# Cascaded Frequency Selective Surfaces with Matryoshka Geometry for Ultra-Wideband Bandwidth
## 3 Measurement Setup  
With the FSSs manufactured and prepared, the setup for the experimental measurements of FSSs used the microwave measurement laboratory of the Telecommunications and Applied Electromagnetism Group of the Federal Institute of Education of Paraiba (GTEMA-IFPB), shown in Figure 8, with a two-port VNA E5071C network analyzer and Pasternack Enterprise PE9859-20 horn antenna.  
FSSs were placed on acrylic holders measuring 20 cm\({}^{2}\) with different thicknesses of from 2 mm, 3 mm, and 5 mm. They were placed in a measurement window to minimize reflection and deflection issues. The measurement window is made of an 80 \(\times\) 60 cm\({}^{2}\) plane of aluminum with a 20 \(\times\) 20 cm\({}^{2}\) vent in the middle with small holes to screw and secure the FSS and acrylic holders, allowing the signal to travel between a horn antenna placed 1.5 m from the measurement window to the other side, passing through the vent with  
Figure 6: Cascaded FSS on measurement window.  
Figure 7: Acrylic supports used for spacing between FSSs.  
the FSS. Other signals that hit the measurement window are deflected, not reaching the other horn antenna, also placed 1.5 m from the measurement window. With this device, it is possible to analyze the response of the FSS to a planar incident wave polarization, as well as to its incidence angle \(\varphi\), as shown in Figure 9, in which the window is horizontally rotated according to the desired angle. Measurements of the frequency response of the cascaded FSSs were conducted separately, with the band-reject FSS superimposed and with different gaps between the FSSs, as shown in Figure 10. Finally, reference measurements of the environment were conducted to analyze the results.  
Figure 8: Photograph of the experimental setup.  
Figure 9: Setup spatial coordinates on the FSS to identify the horizontal and vertical polarizations.  
The method of each measurement was repeated so that the FSS frequency response was measured at angles from 0 to 45\({}^{\circ}\) in 15\({}^{\circ}\) intervals to analyze the stability of the frequency response in relation to the angle variation. The plates were also measured in horizontal \(x\) and vertical \(y\) polarizations of the transmitting antenna and finally, in the case of the cascaded FSS configuration, measurements were conducted with the spacing between plates varying incrementally from 3 mm to 20 mm to analyze the behavior of the frequency response.  
It is possible to minimize the influence of external factors, such as environmental conditions or manufacturing imperfections. A printing machine is used to manufacture and affix the printed design on the plate to avoid imperfections in the unit cells. To minimize environmental factors--such as reflections and diffractions of the signal waves on objects around the setup, the interference of external signals that reach the room, the edge effect when the signal waves hit the corners of the FSS, and other influences of the environment--reference measurements are used for the experimental results. These reference measurements are obtained with a setup without any FSS in the measurement window, and this way, it is possible to measure the environmental influence on the setup. This procedure is repeated for each incident angle and then used to normalize the frequency responses presented in this article.