Design of Transparent Frequency Selective Surface on Window Glass for 5G Indoor Communications

In this letter, a transparent frequency selective surfaces (FSSs) applied on window glass with two different substrates for spatial filter selectivity of 5G mm-Wave indoor communications is proposed and experimentally evaluated. The proposed FSS based on cross-dipole unit is designed with a cascading structure on a PET layer, which allows to achieve bandpass filter in electromagnetic wave incidents range from 0° ~ 45° in the n257 and n258 bands (24.25 to 29.5 GHz). Furthermore, the proposed FSSs on window glass is cheap and universally applicable to building window by using commercial glass as a substrate for FSS while aesthetically transparent. Therefore, trade-off relationship between the area of the FSS and optical transparency is analyzed. Two different dielectric materials, conventional glass ( \(\:\text{C}\text{a}\text{s}\text{e}1:{\:\epsilon\:}_{r}=7.38\:and\:\text{t}\text{a}\text{n}{\delta\:}=0.06\) ) and borosilicate glass (Case2: \(\:{\epsilon\:}_{r}=4.6\:and\:\text{t}\text{a}\text{n}{\delta\:}=0.0037\) ), have been used as a substrate to compare the transmission response with different dielectric constant and loss tangent condition. For performance evaluation, insertion loss was measured at 1.30 dB (Case1), 1.94 dB (Case2) and optical transparency was measured at 61.99% (Case1), 64.77% (Case2). Our proposed FSSs are good candidates for signal-selective applications at mm-Wave with high optical transparency on window glasses.