Stealth radome (SR), especially with an ultra-broad and nearly transparent window between two absorption bands, plays a crucial role in stealth techniques, antenna radomes, and so on. However, current devices have the defects of narrow transmission bands, high insertion loss, and wide transition bands between the transmission and absorption bands, which are unfavorable for the stealth of broadband radar and communication systems. In this paper, a novel SR with an ultra-broad and high-efficiency inter-absorption band transparent window is proposed by combining broadband resonance lumped circuits with a multi-layer cascaded frequency-selective surface (FSS). The equivalent circuit model (ECM) and transmission line method (TLM) are provided and analyzed as a guideline for the SR design. The SR consists of a resistive lossy layer loaded with wide passband lumped circuits and two stacked lossless FSS layers to collectively achieve the high selectivity and ultra-broad transmission band. Simulated results indicate that the proposed SR exhibits an ultra-broad passband from 8.2 to 11.2 GHz (31%) with transmission amplitude more than 0.85 and two 90% absorption bands over 6.8-7.8 GHz and 12-13 GHz, and the transition bands at both sides are only 0.4 GHz and 0.8 GHz, respectively. Our findings can stimulate the promising applications of SR in broadband stealth devices with integrated ultra-broad communication capability or in other electromagnetic (EM) compatibility facilities.

The experimental investigation of supersonic flow over a hemisphere was conducted using Nanoparticle-based Planar Laser Scattering (NPLS) technique in a supersonic quiet wind tunnel at Ma=2.68. Ahead of the hemisphere, boundary layer separation with the formation of a three-dimensional separated flow was observed, which was resulted from the interaction between the three-dimensional bow shock wave and the boundary layer. The complex flow structures of supersonic flow over the hemisphere were visualized. Based on the time correlation of NPLS images, time-space evolutionary characteristics of supersonic flow over the hemisphere were studied, and the evolutionary characteristics of the spanwise and streamwise large scale vortex structures were obtained, which have the features of periodicity and similar geometry. The protuberance is mounted on the surface or flow channel of the supersonic or hypersonic vehicle and the local structure of the flow field will be changed. Currently, achieving flow control has been becoming a research hotspot of supersonic flow. The study of the supersonic plate boundary layer and its interaction with the hemisphere has broad application background and high scientific value. The mutual interference of the hemisphere and supersonic flow generates complex flow field structures, which contain the three-dimensional detached shock wave, the surface topological structure, the circulating region in the downstream, the reattached shock wave and the wake. The complex flow field structures show the characteristics of the supersonic flow over a protuberance on the surface. Therefore the hemisphere can be used as a typical model to study the mechanism of the supersonic flow over a protuberance on the surface, and is also used to verify some questions that are disputed at present, such as the interaction of the three-dimensional curved shock wave and the boundary layer, the effect of the lateral pressure gradient on the surface flow spectrums and the dynamic characteristics of the supersonic vortical structure. Unfortunately, the influences of strong discontinuity and diffusion factors, such as compressibility, turbulence, large scale structure, shock waves and slip line, make it difficult to get the fine structure of supersonic flow over a hemisphere by means of high resolution numerical simulation and measurement. Hawthorne and Martin [1] studied the flow over a hemisphere on the flat plate by means of calculation method in 1955. Zhang [2] studied the interaction of the shock wave and boundary layer about the external flow and internal flow, and provided the photos of typical flow spectrums of different experimental models, including the photos of supersonic flow over a sphere. Some research institutions have studied the typical flow field structures of the supersonic flow over different models by means of experimental and numerical methods at home and abroad, and the models included the cylinder [3][4][5][6][7][8][9][10][11][12][13], the boss [5,6], the blunt fin [5,12], the wedge-shaped obstacle...

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