Communications, Radar & Electronic Warfare (201.. - Index of

Radio Links and Deliberate Jamming99Figure 6.5A barrage Jammer.Barrage januners require very high power, because the jamming energy is spreadover a wide bandwidth. Barrage januners can also be used to jam frequency hoppingsignals. In this case, it is not necessary to jam the entire frequencies used by thefrequency hopper. Similarly to the follower jammer, if at least one third of thefrequencies used by the hopper are jammed, then the jam will be effective.If more than one frequency needs to be jammed, an adaptive januner can be used.This uses the power available to the jammer to jam several signals simultaneously bysplitting the available power into the required number of channels. This is illustrated inFigure 6.6. Since the power available to the jammer is limited, the addition of each newchannel to be jammed reduces the power available for each channel. Thus, if twochannels are to be januned using the same power, the power in each channel is reducedby a factor of 2, and so on.If the technology of the enemy radio system is known, it may be possible to use 'smartjanuning' techniques. For example, for systems that use a control channel to manageaccess, the januner can be applied against this channel alone. This will prevent usersfrom achieving connectivity. Or, the januner can prevent packet acknowledgementsL-________ __________ IDetected enemy signalsD)Frequencya;:;:oQ.Adaptive jamming signalFrequencyFigure 6.6Illustration of an adaptive jammer. The available jamming power is split into the number ofchannels to be jammed, at the expense of the power available in each jammed channel.