# Quad Element MIMO Antenna for C, X, Ku, and Ka-Band Applications
## 4 Simulated Time-Domain Analysis  
Since the proposed antenna is wideband in nature, it is important to check its time domain characterization. Important time domain characteristics like group delay, phase response, and isolation analysis by keeping the antenna in face-to-face (FTF) and side-to-side (STS) orientation are studied. The two similar antennas are placed in two different configurations maintaining 300 mm, which are depicted in Figure 11.  
Figure 11: Simulated time-domain analysis in the layout: (**a**) Face to Face and (**b**) Side to Side.  
Figure 12 shows the group delay (GD), magnitude of the S21, and phase of S21. From Figure 12a,b, it is clear that the group delay lies between 1010 and 1085 ps; however, the S21 dB was below \(-75\) dB over bandwidths OFB1, OFB2, and OFB3. The S21 phase is shown in Figure 12c-e, showing the linear features within all the desired wideband operations in both FTF and STS layouts.  
Figure 12: Simulated results at the different layout: (**a**) Group delay, (**b**) S21 (dB), (**c**) S21 (degree) over OFB1, (**d**) S21 (degree) over OFB2, and (**e**) S21 (degree) over OFB3.  
In order to discuss the time-domain analysis, the fidelity factor of antenna and system fidelity factor play a crucial role. The antenna fidelity factor (FF) is obtained by calculating the cross-correlation of the radiated E-field and the input signal; however, the system fidelity factor (SFF) is calculated by the cross-correlation between the transmitted pulse and the received pulse. The simulated value of FF and SFF are calculated in two different orientations (face to face and side by side), by keeping the proposed antenna 300 mm apart. Here the Gaussian sine pulse is given as input to the Tx port in order to find the FF and SFF. The obtained value of FF and SFF is presented in Table 2.  
The antenna's compact dimensions impact its transient behavior, and the level of pulse distortion is considered acceptable (SFF \(>\) 0.5 [54; 55]), which is suitable for use in impulse-type UWB systems.  
Table 3 indicates the recently reported literature comparison, in which the literature [8; 9; 13] covers the WLAN band and only [8] covers the n77/n78/n79 5G NR band. Here the proposed MIMO covers n77/n78/n79 5G NR band, WLAN, Wi-Fi, and wide band mm-Wave. None of the reported antennas in Table 1 calculates the CC, which is essential for investigating MIMO performance. The proposed MIMO system computed the CC in operating bands, which is quite suitable for investigated bands.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Orientation** & **FF** & **SFF** \\ \hline face to face & 0.9359 & 0.7584 \\ \hline side by side & 0.9477 & 0.7583 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Simulated value of FF and SFF.  
\begin{table}
\begin{tabular}{l l l l l l l l l l l l} \hline \hline
**Ref** & **Bands** & **No. of Perss** & **Antema Size/Substrate** & **Peak Gain** & **Peak Efficiency (\%)** & **Isolation (dB)** & **ECC** & **TARC** &
\begin{tabular}{l} CC cut (\(-20\,\)dB)** \\ SNDs [bp/s/s] \\ \end{tabular} \\ \hline  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline Ref & **Bands** & **No. of Ports** & **Antenna Size/Substrate** & **Peak Gain** & **Peak Efficiency (s)** & **Isolation (dB)** & ECC & TARC & \multicolumn{1}{c}{CC (at \(-\)20.48)} \\  & & & & & & & & & & \\
[59] & single band & 3.4-3.6 GHz (6-dB) & 8 & 0.233 \(\times\) 0.145 \(\times\) 0.003\(\lambda_{\lambda}^{1.5}\) & 2.85\(\prime\) dB & 65 & \(>\)12 & \(<\)0.2 & - & 38 \\  & & & & (PRR) & & & & & & \\
**This work** & **triple band** & **3-77 GHz (10 dB)** & 4 & **1.097 \(\times\) 1.087 \(\times\) 0.083\(\lambda_{\lambda}^{1.5}\)** & 3.89 \(\prime\) dB & 58.5 \(\prime\)22 & \(<\)0.04 & \(<\)\(-\)7.48 & 16.6-19.2 \\  & & **35.5-49.4 GHz (10 dB)** & **(PRR)** & **59.21 dB** & **52.5** & \(>\)22.37 & \(<\)0.04 & \(<\)\(-\)4.59 dB & 16.9-18.4 \\ \hline \hline \end{tabular}
\end{table}
Table 3: _Cont._