Dual Stop Band and Narrow Pass Band FSS Structure for Shielding Sub-6 GHz 5G Band Signals and Reduce EMI to Radio Altimeter

In this paper, an efficient approach is proposed to achieve shielding of sub-6 GHz 5G band n77 (3.3-4.2 GHz), n78 (3.3-3.8 GHz), and n79 (4.4-5 GHz) signals to prevent interference with radio altimeters operations (4.2-4.4 GHz) in Aeronautical Radio-Navigational Services (ARNS) band. In this paper two designs are proposed, one on a low-cost FR4 substrate and the other on a low loss Taconic TLY-5 substrate. The proposed FSS structure on TLY-5 substrate offers a narrow pass band response at 4.3 GHz with a 200 MHz bandwidth (BW) and an insertion loss (IL) of -0.5 dB for satisfactory radio altimeter operations (4.2-4.4 GHz), along with band stop response at 3.74 GHz with 50 dB shielding and at 4.53 GHz with 39.5 dB shielding. The FSS structure on FR4 substrate offers a narrow pass band response at 4.3 GHz with -3 dB insertion loss (IL) along with a band stop response at 3.74 GHz with 31.5 dB shielding and at 4.62 GHz with 24.5 dB shielding. The proposed FSS unit cell contains a square loop patch with 8 axe arms attached to it. This unit cell design is printed on 0.8mm substrate thickness. The proposed FSS structure is symmetrical and provides a stable angular response up to 60° of incidence for both the transverse electric (TE) mode and the transverse magnetic (TM) mode. To validate the design, a prototype of the proposed FSS structure is fabricated on FR4 Substrate and its results obtained were compared with simulation results. Both simulated and measured results were in congruence with each other.