# A New Concept of Reconfigurable Antenna Structure Based on an Array of RF-MEMS Switches
## 4 Numerical and Experimental Assessment
### Experimental Assessment  
Concerning the scattering parameters, a set of on-wafer measurements has been carried out. The experimental setup is reported in Figure 11. The prototype has been characterized through Ground-Signal-Ground (GSG) probes connected to a Vector Network Analyzer (VNA). A gold ground plane of thickness \(t_{g}=100\)\(\upmu\)m has been placed below the prototype structure. The first set of measurements aims to measure the impedance of microstrip lines of different widths obtained by activating rows of the matrix as in the first numerical experiment. The goal of this first set of measures is to confirm the simulated data reported in Table 1. The comparisons between numerical and experimental results are summarized in the following Table 2. It can be seen that the measurements are in good agreement with the simulation, and the maximum error is 11.0%. The error is probably due to the measurement procedure that used small needles to connect the prototype sections. However, the results obtained can be considered quite satisfactory.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Rows** & **Columns** & **Thickness [\(\upmu\)m]** & **Impedance [\(\Omega\)]** \\ \hline
1 & 7 & 430 & 54.75 \\
2 & 7 & 1030 & 35.82 \\
3 & 7 & 1630 & 25.42 \\
4 & 7 & 2230 & 18.21 \\
5 & 7 & 2830 & 12.68 \\
6 & 7 & 3430 & 10.34 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Reconfigurable structure set as microstrip of different widths.  
Figure 10: Simulation of different rectangular antenna patches obtained by properly connecting the gold pads.  
The next set of measurements aims to verify the prototype's capabilities as a reconfigurable patch antenna. The structure has been set as a rectangular antenna patch by activating four of the seven columns characterized by a resonance frequency \(f_{7\times 4}=17.0\) GHz. The patch antenna's \(S_{11}\) has been measured with the vectorial network analyzer and considering the experimental measurement setup shown in Figure 11. The results are reported and compared with the numerical data in Figure 12, as it can be noticed that the measured resonance frequency is \(f_{m}=17.5\) GHz 500 MHz higher with respect to the simulated data. The observed gain of the antenna is approximately 5 dB within the frequency range of 16 GHz to 18 GHz. The frequency shift is probably due to the considered experimental measurement setup since the connection between VNA and patch antenna has been done with suitable conductive tips, as shown in Figure 11. The next measurement considers the structure with all the seven columns activated, corresponding to a square patch of dimension \(5230\times 5230\)\(\upmu\)m\({}^{2}\) and a resonance frequency of \(f_{7\times 7}=8.0\) GHz. Also, in this case, the measures are compared with the numerical data and reported in Figure 13. Also, in this case, the measured resonance is \(f_{7\times 7}=8.6\) GHz, 600 MHz higher than the simulated data. A similar frequency shift has been observed for all the other configurations. Each element of the rectangular patch antenna demonstrates a gain of approximately 2 to 3 dB, exhibiting linear polarization. However, variations in antenna performance occur at higher frequencies and under different switching configurations. It is noteworthy that the performance parameters can be optimized, indicating a potential for enhancement when the prototype is employed as a reconfigurable antenna.  
Figure 11: Photo of the experimental measurement setup.  
Figure 12: Simulated vs. experimental measurement for a \(7\times 4\) rectangular patch configuration.