Single-Layer, All-Metallic Metasurface Filter With Nearly 90° Angularly Stable Resonance

We present a method to design a single-layer, all-metallic angular stable metasurface (ASM) filter unit cell for nearly the entire angular spectrum. We formulate the optimization criterion using the energy balance condition derived from Poynting's Theorem. The proposed unit cell has a 'cloverleaf' geometry, and we show that by adjusting the properties of the cloverleaf, we manipulate the in-plane spatial dispersion, thus realizing an angularly stable resonance that extends to nearly 90° incidence. After optimization, we revisit the energy balance criterion and show, using a spatially dispersive admittance expansion, how optimization at three points is enough to obtain the required balance for nearly the entire angular spectrum. The proposed ASM was fabricated from a bare aluminum sheet and measured for transverse electric (TE) and transverse magnetic (TM) polarization, with angularly stable performance that matches the theory and simulation. The proposed design offers new capabilities for radar and antenna design applications, with the simple, single-layer, all-metallic structure being particularly useful in aerospace and satellite applications.