# Quad-Band Uniformly Spaced Array Antenna Using Diverse Patch and Fractal Antennas
## 4 Discussion  
In this paper, a quad-band uniformly spaced array antenna is proposed. For multi-band functionality, diverse element antennas such as bow tie fractal patch antennas, fat bow tie fractal antennas, fat bow tie antennas, and square patch antennas are used to operate at 2.45/3.7/4.3/5.0 GHz. The modified Sierpinski fractal antenna is firstly proposed, and three other element antennas were suggested by previous studies. The ratio of the resonant frequencies is 0.486 with similarly sized element antennas. Table 3 shows the performance of other multi-band shared-aperture antennas. With previous shared-aperture antenna technology, it is difficult to increase the number of frequency bands and improve array disposition. In this study, four frequency bands are achieved, compared to two or three frequency bands in other studies. In addition, each disposition of four array antenna is uniform 2 \(\times\) 2 in contrast to the other studies, which had irregular arrangements for different frequency bands. The proposed antenna also presents performance enhancements in terms of port isolation and antenna gain. It is observed that mutual coupling between two elements is sufficiently low, at below \(-\)23 dB. The proposed array antenna exhibits good characteristics for impedance matching and obtains peak antenna gain from 11.1 dBi to 14.4 dBi. The concept of this proposed antenna can be applied to multi-band base-station antenna systems and sensor applications for military applications.  
**Author Contributions:** Author Contributions: Conceptualization, I.K. and E.K.; methodology, I.K. and E.K.; software, I.K.; validation, I.K.; formal analysis, I.K.; investigation, I.K.; resources, I.K.; data curation, I.K.; writing--original draft preparation, I.K.; writing--review and editing, E.K.; visualization, I.K.; supervision, E.K.; project administration, E.K. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
Figure 11: Comparison of normalized radiation patterns using full-wave simulation and array analysis at port 1 and port 2 (\(\phi=0\)°).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference \#** & \begin{tabular}{c} **Frequencies** \\ **(GHz)** \\ \end{tabular} & \begin{tabular}{c} **Array** \\ **Disposition** \\ \end{tabular} & \
\begin{tabular}{c} **Port Isolation** \\ **(dB)** \\ \end{tabular} &
\begin{tabular}{c} **Gain** \\ **(dB)** \\ \end{tabular} \\ \hline
[3] & 2.94–2.96/9.8–9.98 & 4 \(\times\) 8/1 \(\times\) 2 & \(>\)25.3 & 18.3/9.5 \\
[4] & 5.0–6.2/7.2–8.9 & 2 \(\times\) 2/4 \(\times\) 4 & \(>\)15/20 & 14.5/17.5 \\
[5] & 1.07–1.24/8.3–10.3 & 1 \(\times\) 1/8 \(\times\) 8 & \(>\)17/20 & 7.0/23.0 \\
[6] & 3.12–3.4/2.9–2.9–36 & 1/12/elements & \(>\)25 & 8.5/11 \\
[7] & 5.84–5.94/2.77–25.48 & 2 \(\times\) 2/1 \(\times\) 2 & \(>\)38/55 & 10/11.85 \\ This study & 2.44–2.45/3.69–3.72/ & 2 \(\times\) 2/2 \(\times\) 2/ & \(>\)23.2 & 11.1/13.5/ \\  & 4.35–4.41/5.02–5.09 & 2 \(\times\) 2/2 \(\times\) 2 & \(>\)23.2 & 13.8/14.4 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Frequencies, array disposition, port isolation, and gain of shared aperture array antennas.