Radar technology paper-radar passive jamming technology
Abstract: The false targets and radar decoys in radar passive jamming technology are analyzed. It is discussed that reducing the cross-sectional area of target radar is an important radar passive jamming technology. Two main methods of radar passive jamming are pointed out, namely reflector jamming and chaff jamming.
Keywords: passive jamming electronic countermeasure radar corner reflector
China Library Classification Number: TD367 Document Identification Number: A Document Number:1009-914x (2016) 04-0027-01.
introduce
Passive electronic interference refers to the interference caused by the reflection or absorption of electromagnetic waves by equipment that does not emit electromagnetic waves to electronic equipment. Also known as negative interference. According to the nature of action, it can be divided into repressive passive interference and deceptive passive interference. According to the principle of interference, it can be divided into reflective passive interference and absorption passive interference. Reflective passive jamming is to use equipment with good reflection characteristics to throw it in a large area to form strong interference clutter and cover up the target echo signal; Or throwing or laying reflective devices intermittently to form false targets and deceive electronic devices. Absorbing passive jamming is to coat the target with radio wave absorbing materials, convert the electromagnetic energy irradiated on the target into other forms of energy as much as possible, and minimize the reflected electromagnetic energy, so that the echo signal of the target received by electronic equipment is greatly weakened, resulting in a serious decline in the detection ability of electronic equipment to the target; Or, on the light wave propagation path between the photoelectric equipment and the target, extinction aerosol such as absorption smoke screen and water mist is cast to prevent the photoelectric equipment from detecting and tracking the target. Commonly used radar passive jamming equipment mainly includes chaff, corner reflector, Lombard lens reflector, false target, radio wave absorbing material and air suspension. This paper mainly discusses radar passive jamming technology.
1. radar passive jamming technology
1. 1. False targets and radar decoys
A reflector used to deceive the radar. They produce false target information to radar, which is one of the effective countermeasures to destroy the target selection, tracking and killing of enemy air defense systems. It is mainly used for the penetration of aircraft and strategic weapons and the self-defense of aircraft and ships. False targets and radar decoys are different in use and performance. False targets are usually used to deal with the warning command radar of enemy air defense systems. Generally, they are complex in structure, realistic in performance, equipped with engines, and can fly independently, such as rocket-type false targets and unmanned aircraft. Radar decoys are often used against airplanes and ships. False targets launched or dropped in order to destroy the tracking system of radar or missile actually make the tracking system of radar or missile track radar bait. There are three types of radar decoys: rocket radar decoys, towed radar decoys and throwing radar decoys. The requirements for false targets and radar decoys are that their radar cross-sectional areas must be equal to or larger than the real targets, and they have the same speed characteristics and echo jumping characteristics as the real targets.
1.2. Reduce the radar cross-sectional area of the target.
Radar relies on the echo of the target to find the target. Therefore, reducing the radar cross-sectional area of the target can reduce the reflection of the target on radar waves. This is a basic radar countermeasure technology. Correctly designing the shape of the target and adopting composite materials with high strength, low specific gravity and radar echo absorption can significantly reduce the radar cross-sectional area. The method to further reduce the radar cross-sectional area of the target is to coat the surface of the target with microwave absorbing materials, so that the signal received by the radar is weakened, or even the echo signal is not received, and the detection distance of the radar is shortened. This kind of coating is called radar-proof coating. According to the different electromagnetic wave absorption principles, radar-proof coatings can be divided into four types. (1) absorbing coating: radar waves do not reflect when hitting the target coated with this material, and most or all of the energy is absorbed by the coating. ② Interference coating: The reflected wave entering the coating and reflected by the target surface and the reflected wave directly reflected by the coating surface interfere and cancel each other, so that the total radar echo is zero. (3) Resonant coating: It includes many absorption units, and the electrical parameters and dimensions of each unit are adjusted to make it resonate with the frequency of incident electromagnetic waves, thus seriously attenuating the incident electromagnetic waves. (4) Radioisotope coating: coating radioactive substances on the target to ionize the local space near the surface of the target to form a plasma screen capable of absorbing electromagnetic waves.
2. Radar passive jamming equipment
The technology of using the reflection, scattering, refraction and absorption of electromagnetic waves by equipment that does not produce electromagnetic radiation to change the echo characteristics of radar and destroy and hinder the detection and tracking of enemy radar, also known as passive jamming technology. The advantages of radar passive jamming are small size, light weight, simple manufacture, low price, convenient use and strong adaptability, which can effectively jam radars with multiple frequencies and polarizations in different directions at the same time. The common equipment for radar passive jamming includes chaff, reflector, bait, radar bait and microwave absorbing material.
2. 1. chaff interference
Foil refers to interference wire, interference piece and interference rope (tape). Usually, it is a strip cut from metal foil, metal-plated medium (commonly nylon wire and glass wire plated with aluminum, zinc and silver), or directly made of metal wire. Chaff jamming is to put a large number of randomly distributed metal reflectors in space to produce secondary radiation jamming radar.
There are two main types of chaff jamming: one is suppression jamming, that is, a large number of chaffs are put into a certain atmospheric space to form an interference corridor covering the fleet. This kind of interference forms a strong chaotic echo similar to noise on the radar screen, so it can cover up the target echo; The other is deceptive jamming, that is, when aircraft and ships are tracked by radar, chaff is dropped to form a false target, which makes the radar track chaff jamming group many times stronger than the echo of aircraft and ships, and makes the aircraft and ships get rid of radar tracking.
The length and diameter (or width) of the chaff must be selected to ensure the most effective reflection of electromagnetic waves in a wide frequency range. Therefore, the length of chaff widely used is about half the wavelength of the interfered radar, which is usually called half-wavelength oscillator (also called dipole). This is because the half-wavelength oscillator resonates with electromagnetic waves (in fact, chaff resonates with electromagnetic waves, and the length of the half-wavelength oscillator is slightly shorter than that of the interfered radar), and the reflection is the strongest and the radar cross-sectional area is the largest. What is the average radar cross-sectional area of a single half-wave chaff oriented horizontally in the air? /2=0.32? 2。 The average radar cross-sectional area of a single half-wavelength chaff (or a processed short half-wavelength chaff) randomly oriented in the air is:? /2=0. 17? 2。 Radar cross-sectional area is only related to wavelength? Yes, the width and thickness of chaff are only to meet the needs of mechanical strength, manufacturing technology and aerodynamics.
Foils are usually made into fixed packages (bags or bundles), and the number of foils in each package depends on the radar cross-sectional area of the covered target and the interference band. In order to interfere with the enemy's radar coverage of their own targets, the total radar cross-sectional area of each package of chaff should be larger than that of the covered targets. The half-power bandwidth of a single half-wavelength chaff is equivalent to 10% ~ 15% of its resonant frequency, which is very narrow for radar interference. In fact, many thin half-wavelength chaffs with different lengths are mixed and packaged or put into a plurality of chaff packages, and each chaff package corresponds to a different frequency band to obtain a large bandwidth. You can also use chaff as long as several meters to tens of meters (several times the wavelength of the interfered radar) to increase the bandwidth and achieve the purpose of jamming radars in various frequency bands.
In order to effectively jam any polarized radar, it is required that the chaff dropped by air should be randomly oriented. In fact, because of their different lengths, materials and shapes, chaffs have their own motion characteristics in the atmosphere. The uniform and short half-wavelength gap is basically horizontally oriented and rotates downward in the air. This chaff has a strong jamming effect on horizontally polarized radar and a weak jamming effect on vertically polarized radar. The motion law of long chaff or treated short chaff in air may be completely random. Due to the influence of aircraft turbulence, short chevs may be completely random at the first launch, and they can effectively interfere with radars of various polarizations.
2.2 reflector
There are corner reflectors, Lambert lens reflectors and Van Gogh reflectors that produce strong radar echoes with decoys. Atta reflection array, radar reflection balloon, etc.
Corner reflector: a reflector consisting of three metal planes intersecting each other vertically, which can be divided into triangle, square and circular corner reflectors (Figure 1). The corner reflector can reflect the incident electromagnetic wave three times in a larger angle range, and then reflect it back in the original incident direction (Figure 2), resulting in a strong echo. Small-sized corner reflectors also have large radar cross-sectional areas. The maximum radar cross-sectional area mainly depends on the accuracy of keeping right angles between reflecting surfaces. Small angle deviation and uneven board surface will greatly reduce the radar cross-sectional area. The pattern of corner reflector is about 25? ~50? . Triangular corner reflector is widely used because of its wide and flat pattern, high interface stiffness and low manufacturing requirements.
Lambert lens reflector: It is made by plating metal on the local surface of Lambert lens. According to the size of the metal-plated reflective surface, there are 90? 、 140? 、 180? Division of reflectors. Rumber lens is a dielectric sphere with layered structure. The dielectric constant of its outer layer is close to that of air, and it increases towards the center of the sphere. The parallel electromagnetic wave beam irradiated on the lens surface is focused on a point in the spherical metal reflecting surface by the medium, reflected by the metal reflecting surface, and then returned to the direction of the emission source through the medium, so it has a large radar cross-sectional area and good directivity and frequency characteristics. The pattern width of Lambert lens is about 90? 、 140? 、 180? , in which 140? The left and right characteristics are the best.
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