Electronic Protection. Methods

Electronic protection, also known as electronic-counter-counter measures, concerns techniques and technologies intended to preserve the ability of defense electronic systems to operate in hostile electromagnetic environments.

Active EP includes measures taken to enhance the ability of defense electronic equipment to operate without hindrance by enemy EW.

Protection against intercept and jamming of communication signals can be provided in various ways:
1 .Equipment can be designed to operate over wide frequency ranges, which offers improved opportunities for a system to switch to quieter frequencies if interference or jamming is encountered;

2. Directional antennas can be employed to make the interception of a signal difficult for a receiver outside the main beam response of the transmitting antenna. Jamming resistance can be achieved if the direction that the jamming signal is coming from corresponds to a null in the receiving antenna directional response.

3. Careful choices of sites may be able to take advantage of terrain masking of areas potentially usable by jammers or ES systems;
4. Power management allows the transmitter power to be set at the minimum level required for reliable communication. Low-power operation is desirable for short-range communication because the range at which the signal can be detected and intercepted is reduced. High power levels can be used to provide reliable operation over longer ranges and/or to overcome jamming;

5. Low probability of intercept techniques can be used to render DF and intercept difficult. FH techniques are widely used by modern tactical radios;

6. Redundancy can be achieved by design and/or tactical procedures to limit the damage caused by the effects of enemy EA; for example, different types of communication systems can be networked and managed to ensure that the disruption of one system does not prevent the communication of important information.

Similar techniques are applicable to radar systems with several differences:
1. A radar system may be able to search over a restricted range of angles and still perform its mission requirements. An ES system outside the search area will not be illuminated by the mainbeam of the radar antenna and may have difficulty detecting the signals;

2. Radar antennas are generally designed to be highly directive to provide angle resolution. However, antenna designs that also achieve low sidelobe levels are desirable for several reasons. First, sensitive ES systems can usefully detect pulses that correspond to the antenna sidelobes if these are sufficiently large. Second, some jamming techniques make use of signals that are received through sidelobes in the radar antenna response and therefore confuse the radar into showing a target at an angle offset from the jammer;

3. Frequency agility involves changing the transmitter frequency pulse to pulse or between groups of pulses. It has some similarities to the use of FH by communication systems, although the primary ideas are to complicate the task of an ES system in interpreting whether the received pulses are from one or more radars, and to reduce the effectiveness of single frequency jammers.

4. LPI radars tend to use continuous wave signals with frequency or phase modulation to provide the desired range resolution. Technical considerations generally restrict the average transmitter power with the result that they are most suited to applications in which long range is not required.

Against these signals, conventional radar ES systems are usually limited to very short detection ranges because of the low transmitter power and the effect of receiver optimizations for the processing of short duration pulse signals.

Passive EP generally places considerable emphasis on training and operational procedures. Some of the most spectacular EW successes, such as the decryption of messages ciphered by the German Enigma machine in WW2, resulted, at least in part, from the failure of radio operators to follow correct procedures.

The security of communication systems can be compromised in many possible ways. Examples include the transmission of unimportant or unnecessarily long messages; the repeated transmission of the same message with and without encryption; the failure to use code words and available EP capabilities, such as power management, FH, and encryption; and the failure to safeguard encryption equipment and keys. The likelihood of such lapses can be reduced substantially by the institution of suitable procedures followed by training under realistic conditions.

Emission Security policy includes defining procedures and techniques for minimizing the possibility of sensitive information being obtained from the intercept of RF signals that are generated unintentionally in the operation of computer or other electronic systems.

In field or operational environments, tactical EP strategy is set by Emission Control (EMCON) orders, which define specific rules for the management of electromagnetic emissions (12) during a military operation. These rules attempt to strike a balance between various requirements:

1. Maintaining command and control capabilities;
2. Limiting mutual interference between friendly systems;
3. Limiting the useful information that enemy ES can provide;
4. The execution of deception operations.

EMCON rules include the following:
1. Restrictions on transmit power times and use of radio black-out policy;
2. Guidelines, such as frequency allocations and approved system configurations;
3. Restrictions on the type of information that can be transmitted (and thus denied to the enemy).