November 13, 2015

Ultrathin coating can defeat ultrahigh frequency microwave radar for more stealthy fighter jets

A group of scientists from China may have created a stealth material that could make future fighter jets very difficult to detect by some of today’s most cutting-edge anti-stealth radar.

The researchers developed a new material they say can defeat microwave radar at ultrahigh frequencies, or UHF. Such material is usually too thick to be applied to aircraft like fighter jets, but this new material is thin enough for military aircraft, ships, and other equipment.

Today’s synthetic aperture radar use arrays of antennas directing microwave energy to essentially see through clouds and fog and provide an approximate sense of the object’s size, the so-called radar cross section. With radar absorbent material not all of the signal bounces back to the receiver. A plane can look like a bird.

Their proposed absorber is almost ten times thinner than conventional ones.

They proposed and fabricated an ultra-thin broadband AFSS absorber with an ST pattern for UHF applications. Based on the TL model, the resonance frequency and real part of input impedance are given as functions of loaded and distributed parameters. With ST coefficients of x = y = 1, the tunability and strong absorption are concisely demonstrated. The calculated results suggest that the varactor modulates the imaginary part of the input impendence, producing the tunability, while the resistor mainly adjusts real part, producing the strong absorption. Applying various ST coefficients to the unit cell pattern, they found that a small x/y effectively expands the tunable bandwidth. The measured reflectivity of the proposed absorber covers a broad band of 0.7–1.9 GHz below −10 dB, and the total thickness 7.8 mm is only ∼λ/29 of the center frequency. As radar detection equipment continues to improve, their thin absorbers with broad bandwidth and working in the UHF band will be widely useful.



Journal of Applied Physics - An ultra-thin broadband active frequency selective surface absorber for ultrahigh-frequency applications



At frequencies below 2 GHz, conventional microwave absorbers are limited in application by their thickness or narrow absorption bandwidth. In this paper, we propose and fabricate an ultra-thin broadband active frequency selective surface (AFSS) absorber with a stretching transformation (ST) pattern for use in the ultrahigh-frequency (UHF) band. This absorber is loaded with resistors and varactors to produce its tunability. To expand the tunable bandwidth, we applied the ST with various coefficients x and y to the unit cell pattern. With ST coefficients of x = y = 1, the tunability and strong absorption are concisely demonstrated, based on a discussion of impedance matching. On analyzing the patterns with various ST coefficients, we found that a small x/y effectively expands the tunable bandwidth. After this analysis, we fabricated an AFSS absorber with ST coefficients of x = 0.7 and y = 1. Its measured reflectivity covered a broad band of 0.7–1.9 GHz below −10 dB at bias voltages of 10–48 V. The total thickness of this absorber, 7.8 mm, was only ∼λ/54 of the lower limit frequency, ∼λ/29 of the center frequency, and ∼λ/20 of the higher limit frequency. Our measurements and simulated results indicate that this AFSS absorber can be thin and achieve a broad bandwidth simultaneously.

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