A Metasurface-Based Flexible Triple Bandpass Filter in ISM, IoT and Cellular 5G Wearable Applications

This article presents a single-layered metasurface (MS)-based slot type triple bandpass filter with low insertion loss and sharp roll-off performances. Jeans is selected as substrate material, having a relative permittivity of 1.68; thereby making the design wearable in nature. The proposed structure's unit cell comprises mainly three shapes of slots viz., an outer rectangular ring, an inverted U-shaped slot along with three rectangular extensions on 3 sides. The filter exhibits three distinct transmission peaks at 2.54 GHz, 4.52 GHz and 5.74 GHz, respectively, making it suitable for operations in the ISM, IoT and sub-6 GHz cellular bands, having substrate dimension in the order of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.24 \lambda_{0} \times 0.24 \lambda_{0}$</tex> where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\lambda_{0}$</tex> is wavelength correspond to the lower band. Further, the proposed filter exhibits two stop bands between the transmission frequencies and can be helpful for wearable applications. The 3-dB transmission bandwidths of the wearable filter have been computed as 1.07 GHz, 0.56 GHz and 1.15 GHz, respectively. The electric field distributions at the transmission peaks have been studied to understand the roles of the various slots in the final design. The proposed design has been subjected to angular stability analyses to find the structure angularly stable up to an incident angle of 45°.