Digital radio frequency memory
Encyclopedia
Digital Radio Frequency Memory (DRFM) is an electronic method for digital
ly capturing and retransmitting RF
signal. DRFMs are typically used in radar jamming, although applications in cellular
communications are becoming more common.
and bandwidth necessary to adequately represent the signal, then reconstruct that RF signal when required. The most significant aspect of DRFM is that as a digital "duplicate" of the received signal, it is coherent with the source of the received signal. As opposed to analog 'memory loops', there is no signal degradation caused by continuously cycling the energy through a front-end amplifier which allows for greater range errors for reactive jamming and allows for predictive jamming. A DRFM may modify the signal prior to retransmitting which can alter the signature of the false target; adjusting its apparent radar cross section
, range, velocity, and angle. DRFMs present a significant obstacle for radar sensors.
An example of the application of DRFM in jammers: The DRFM digitizes the received signal and stores a coherent copy in digital memory. As needed, the signal is replicated and retransmitted. Being a coherent representation of the original signal, the transmitting radar will not be able to distinguish it from other legitimate signals it receives and processes as targets. As the signal is stored in memory, it can be used to create false range targets both behind (reactive jamming) and ahead of (predictive jamming) the target intended for protection. Slight variations in frequency can be made to create Doppler (velocity) errors in the victim receiver as well. DRFM can also be used to create distorted phase-fronts at the victim receive antenna which is essential for countering monopulse radar angular measurement techniques.
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
ly capturing and retransmitting RF
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
signal. DRFMs are typically used in radar jamming, although applications in cellular
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
communications are becoming more common.
Overview
A DRFM system is designed to digitize an incoming RF input signal at a frequencyFrequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
and bandwidth necessary to adequately represent the signal, then reconstruct that RF signal when required. The most significant aspect of DRFM is that as a digital "duplicate" of the received signal, it is coherent with the source of the received signal. As opposed to analog 'memory loops', there is no signal degradation caused by continuously cycling the energy through a front-end amplifier which allows for greater range errors for reactive jamming and allows for predictive jamming. A DRFM may modify the signal prior to retransmitting which can alter the signature of the false target; adjusting its apparent radar cross section
Radar cross section
Radar cross section is a measure of how detectable an object is with a radar. A larger RCS indicates that an object is more easily detected.An object reflects a limited amount of radar energy...
, range, velocity, and angle. DRFMs present a significant obstacle for radar sensors.
An example of the application of DRFM in jammers: The DRFM digitizes the received signal and stores a coherent copy in digital memory. As needed, the signal is replicated and retransmitted. Being a coherent representation of the original signal, the transmitting radar will not be able to distinguish it from other legitimate signals it receives and processes as targets. As the signal is stored in memory, it can be used to create false range targets both behind (reactive jamming) and ahead of (predictive jamming) the target intended for protection. Slight variations in frequency can be made to create Doppler (velocity) errors in the victim receiver as well. DRFM can also be used to create distorted phase-fronts at the victim receive antenna which is essential for countering monopulse radar angular measurement techniques.