# Miniaturized Antenna Array-Based Novel Metamaterial Technology for Reconfigurable MIMO Systems
## 4 Results, Discussion, and Validation  
Now, to validate the proposed antenna array performance experimentally, the proposed array was fabricated using a chemical wet etching process. As seen in Figure 13, the fabricated prototype was presented with maximum dimensions of 50 \(\times\) 30 mm\({}^{2}\). The proposed antenna S-parameters were measured using an HP vector network analyzer. The measured antenna radiation patterns were considered at 3.5, 4, 4.5, 5, and 5.5 GHz inside an RF chamber. This process was invocated after calibrating all processes in the channel using the through calibration technique, and open, short, and 50 \(\Omega\) load. The obtained result from the experimental measurements was evaluated for only two switching scenarios; when all LDR terminals are on and off only. The obtained results are shown in Figure 14 for the two considered scenarios in terms of S-parameters. An excellent agreement between measured and simulated results was found. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Switching Scenario** & **Frequency/GHz** & **Gain/dBi** \\ \hline
0000 & 3–5.5 & 4.5 \\
0011 & 3.5–4.7 & 5.1 \\
1100 & 3.4–4.1 & 6.2 \\
1111 & 3.1–4.6 & 8.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Antenna performance with different switching scenarios. Figure 13: The proposed prototype: (**a**) front view and (**b**) back view. Below, the antenna radiation measurements are presented in Figure 15 at the frequency band of interest. The measurement reveals good agreement between the simulated and measured results. It is good to mention that the presented results of the radiation patterns are for the cases of all LDR switched on and off only. From the obtained results we found that a variation accrues in the antenna directivity due to the surface current change as discussed later. It is good to mention that the antenna measurements were obtained at theta = 0\({}^{\circ}\) and 90\({}^{\circ}\) planes, at which the gain is maximum. Additionally, the maximum E-field can be achieved at theta = 90\({}^{\circ}\) and the maximum H-field can be achieved at theta = 0\({}^{\circ}\). The antenna performance in terms of correlation and diversity envelopes was evaluated experimentally to be compared with the simulated results in Figure 15. The achieved results show insignificant mutual coupling between the antenna elements to realize a maximum correlation factor below 1% with a high diversity of about 99% within the frequency band of interest. This is attributed to the effect of the proposed MTM array reducing the mutual coupling significantly without an effective separation distance. For further analysis, the authors applied a study to realize the MIMO antenna performance in terms of the envelop correlation coefficient (ECC), diversity gain (DG), channel capacity loss (CCL), and total active reflection coefficient (TARC) according to the process that was explained in [23]. As seen in Figure 16, the proposed antenna system realizes a low value of ECC of about 1% with a high diversity of 10 dB over the entire frequency band of interest. This is due to the introduction of the proposed filter design to achieve a maximum mean effective gain (MEG) of about \(-5\) dBi, while the maximum CCL value is about 0.06 bps/Hz for the entire bandwidth. The measured TRAC (at a signal phase difference of 90\({}^{\circ}\) only) was found to be \(-15\) dB, which shows the capability of the proposed MTM inclusions to reduce the correlation factor between the antenna elements. It is good to mention that the evaluated ECC spectrum was obtained from the S-parameters. Figure 14: The measured S-parameters spectra for the proposed antenna array with changing switching scenarios: (**a**) S\({}_{11}\) and (**b**) S\({}_{12}\) spectra. Figure 15: Measured antenna radiation patterns at different frequency bands: **(a)** 3.5 GHz, **(b)** 4 GHz, **(c)** 4.5 GHz, **(d)** 5 GHz, and **(e)** 5.5 GHz. Figure 16: Antenna array performance in terms of ECC, DG, MEG, CCL, and TRAC.