## 4 Conclusions  
A compact frequency reconfigurable antenna is proposed in this paper. Initially, to cover 5G sub--6 GHz band, a wideband triangle-shaped monopole antenna was designed, which was originally inspired from a rectangular monopole antenna. Afterwards, two V-shaped slots were utilized to achieve two notch bands, their length could be adjusted independently to achieve the desire notch bands. Finally, two RF-PIN diodes were inserted at the middle of the slots such that when diodes are in Off-state they active the slot and thus result in notching the band. The overall size of the antenna is 0.19\(\lambda_{o}\)\(\times\) 0.19\(\lambda_{o}\)\(\times\) 0.0081\(\lambda_{o}\), where \(\lambda_{o}\) correspond to the free space wavelength at the lowest resonating frequency. The proposed antenna can operate in wideband mode, two different dual-band modes, or tri-band, depending upon the state of the diodes. Strong agreement between predicted and measured results, along with reasonable gain in passbands and very low gain in the band-stop region, makes the proposed antenna a suitable candidate for 2.1 GHz 4G-LTE band, 2.45 GHz ISM band, 5G-sub-6 GHz band, and S-band applications.  
Conceptualization: A.G., W.A.A., and M.A.; methodology, A.G., N.H. and S.I.N.; software, A.G., W.A.A., N.H., and X.J.L.; validation, A.G., S.I.N., and M.A.; investigation, A.G., W.A.A., S.I.N., and M.A.; resources, M.A., F.F., and E.L.; writing--original draft preparation, A.G., W.A.A., and N.H.; writing--review and editing, X.J.L., B.-C.S., S.I.N., M.A., F.F., and E.L.; supervision, X.J.L., and B.-C.S. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Data Availability StatementData is contained within the article.  
This work is partially supported by RTI2018-095499-B-C31, Funded by Ministerio de Ciencia, Innovacion y Universidades, Gobierno de Espana (MCIU / AEI/FEDER,UE).  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ref.** & **Dimension** **(mm\({}^{2}\))** & **Operational Mode** & **Reconfigurable Technique** & **Frequency Range (GHz)** & **Peak Gain (dBi)** \\ \hline
[5] & 65 \(\times\) 10 & Wideband & N. A & 1.6–2.2 & 2.45 \\
[6] & 25 \(\times\) 30 & Tri-band & N. A & 2.35–5.5 & 3.75 \\
[8] & 100 \(\times\) 100 & Single band & PIN-diode (2) & 2.2–3.8 & 6.5 \\
[9] & 70 \(\times\) 70 & Single band & Varactor (1) & 2.6–3.8 & 5.92 \\
[10] & 50 \(\times\) 50 & Single band & Mechanical & 2–4.5 & 5.6 \\
[11] & 27 \(\times\) 27 & Single band & Varactor (1) & 1.4–2. & 2.48 \\
[12] & 14 \(\times\) 36 & Single band & PIN-diode (2) & 2–2.6 & N.R \\
[13] & 25 \(\times\) 27 & Single and Dual Band & PIN-diode (2) & 2–6 & 2.8 \\
[14] & 20 \(\times\) 16 & Single and Dual Band & PIN-diode (2) & 2–6 & 3.13 \\
[15] & 50 \(\times\) 45 & Dual and Tri Band & PIN-diode (2) & 2.5–5 & 5.8 \\
[16] & 30 \(\times\) 28 & Dual and Quad band & PIN-diode (1) & 1.5–11 & 3.1 \\
[17] & 50 \(\times\) 33 & Wide and Dual Band & PIN-diode (2) & 2–3.75 & 3.2 \\ This Work & 30 \(\times\) 30 & Wide, Dual and Tri band & PIN-diode (2) & 1.8–4.5 & 3.72 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison of the proposed antenna with state-of-the-art works for similar applications.