At present, stealth technology has been widely used in various aircraft, missiles, tanks, warships, submarines and ground military installations. The core of stealth material stealth technology is to reduce the radar cross section (RCS) to produce low visibility (L0). The use of absorbing materials and the selection of appropriate shapes and structures are the most effective methods to achieve stealth.
1. Definition of RCS
The technical definition of the target's radar cross section: the area of an imaginary total reflector of electromagnetic waves that is the same as the energy reflected by the actual target to the definition of the radar transmitting and receiving antenna RCS.
2. The influence of shape on RCS
To reduce the radar reflection area, the first thing to do is to reduce the impact area of the ship’s side projection, simplify the superstructure, and avoid the large vertical plane intersecting the horizontal plane at right angles. At all corners, the joints should be as smooth as possible. The shape design technology has a great influence on reducing the reflection area of the radar, which can reach about 30% of the total reduction. For example, the superstructure of the DDG51-class destroyer in the United States is generally enclosed, and the superstructure and side have a certain slope, and a large number of composite materials are used as radar wave absorbing materials. The Kirov-class cruisers of the former Soviet Union designed the outer wall of the superstructure into many small inclined planes, and the aircraft carrier was equipped with very thick absorbing materials. The British Type 23 frigate has adopted comprehensive stealth measures. In the future, with the development of stealth hull design technology, ships with new hull structures may appear.
3. Test characterization technology
RCS is a physical quantity that characterizes the intensity of electromagnetic scattering waves of a weapon system. Measuring this physical quantity is to measure the scattered field. It is carried out under the condition that the target is illuminated by a plane wave and the radar receiving antenna receives the spherical wave scattered by the far field. The target must be located on the radar transmitting antenna. In the far field. This test technique is used to study how to reduce the target RCS. Main methods: full-scale outdoor static measurement, microwave darkroom measurement, compact field measurement, etc. The outdoor static measurement field is suitable for measuring RCS of large targets. The target to be measured can be full-scale aircraft, missiles, tanks, etc., both real objects and models. Its main disadvantage is that it is restricted by climatic conditions, it cannot be measured when encountering bad weather, such as strong wind, and it is disturbed by the surrounding terrain. Microwave anechoic chamber is an indoor measurement place, which is not restricted by weather conditions. The indoor walls are covered with absorbing materials to simulate the situation of free space. The microwave anechoic chamber used in the early period was a rectangular anechoic chamber, and the wedge-shaped anechoic chamber was developed later. The predetermined measuring frequencies of the two are different. As the name implies, compactness can shorten the far-field distance, and can change the spherical electromagnetic wave output by the radiation source into a plane electromagnetic wave within a limited distance. Both microwave frequency and millimeter wave frequency can be used. Targets of appropriate size at these frequencies can achieve near-field focusing.In addition to the static test field mentioned above, there is also a dynamic test field that can provide the operating conditions of the target under test.It is a kind of radar composed of multiple types and widely distributed. In order to promote the research of stealth technology, various countries are establishing various far-field, near-field, dynamic and static test bases, large-scale radar cross-section test fields, and microwave anechoic chambers for testing complex-shaped targets. And reduce the signal characteristics of weapon systems to provide experimental means, creating good conditions for the development of stealth weapons.