A Low-Profile Self-Stealth Programmable Metasurface with In-Band and Out-of-Band RCS Reduction

Programmable metasurfaces show great application potential in many fields, so studying their radar cross-section reduction (RCSR) characteristics is very important. Metasurfaces based on polarization conversion and artificial magnetic conductors are widely used for RCSR, but they cannot scan beams. Programmable metasurfaces can dynamically steer beams in-band and reduce RCS by changing the phase of electromagnetic waves. But to meet practical needs, they must be stealthy both in-band and out-of-band. This paper presents a low-profile self-stealth programmable metasurface. Self-stealth describes the capability of the metasurface to achieve in-band and out-of-band RCSR through its intrinsic design, without requiring additional structures such as radomes or absorbing materials. The design principle is to achieve out-of-band RCS reduction without increasing the profile height or adding extra radio frequency components. The meta-atom has a positive-intrinsic-negative (PIN) diode to control the in-band (f ₀) x-polarization phase. Switching the PIN diode states gives 1-bit phase modulation. The in-band y-polarization uses a bridge design. Changing the size can get 1-bit phase, and the x- and y-polarizations can be adjusted separately. Also, the top layer has 4 cross-shaped dumbbells and 4 branch structures for out-of-band high (fh ₁) and low (fl ₁) frequencies. The middle layer has four 45° rotated cross-shaped dumbbells and 4 branch structures for out-of-band high (fh ₂) and low (fl ₂) frequencies. So, the meta-atom can modulate phase across 5 frequency bands (fl ₂ < fl ₁ < f ₀ < fh ₂ < fh ₁). The profile height is 0.065λ of the in-band center frequency, which is more conducive to conformal design. A 12 × 12 prototype was made. Simulation and measurement show that the metasurface reduces RCS in 5 bands and its in-band radiation can be used in communication transmission mode, which is good for programmable metasurface technology development.