Using an Equivalent-Circuit Model to Design Ultra-Wide Band-Stop Frequency-Selective Surface for 5G mm-Wave Applications

In this work we propose a system of two frequency-selective surfaces (FSSs) with an ultra-wide band-stop response for 5G millimeter-wave applications. The analyses are based on the equivalent circuit method, which predicts the transmission characteristics for a plane wave with normal and oblique incidence, and the scattering matrix technique, which provides the result of the cascaded structure. The geometries used in the single-layer FSSs are simple to design, and a series of basic equations are described in order to calculate the inductance and capacitance of conducting strips. FSSs prototypes were fabricated and measured in an anechoic chamber. The first FSS is shaped with the four-arms star geometry, which has a resonant frequency at 27.92 GHz for both measured and simulated results. The second FSS is based on the quasi-square geometry, whose resonant frequency for the experimental and numerical results are 35.68 GHz and 35.76 GHz, respectively, for the transverse electric polarization. These two single-layer FSSs present theoretical resonant frequency at 28 GHz (FSS #1) and 35.8 GHz (FSS #2). Cascading of the two FSSs was realized by using an air gap whose effect was analyzed. A gap space in the order of about
$\lambda /4$
matched with the predicted resonant frequency of the individual structures. Numerical and measured results show excellent agreement with a maximum error of 1.03%. All measured results closely follow those of simulated ones, thus validating the design approach and applications.