ECCM, the modern war
ECCM always subjected to discussions taken in remote rooms far from scrutinizing eyes and out of public ears. ECCM or in most common name Electronic Counter Counter-Measurements is a technique use for deteriorating jammers and reduce the enemy's effective usage of electromagnetic spectrum or any other EM method used by ECM (Electronic Counter Measurements) equipment - ECCM is about defending against ECM techniques and rendering them ineffective.
The Electronic warfare is old almost as the early days of the communication era. The first reported conflict involving the usage of EW was the Russia-Japanese War of 1905, when Russian naval commanders attempted to jamm radio transmissions from Japanese ships to headquarter. As the communication transmission becomes more vital to the combat for maintaining connection for synchronization between divisions and maneuver forces, advanced attempts to tether electronics measurements to cope with the enemy transmissions that were executed. ECCM can be traced back to World War II when the British disrupted German radio communications using jamming techniques. To counter the British jammer, the German military increased the transmission power of their radio signals to overpower the jamming.
The word radar was a code name used by the US Navy in 1940, and is an acronym derived from the phrase RAdio Detection And Ranging. During World War II, the use of radar became widespread due to the increase of the Germans air raids. The Radar enabled the British the opportunity to focus the Royal Air Force resources into specific air space and to intercept the German Luftwaffe air force offense. The operational concept of active Radar was not changed dramatically from the beginning of the second World War (passive Radars and EOP solutions are no part of this article and might be part of future article). Radio waves are radiated from the radar into the free space. Some of the radio waves will progress and vanish in the space. However, some of the waves may hit an object and will be reflected (echo) and directed toward the radar. The intensity of the echo depends on the size and the shape of the object and its name is Radar Cross Section(RCS) . Radar Cross Section is the term used to describe the combination of shape, size and reflection material and it is expressed in square meters. Targets with higher RCS reflects more radio waves and causes a stronger echo signal that can be detected by the radar. The main ballpark of the ECM operation is in the echo signal and its main target is to use a technique to reduce the real echo signal value from a fake signal that the ECM equipment stored onboard of the target. The main advantage of the radar is the ability to track objects appears in the operational environment and to aim kinetics solution used to neutralize objects before the objects exceeds soft possession elements in the area needs to be defended. There are several techniques to track objects and the number of these techniques always keeps rise with technology evolutionary. The Electronic Counter Measurements keeps the pace with the radar advance and introduces resilient jammers/deception techniques as described in the Research and Development Technical Report of the US Army Communication Command Fort Monmouth, New Jersey:
The signal-to-jamming ratio is a relative strength between the desired signal (echo) to the jamming signal at the receiver. Signal refers to the echo receive from the flying object. Jamming refers to the hostile or unidentified interference being received. It is always best to have a signal-to-jamming ratio in which the desired signal is stronger than the jamming signal. There is a slight advantage to the jammer on the signal hence the jammers signal moves only one direction (from the airplane to the radar) unlike the radar signal that moves both ways. On the other hand, the radar has almost no limitation of power radiating.
? Side lobe canceller (SLC) – The side lobes are Achilles' heel of each radar system. Side lobes enables the jammer to hit the radar even when the radar does not aim the main lobe toward the jammer. Therefore, a strong jammer/ deception can impact the radar 360 in azimuth. For implementing SLC the system uses several auxiliary antennas that captures signals may appear in the side lobe. Estimation from the auxiliary antennas results in suppression of the interference.
? NULL-Steering - In null steering algorithms, the weights of an antenna array are selected such that the directional pattern has nulls in particular directions. In this manner, undesirable interference, jamming signals, or noise can be reduced or eliminated. Using several energy sources impacts the total wave propagation as introduced by Thomas Young in his famous experiment that demonstrated the constructive and destructive interference of light. The superposition principle determines the resulting intensity pattern. When controlling the phase propagation, we can control the NULL pointing direction and cancel strong jammers signal at a certain azimuth.
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? Frequency agility (Frequency hopping) – The need to produce extensive energy to jamm large bandwidth focused the jammers to implement fast monitors for sampling the spectrum and to lock the specific frequency transmitted by the radar and to have high power jamming in the specific spectral frequency. The frequency agility refers to the radar's ability to quickly change its frequency within its operating band. Pulse-to-pulse frequency shift or changing the transmitter frequency radically during every interpulse is one of the ultimate in frequency agility.
? Doppler filtering - This ECCM technique is for use on a tracking doppler radar to detect doppler targets and to aid in defeating velocity deception techniques. An MTI (moving target indicator) pulsed radar system uses a number of gates and corresponding narrow bandpass filters to discriminate moving targets from a background of clutter or slowly moving chaff particles. In essence, Doppler filtering is a radar ECCM and anti-clutter technique.
? Phase compare – Some of the ECM techniques uses non-coherent pulses therefore a decent radar can compare the received pulse phase and can identify spoofed pulses tailored in an ECM mechanism.
? Spread Spectrum refers to a system originally developed for military applications, to provide secure communications by spreading the signal over a large frequency band. The signal spreading eliminates the ECM receiver to identify spread signals and to build its technique because a spread signal is in the amplitude range of the nature noise. However, when the ECM transmits a simple jamming signal (according to pre-defined information) it can easily jamm the spread spectrum receiver. A combination of spread spectrum receiver with frequency agility produces robust ECCM system.
? Pulse stamping – The radar's transmission channel stamps each transmitted pulses with a different identification. This mechanism implements authentication procedure for each pulse that is received in the receive channel. The mechanism verifies that each pulse is an authentic pulse and was not created by synthetic ECM mechanism. This method eliminates fake decoy signals created by stand off ECM system.
? Advance analytics – The most common mechanism used by an ECM system is to create a synthetic pulse similar to the origin pulse of the radar and to create some tweaks (not part of this article) to convince the radar on specific maneuvers that causes the radar to prefer the synthetic pulse instead of the origin radar pulse . The main target of the tweaks pulses is to cause the radar to aim its main beam for different location that is far enough from the airplane. The radar analytics uses Kalman filter to verify the correctness of the received pulse in amplitude and continuous and correct flight position.
The most advanced ECCM systems involves in defending from cyber-attacks that aims themselves to hit a prey in a similar manner of conventional code injection attacks of injecting malicious code into a vulnerable computer or network to change its course of action.