# Compact Four-Port Circularly Polarized MIMO X-Band DRA
## 6 Conclusions  
A four-port CPDRA with compact size was designed and implemented. CP radiation was achieved using the deformed shape of the DR excited with aperture coupled feeding.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Ref** & **No. of Ports** & \(\mathbf{f_{r}(GHz)/BW (\%)}\) & **AR BW (GHz)/(\%)** & **Gain** & **Isolation** & **ESC** & **Antenna Size** \\  & & & & & **(dBi)** & **(dB)** & & **(mm \(\times\) mm)/\(\lambda_{9}\)\({}^{2}\)** \\ \hline
[14] & 2 & 3.45/23.1 & 3.34–4.02/18.5 & 4.83 & \(>\)26 & \(<\)0.02 & 95 \(\times\) 49.7/1.09 \(\times\) 0.56 \\
[16] & 2 & 6.44/36.7 & 7.72–8.08/4.55 & 3.8 & 15 & \(<\)0.05 & 80 \(\times\) 80/1.7 \(\times\) 1.7 \\
[13] & 4 & 3.58/13.1 & 3.54–3.74/4.9 & 5.2 & \(>\)18 & & \\
[13] & 4 & 5.25/6.09 & 5.02–5.18/2.3 & 5.5 & 20 & 0.03 & 80 \(\times\) 80/0.95 \(\times\) 0.95 \\
[10] & 2 & 4/38.5 & 3.58–4.40/20.8 & 6.5 & \(>\)28 & \(<\)0.04 & 350 \(\times\) 350/4.3 \(\times\) 4.3 \\
[25] & 2 & 5.62/21.4 & 5.15–5.88/13.2 & 4.7 & \(>\)18 & \(<\)0.05 & 50 \(\times\) 50/0.92 \(\times\) 0.92 \\
[12] & 2 & 3.42/19 & 3.42–5.36/5 & 6.8 & 16.5 & & \\
[28] & 4 & 5.45/9.4 & 5.45–5.55/ 2 & 4.6 & 16.2 & \(<\)0.05 & 110 \(\times\) 50/1.25 \(\times\) 0.56 \\
[28] & 4 & 3.5/14.4 & 3.34–3.54/5.8 & 4.2 & \(>\)15 & \(<\)0.5 & 66 \(\times\) 60/0.76 \(\times\) 0.70 \\
[29] & 4 & 4.9/5.1 & - & 6.2 & 25 & 0.002 & 140 \(\times\) 45/2.28 \(\times\) 0.73 \\
[30] & 4 & 5.7/10.5 & - & 5 & 18 & 0.25 & 30 \(\times\) 30/0.57 \(\times\) 0.57 \\ This work & 4 & 10.5/38 & 9.2–10.1/9.32 & 6 & \(>\)22 & \(<\)0.005 & 35 \(\times\) 30/1.05 \(\times\) 1.22 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison with other CP MIMO DRAs.  
Figure 21: (a) Total active reflection coefficient (TARC); (b) channel capacity.  
Figure 20: (a) Multiplexing efficiency (\(\eta_{max}\)), and (b) mean effective gain (MEG).  
The study of the single-port CPDRA revealed that a two-port CP antenna could be implemented if a DGS is properly incorporated into the antenna structure. This concept was also applied to implementing a four-port CP antenna. A 10 dB impedance bandwidth of 38% (8.5-12.5 GHz) with a 3 dB AR bandwidth of 9.32% (9.2-10.1 GHz) was achieved. In addition, a gain of 6 dBi was obtained in the band where CP radiation was achieved. The MIMO performance parameters were calculated, and their values remained within the acceptable limits. The suggested antenna could suitably be used in X-band applications.  
Conceptualization, A.A.I. and AM.; methodology, A.A.I., M.I.A., G.V. and A.M.; software, A.A.I., H.Z., S.M.A. and A.M.; validation, H.Z., S.M.A., G.V. and A.M.; formal analysis, H.Z., G.V. and A.M.; investigation, H.Z., S.M.A., M.I.A., G.V. and A.M.; resources, M.I.A., S.M. and A.M.; writing-original draft preparation, A.A.I. and G.V.; writing-review and editing, A.A.I., H.Z., S.M.A., M.I.A., G.V., S.M. and A.M.; visualization, H.Z., S.M.A., M.I.A., G.V. and A.M.; supervision, S.M.A., S.M. and A.M.; project administration, S.M.A., S.M. and A.M.; funding acquisition, S.M.A. and S.M. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The authors declare no conflict of interest.