Conformal frequency selective surface metamaterial for 5g mm-wave EMI shielding and antenna applications

Abstract

The Frequency Selective Surface (FSS) metamaterials are a periodic array of artificial structures that can selectively filter or control electromagnetic (EM) wave transmission and reflections based on their frequency. FSSs find applications in a wide range of fields, including wireless communication systems, electromagnetic interference (EMI) shielding, antenna design, reflectors, and EM wave manipulation. The state-of-the-art research shows that metal shields, conductive paints, and Coatings are widely used to protect sensitive RF devices from EMI; however, they block all EM waves. On the other side, FSS reduces the EMI by blocking only specific frequencies and allowing the propagation of undesired frequencies. Conformal FSS is desirable due to its low profile, ease of fabrication, and conformal integration capabilities. Another significant application of FSSs is antenna performance enhancement like gain and isolation. The high gain is required for 5G mmWave band application to overcome the free space path loss. The highly isolated multiple input multiple output (MIMO) antenna elements also increase the antenna performance through the radiation pattern deflection by metamaterial. Therefore, designing the conformal miniaturized stopband FSSs for the 5G mmWave band is highly desirable with high stopband stability and low shifting of peak transmission zero (TZ) frequency at high oblique incident angle (OIA), and polarization insensitivity, which can provide effective EMI shielding at desired frequency band. This research aims to design three new miniaturized conformal FSSs for 5G mmWave multiband, dual-band, and single-band applications and analyze their applications for EMI shielding and antenna performance enhancements. Firstly, a new triple-band stopband conformal FSS is designed for the 5G mmWave (n257, n258,n259, and n260) band. Interconnected square split ring resonators achieve the peak TZ attributes at 27.09 GHz, 38.71 GHz, and 41.81 GHz frequencies, with stopband bandwidths (BW) percentages of 14.58%, 8.27% and 7.8%, respectively, for Transverse magnetic (TM) polarized EM waves. The periodicity of the unit cell is 0.4 λₒ, where λₒ is the wavelength of the lower stopband frequency. Secondly, a miniaturized polarization insensitivity conformal dual-band FSS for 5G mmWave (n257 and n260). Two back-to-back resonators are separated with a 0.254 mm thin dielectric substrate. The stopband BW% are 42.8% at 28 GHz and 24.2% at 38 GHz. The periodicity of the unit cell is 0.26 λₒ, and the key features of the designed FSS include a miniaturized unit cell structure with an OIA stable filter behavior up to 60°. Finally, a thin, flexible single-band FSS is designed for 5G n257 band applications. The ultra-miniaturized unit cell is completed by fractal technology and the periodicity of the unit cell is only 0.154λₒ, which leads to a high stability of stopband at OIA up to 60°. The simulated results of the FSSs are validated by measurement of the fabricated prototype, and both results agree well, which leads to the designed FSSs as potential candidates for EMI shielding and antenna performance enhancement.