Kai Li

This work proposes a metasurface capable of achieving a -20dB radar cross section reduction (RCSR) with a relative bandwidth of 123.6%. First, the RCSR performance achieved by introducing phase cancellation and absorption mechanisms within the same frequency band. The focus is on deriving the relationship between the number of non-planar metal ground units and the reduction bandwidth. Second, a circuit analog absorber (CAA) structure is designed to achieve broadband absorption functionality. Additionally, the RCSR performance of the non-planar metal ground with randomly arranged units is analyzed. Finally, by replacing the ground of the CAA with a non-planar metal ground, enhanced scattering performance is achieved. A metasurface prototype is fabricated, assembled, and measured for its reflection performance. The experimental results align well with the simulation results, showing a reduction of more than -20dB from 3.4 to 14.4GHz.

This paper presents an ultra-wideband dual bandpass frequency selective surface (FSS) that exhibits outstanding transmission characteristics and a miniaturization feature in the required frequency band. In order to obtain a dual-band filtering response, initially, a specific topological structure of a dual-band bandpass microwave filter is theoretically investigated and using periodic structures with capacitive, inductive, or resonant-type surface impedances synthesizes its components. Subsequently, employing a compact cascaded hybrid resonant element to construct the FSS, which is composed of convoluted strip grids (CSG), convoluted square rings (CSR), and square rings arranged on different layers. In addition, an accurate equivalent circuit model (ECM) is constructed to analyze the working mechanism of the proposed FSS. Finally, the designed FSS is made and measured. The results indicate that the designed FSS achieved -3 dB bandwidths of 105.4% from 1.01 to 3.26 GHz and 47.8% from 3.75 to 6.10 GHz, respectively. At the center frequency of the first passband, the FSS's size is as compact as 0.056λ ₀ × 0.056λ ₀ . The test results obtained are in good agreement with the results of the full-wave simulation and show excellent resonant stability with respect to different polarizations and incident angles up to 45°.

This work proposes a frequency selective metasurface (FSM) with two transmission windows within the wideband RCS reduction band. First, to achieve dual transmission windows, dual-band and triple-band artificial magnetic conductors (AMCs) are introduced as the two elements of the FSM. Second, the input reactance conditions of the two elements under the reduction condition are derived, and the circuit parameters are optimized to meet these conditions. Furthermore, the transmission and RCS reduction performance after arraying are analyzed based on array theory. Third, based on the corresponding equivalent circuit models, two dual-layer structural elements are designed and arranged in a checkerboard pattern. Finally, a metasurface prototype is fabricated and experimented with. The experimental results demonstrate that the proposed FSM exhibits a -10 dB RCS reduction from 4.2 to 13.9 GHz and transmission windows with insertion losses of -1.45 dB at 7.3 GHz and -1.52 dB at 12.6 GHz.

High-temperature ablation leads to variations in the thickness of the radome during high-speed reentry, consequently impacting the overall performance of the antenna-radome system. This paper develops models of laminar ablation shapes for a typical sphere-cone radome on reentry vehicles caused by laminar ablation during reentry. The main electromagnetic (EM) performance of the radome under different ablation states, including boresight error (BSE) and transmission loss (TL), was calculated using the time-domain finite integration method. The findings indicated that ablation causes significant variations in EM performance. Specifically, BSE exhibits significant fluctuations due to changes in the ablation thickness of the spherical nose, while TL experiences a sharp increase with a higher thickness of conical part ablation. We have redefined the asymmetry of insertion phase shift (IPD), taking into account the influence of the antenna and offering more comprehensive insights on the cause of BSE by conducting analysis on the IPD distribution. This work contributes to the prediction of the EM performance of radomes with laminar ablation during reentry and provides guidance for subsequent compensation measures.

Developing a metamaterial absorber (MA) with both flexibility and temperature insensitivity continues to be a challenge in the field of radar stealth. In this paper, we propose a compensation method for designing flexible and temperature-insensitive MA. This method is revealed through the relationship between the square resistance of the resistive film, the permittivity of the substrate, and the temperature. Importantly, the compensation method is applicable to both the MA in the plane state and the bending state. By utilizing the benefits of the compensation mechanism and the flexible designability of the bilayer cross-shaped structure, the flexible MA proposed in this paper can achieve temperature-insensitive absorption across a broad frequency range. Experimental results indicate that the absorption peaks achieve an absorptivity greater than 90% within the frequency of 7.2–9.4 GHz, exhibiting excellent temperature stability from 25 °C to 300 °C. In comparison to previous studies on flexible MAs, this design offers a distinct advantage in high-temperature environments and provides valuable guidelines for the design of integrated multi-functional absorbers in practical applications.

A design method of five-band polarization-insensitive metamaterial absorber (MMA) based on the slotted structures and the magnetic rubber is proposed for L-, S-, C-, X-, and Ku-band applications. The slotted structures of the top layer, which evolved from two square rings, are used to excite multi-resonance. The range of the electromagnetic (EM) parameters of a magnetic rubber substrate, which is used to adjust the equivalent impedance of the absorber to match the free space impedance in different bands, is estimated using the impedance matching principle. A series of magnetic rubber substrates based on the estimated EM parameters are prepared and measured, whose thickness is only 0.7 mm, meeting the thin design requirements. The absorption of the proposed absorber greater than 90% at 1.7 GHz, 3.87 GHz, 5.96 GHz, 9.4–10.4 GHz, and 14 GHz is achieved when the doping amount of the carbonyl iron powders is 200%. The absorbing performance of the absorber with measured EM parameter agrees well with the theoretical estimates, which validates the accuracy of the proposed design method.

The investigation of how to control the microwave scattering from strong scattering sources has vital applications in military and civilian areas. As a typical target, a rightangle dihedral corner reflector has been extensively investigated because of its strong electromagnetic scattering over a wide observation angle range. In this paper, a right-angle dihedral corner reflector with three loading conditions of the camouflage grass described in our previous investigation is discussed to investigate the radar cross section (RCS) reduction effect for the typical target. For different RCS reduction effects of the camouflage grass loading conditions, which include paste, cover and shield, the calculated results and the measurement results are presented and compared. The loading of camouflage grass greatly reduces the RCS of the corner reflector over a wide angle range at 10 GHz and a broad band from 4 GHz to 18 GHz. The paste loading condition of camouflage grass achieves the best RCS reduction effect. Then, the difference in the monostatic RCS curves is analyzed and explained by multiple scattering effects. The advantages of employing camouflage grass lie in its ability to clearly reduce the RCS of the dihedral corner reflector without shaping the targets or use absorbing materials.