MiG-29SMT
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The importance of the RCS relies on the fact that it takes part in the radar equation, affecting directly the maximum detection range of a target. The fundamental form of the radar equation is as follows ([17]): 136 Low Observable Principles, Stealth Aircraft and Anti-Stealth Technologies where is the maximum detection range, the transmission power, and the gain and the effective area of the transmitting and receiving antennae (which coincide in the monostatic radar), is the RCS of the target and the minimum detectable signal. Therefore, for given radar parameters , , and , the maximum detection range is proportional to the 4th root of the target RCS: .
In fact, the monostatic or backscatter RCS depends on the following ([18]): Target geometry Target material composition, especially for the surface K. C. Zikidis et al. 137 Position of radar antenna relative to target Angular orientation of target relative to radar antenna Frequency of the electromagnetic energy Radar antenna polarization
1 Shaping The most important factor affecting the RCS is the geometry or the shape of the target, not its size. In order to reduce the RCS, the surfaces and edges should be orientated in such way so as to reflect the radar energy away from an expected radar antenna and not back to it. Considering the flat surfaces (facets) and the acute angles of the F-117, it is understood that it was designed in a way that the expected radar energy would be reflected to irrelevant directions and not back to the emitting radar. The designers tried to avoid any possible surface or edge whose normal vectors would look at a direction where a possible enemy radar might be found, especially for the frontal aspect.
Therefore, in the frame of RCS reduction, all bumps, curves etc should be avoided. In the same way, any external load (pylons, bombs, missiles, fuel tanks, pods) would considerably augment the total RCS. This is the reason why l.o. aircraft carry their armament internally, in special bays. Furthermore, armament bay and landing gear bay doors should close tightly, with no gaps in between. Generally, any irregularity of the surface could incur an RCS increase. Propellers are strictly forbidden, while the first stage engine blades should be carefully hidden inside the intake duct. The whole air intake construction is critical, when designing a low RCS aircraft.
Sharp dihedral corners and parallel surfaces contribute also to the RCS. Therefore, the twin vertical fin empennage, as in the classic F-15E (not the F-15SE), is prohibited. Stealth aircraft have either canted tail fins or no tail fin at all (as in the B-2 Spirit). Regarding existing stealth aircraft, it is also evident that the leading edges of the wings and of the horizontal tail fins (stabilizers) are parallel. This applies to the trailing edges, as well. The aim is always the same: reflect the radar energy to certain, irrelevant directions, and thus keeping the (monostatic) RCS low. Conventional (mechanically scanning) radar antennas should also be avoided, since the antenna itself is an ideal radar energy reflector, increasing the RCS when another radar is looking at it. For this reason, the F-117A carried no radar at all. More recent l.o. aircraft make use of electronically scanned array radars, which offer lower RCS contribution, notably AESA (Active Electronically Scanning Array) radars. Furthermore, these radars should exhibit LPI (Low Probability of Intercept) characteristics, in an attempt to avoid detection by enemy ESM (Electronic Support Measures) systems, trying to detect and locate radar emissions. Apart from the reduction of the aerodynamic drag, which is a positive sideeffect of the absence of external loads, optimizing the aircraft design for RCS reduction is generally incompatible with the aerodynamic principles.
less elements or reflectors of a target less interference paterns in the RCS, thus ventral fins increase RCS
A metasurface based on defect lattices and an alternative physical mechanism, multiwave destructive interference (MWDI), is proposed for ultrawideband radar cross-section (RCS) reduction. The bandwidth of RCS reduction (σR) Is greatly expanded by second destructive interference. The metasurface is composed of 16 basic defect lattices. First, the defect lattice can generate primary destructive interference with the capacity of RCS reduction and amplitude-phase manipulation, which consists of an aperiodic array of square rings with an embedded cross. Second, the interference between multiple backscattered waves produced by the defect lattices at multiple frequencies sampled in an ultrawide band is simultaneously manipulated and optimized by the principle of superposition of waves and particle swarm optimization (PSO) to obtain second destructive interference. The metasurface enables a 10-dB RCS reduction over an ultrawide frequency band ranging from 6.16 to 41.63 GHz with a ratio bandwidth (fH/fL) of 6.76:1 under normal incidence for both polarizations. The estimated, simulated, and measured results are in good agreement and prove that the proposed metasurface is of great significance for bandwidth expansion of RCS reduction.
Ultrawideband Radar Cross-Section Reduction by a Metasurface Based on Defect Lattices and Multiwave Destructive Interference
Wide-band stealth technology is important for many wave-based applications, particularly involving radar, but is held back because expanding bandwidth for radar cross-section reduction is extremely difficult for traditional phase-cancellation methods. This study develops a physical mechanism for...
6.1.2 Flying Wing Flying wing is an ideal stealth shape for aircrafts. It minimizes the number of leading edges, which in turn, reduces radar echo signals.
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