired frequency. See also receiver selectivity.

Image Jamming: Jamming at the image frequency of the radar receiver. Barrage jamming is made most effective by generating energy at both the normal operating and image frequency of the radar. Image jamming inverts the phase of the response and is thereby useful as an angle deception technique.

IMPATT Diode: The IMPATT (IMPact Avalanche and Transit Time) diode acts like a negative resistance at microwave frequencies. Because of this property, Impatt diodes are used in oscillators and amplifiers. Usually the frequency range is in the millimeter wave region where other solid state devices cannot compete. Also refer to the general engineering dictionary entry for Diode Terms. In addition, see Manufacturers of Diodes, for a list of companies producing them.

Index of Refraction: The degree of bending of an RF wave when passing from one medium to another.

Indicator: Equipment that provides a visual presentation of target position information. Also refer to an R-Scope display. The graphic shows a radar display used as a target indicator in a B52 bomber.

Ingress: Go into the target area.

Insertion Loss: The loss incurred by inserting an element, device, or apparatus in an electrical/electronic circuit. Normally expressed in decibels determined as 10 log of the ratio of power measured at the point of insertion prior to inserting the device (P1) to the power measured after inserting the device (P2). Insertion loss (dB) = 10 log P1/P2.

Integration Effect: Pulse radars usually obtain several echoes from a target. If these echoes are added to each other, they enhance the S/N ratio, making a weak target easier to detect. The noise and interference do not directly add from pulse to pulse, so the ratio of target strength to undesired signal strength improves making the target more detectable. Random noise increases by the square root of the number of integrations, whereas the signal totally correlates and increases directly by the number of integrations, therefore the S/N enhancement is equal to the square root of the number of integrations.