# Constraints of Using Conductive Screen-Printing for Chipless RFID Tags with Enhanced RCS Response
## 5 Measurement  
The simulated results of the common substrate manufactured as well as the conductive printed transponders were verified by the monostatic measurement of the RCS response in an anechoic chamber; see Figure 12.  
Figure 11: Simulated RCS of IC U-dipole coupled in the metallic loop sensor tag.  
Figure 10: Sketch of IC U-dipole coupled in the metallic loop sensor tag.  
The double ridge horn antenna DRH 20 [37] was used for measurement because of the reflection coefficient from which the resulting RCS response was evaluated with the help of the one-port Formula (8). The measured transponders were situated at a distance of 500 mm in front of the antenna. The RCS response of the tag was calculated using relations given by [33] as  
\[\sigma^{tag}=20 log\Big{|}\frac{S_{11}{}^{tag}-S_{11}{}^{iso}}{S_{11}{}^{ref}-S_ {11}{}^{iso}}\Big{|}\sigma^{ref}, \tag{8}\]  
where \(S_{11}{}^{tag}\) is the reflection coefficient when the measured tag is used as a scatterer. In turn, \(S_{11}{}^{ref}\) symbolizes the reflection coefficient when a reference metallic plate is used as a scatterer. Next, \(S_{11}{}^{iso}\) represents the reflection coefficient of the antenna itself when no scatterer is installed and comprises residual reflection from the experiment environment. Finally, \(\sigma^{tag}\) is the RCS of the measured tag, while \(\sigma^{ref}\) is the RCS of the reference scatterer, which is a rectangular metal plate with the dimensions of a \(\times\) b = 60 \(\times\) 60 mm\({}^{2}\) and a thickness of 0.3 mm. The analytical formula for the reference scatterer RCS is given by [35] as  
\[\sigma^{ref}=4\pi\frac{a^{2}b^{2}}{\lambda^{2}}, \tag{9}\]  
where \(\lambda\) is the signal wavelength in free space.  
The measured RCS of the above-presented structures manufactured by screen-printing on Folanorm polyester film and paper substrate compared to the standard copper-on-microwave substrate technology is depicted in Figures 13-16. It can be seen that in the case of a large array of resonators, the individual resonance drops are degraded; however, in the case of a small number of bits (e.g., in the case of sensor transponders; see Figure 16), this degradation is still readable and acceptable for the specific purpose. The frequency shift of the peaks/drops in comparison with the \"copper on substrate\" realization is caused by the effective permittivity difference. The screen-printed versions of the tags have unchanged dimensions and the geometry of the motif.  
Figure 12: Monostatic measurement setup in anechoic chamber with detail of IC U-dipole coupled in the metallic loop sensor tag.  
Figure 14: Measured RCS of re-arranged U-slots in the metallic plate tag manufactured by the screen-printing technology on Folanorm polyester film and a paper substrate compared to a standard copper-on-microwave substrate technology.  
Figure 13: Measured RCS of shorted re-arranged U-dipole tag manufactured by the screen-printing technology on Folanorm polyester film and a paper substrate compared to a standard copper-on-microwave substrate technology.  
Figure 15: Measured RCS of an array of detuned planar dipoles closely coupled to a rectangular metallic plate manufactured by the screen-printing technology on Folanorm polyester film and a paper substrate compared to a standard copper-on-microwave substrate technology.