Metasurfaces are ultrathin, two-dimensional structures composed of periodic or quasi-periodic arrays of sub-wavelength scatterers. They possess the unique ability to comprehensively control the phase, amplitude and polarization of incident electromagnetic waves with added advantages such as ease of fabrication and less space consumption. On account of these factors, they are progressively replacing their three-dimensional counterparts, i.e. metamaterials in a wide gamut of fields such as signal multiplexing, stealth technology, holographic imaging, planar optical devices, polarization transformation devices and so on. Further, metasurfaces offer a strong and promising platform for aerospace applications due to their diversified functionalities and reduced weight penalties. Moreover, it has been widely used for the realization of thin, broadband and polarization independent radar absorbing structures (RAS). In this regard, this paper presents a concise review on the recent advancements in the field of metasurfaces specifically for stealth applications. Special emphasis has been laid on diffusion and coding metasurfaces due to their attractive properties towards the realization of low observable platforms. Furthermore, various types of metasurfaces as well as the different techniques used for the optimization of metasurfaces are also described in detail.

A multi-layered graded porous airborne nose-cone radome design for radar antenna system with surveillance and tracking capabilities at X and K bands, respectively, is presented. The radome wall structure has five layers and is symmetrically constructed with the dielectric constant increasing gradually from the outer layer to the middle layer on either side. The inner layers are made up of silicon nitride with varying porosity for attaining variable dielectric parameters, whereas the outermost layers are composed of quartz lamination for better impedance matching. The analysis shows that the proposed radome design gives excellent EM performance characteristics in the EM window regions at both X and K bands. The novel dual-band radome design presented has potential application in airborne radar antenna system incorporating both surveillance and tracking capabilities.

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