Miniaturized Near All-Angle Stable 2.5-D FSS for Dual-Band Shielding in Transmission Mode and Multiband Absorption in Reflection Mode

Frequency selective surface (FSS) gains significant interest in the wireless communication system for shielding against electromagnetic interference (EMI). This article presents a novel multiband 2.5-D FSS with dual operations in the transmission and reflection modes. The FSS exhibits dual-band bandstop filtering in transmission mode to shield EMI at sub-6-GHz 5G, WLAN and WiMAX frequencies. In the proposed multilayer geometry, two stopband (SB) resonances (at 2.32 and 4.04 GHz) are generated using enhanced capacitance loaded modified Jerusalem cross (EC-MJC) and via connected meandered square loop (VC-MSL). FSS transmits the signal with a low insertion loss of <0.6 dB at passband frequency (2.98 GHz) existing between two reflection bands. The miniaturized unit cell size (
$ < 0.07~\lambda \text{L}$
), polarization insensitive, and highly stable filter response at almost all incidence angles (up to 80°) are the attractive features of the designed FSS. In reflection mode, the 2.5-D FSS has been configured for multiband microwave absorbers at dual, triple, and quad-band resonances. The FSS and absorber are practically realized for the experimental validation of simulation results. The measured results are in good accordance with the numerical simulation for both operating modes, which establishes the design principle of the multifunctional FSS (MFSS).