RADAR Countermeasures

Electronic Warfare (EW)

Three branches

1. Electronic Support Measures (ESM) → Electronic Support (ES)

2. Electronic Counter Measures (ECM) → Electronic Attack (EA)

3. Electronic Counter-Counter Measures (ECCM) → Electronic Protection (EP

Electronic Support Measures

• Search the radio spectrum for emissions and analyse the results, identifying friendly, neutral, and enemy electronic emissions

• Provides warning of potential attack, knowledge of enemy capabilities and an indication of enemy use of active countermeasures.

Requirements of an ESM receiver

• Wide spectrum surveillance - typically 30kHz to 50GHz

• Wide dynamic range

• Angle-of-Arrival measurement

• Signal Analysis capability - Pulse width, PRF, scan rate, side-band characteristics, and modulation

• Display

• Recording System - save and analyse data

Electronic Counter Measures

Jamming and deception

• Can be used against enemy sensors - we concentrate on ECM against RADAR

• The basic purpose of ECM is to interfere with the operation of an enemy RADAR system

  • Cause confusion, corrupt information, provide deceptive information

Three basic ways to implement ECM

1. Radiate active signals to interfere with the RADAR - jamming

2. Change the electrical properties of the medium between the target and the RADAR - chaff

3. Change the RCS of the target - stealth

ECM - Jamming

Illuminate the enemy radar with a false signal. This may be in the form of random noise or be a more sophisticated signal designed to provide false information on target parameters such as range and RCS.

• The power of the jammer is crucial. In order to be effective, the ECM transmitter must be capable of emitting enough power in the bandwidth of the victim receiver to mask (jam) its intended signal or to realistically simulate a deceptive signal.

• When an ECM transmitter is used against only one missile, one radar, or one communications device the transmitter can concentrate its available power output into a narrow spectrum.

• If the ECM transmitter operates against several devices separated in frequency, it must spread its available power output over a correspondingly increased spectrum.

Jamming Burnthrough

The range at which its signal is equal to the target return (signal-to-jam ratio = 1)

Important Notes:

• R_J² vs R⁴ is a big advantage for the jammer

• G vs G(θ) is usually a big disadvantage for the jammer. Low sidelobe radar antennas reduce jammer effectiveness.

• Given the geometry, the only parameter that the jammer has control of is the ERP (P_JG_J)

• The RADAR knows it is being jammed. The jammer can be countered using waveform selection and signal processing techniques.

Noise Jamming

A high-power continuous noise signal is transmitted to mask radar echoes.

• The jammer requires large average power – ok on ships but takes up space and weight on aircraft.

• When the radar antenna is pointed toward the jammer, the radar sees signals at all ranges.

• The effect on a PPI scope is to create a solid line at the azimuth of the jammer.

• This line, called a strobe, indicates to the operator that a jammer is present and gives its azimuth, but he does not know the range of the jammer.

• Thus, jamming has the bad effect that it can highlight the target's presence and direction and serve to identify it as hostile, but it has the good effect of denying the radar operator the range of the target.

Spot Jamming

All the power output of the jammer is concentrated in a very narrow bandwidth, ideally identical to that of the radar. Need good ESM to identify operating frequency of radar.

Barrage and Sweep Jamming

Spread their energy over a bandwidth much wider than that of the radar signal.

Used against a number of radars operating at different frequencies

Jamming Tactics

1. Self-screening jammers (SSJ).

   1. In this situation a unit carries jamming equipment for its own protection.

   2. This results in a trade-off between weight and space reserved for ECM equipment and that reserved for sensors, weapons, and fuel.

   3. The trade-off is most critical in aircraft and least critical in ships.

2. Stand-off jammers (SOJ).

   1. Jamming unit remains just outside the range of enemy weapons, providing screening for attacking units that penetrate enemy defences.

   2. The advantage of SOJ is that the jammer is safe from enemy home-on jamming (HOJ) weapons.

   3. The disadvantage is that burn through occurs earlier on the attack units because the jammer must remain at very long range, while the attack units close the enemy to very short range.

3. Stand-forward jammers (SFJ).

   1. The jamming unit is placed between enemy sensors and the attack units.

   2. This situation is most dangerous for the jamming unit because it is a prime target for weapons systems - Home-on-Jam (HOJ) and Anti Radiation (ARM) weapons.

   3. Often unmanned drones are used as SFJ