## 3 Multiple Reconfigurable Features in Antenna
### Frequency, Radiation Pattern, and Polarization Reconfigurable Antennas  
None of the above designs provide more than one or two reconfigurable features. In the literature there is only one design, proposed in [85], for independently three-parameter reconfiguration. In [86], another design of frequency, radiation pattern, and polarization reconfigurable antenna was proposed, but with limitations in terms of tuning, and, unlike the design in [85], it cannot provide simultaneous, independent reconfiguration. This is a major research gap, albeit a much harder challenge to design an antenna with the flexibility to reconfigure all its fundamental properties in terms of frequency, radiation pattern, and polarization. In the following, the design of [85] is explored. Figure 8: The configurations of the (**a**) designed and (**b**) fabricated pattern and polarization reconfigurable antenna [82]. Reproduced with permission from [82], Copyright IEEE, 2018. Figure 9 shows the antenna schematics and the prototype [85], a patch antenna radiator and a parasitic pixel surface with 66 pixels and 60 PIN diodes. It is the switched-grid pixel surface that enables the antenna to be reconfigured simultaneously in frequency, radiation pattern, and polarization. Different configurations of the switches tune the frequency of operation from 2.4-3 GHz. The antenna radiation pattern can be steered between \(\pm 30^{\circ}\), and its polarization can be reconfigured between LHCP/RHCP and LP. The design is suitable for different mobile and wireless communication systems. Table 1 provides a comparative summary of recently proposed reconfigurable antenna types published in the literature. Fundamental characteristics in terms of antenna type, reconfiguration type and the number of the employed switches, operation frequency, and the overall size of the antennas are provided and have been compared. This is intended to help readers to determine what types of reconfigurable antennas are most suitable for their applications. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**References** & **Antenna** & **Reconfiguration** & **Reconfiguration** & **Frequency** & **No. of** & **Antenna** \\  & **Type** & **Type** & **Means** & **(GHz)** & **Switches** & **Size (mm)** \\ \hline
[14] & Monopole & Frequency & PIN-Diode & 1.77–2.51 & 4 & 50 \(\times\) 120 \\
[15] & Slot & Frequency & PIN-Diode & 1.73–2.28 & 2 & 50 \(\times\) 80 \\
[21] & Patch & Bandwidth & PIN-DiMEMS & 2–4 & 8 & 12 \(\times\) 12 \\
[23] & Slot & Bandwidth & PIN-Diode & 1.64–2.68 & 6 & 10 \(\times\) 64 \\
[31] & DRA & Rad. Pattern & PIN-Diode & 5.8 & 8 & 50 \(\times\) 50 \\
[32] & Patch & Rad. Pattern & PIN-Diode & 2.45 & 8 & 95.5 \(\times\) 100 \\
[37] & Bow-Tie & Polarization & PIN-Diode & 1.3–1.85 & 4 & 58 \(\times\) 58 \\
[40] & Patch & Polarization & PIN-Diode & 2.1–2.6 & 24 & 60 \(\times\) 60 \\
[48] & Monopole & F/B & PIN/varactor & 3.9–4.82 & 3 & 25 \(\times\) 75 \\
[52] & Monopole & F/B & PIN/varactor & 0.72–3.44 & 4 & 65 \(\times\) 120 \\
[53] & Monopole & F/B & PIN-Diode & 3.4–8/4.7–5.4 & 4 & 70 \(\times\) 70 \\
[59] & Patch & F/R & varactor Diode & 2.15/2.25/2.38 & 2 & 151.5 \(\times\) 160.9 \\
[62] & Slot & F/R & PIN-Diode & 3.6/3.95 & 2 & 30 \(\times\) 40 \\
[63] & Slot & F/R & PIN-Diode & 1.8/1.9/2.05 & 14 & 130 \(\times\) 160 \\
[69] & Monopole & F/P & varactor Diode & 1–1.6 & 112 & 88 \(\times\) 114 \\
[72] & Patch-Slot & F/P & PIN-Diode & 2.4/3.4/4.1 & 2 & 60 \(\times\) 65 \\
[74] & Monopole & F/P & PIN-Diode & 1.9–2.7 & 2 & 40 \(\times\) 70 \\
[76] & Patch & F/P & varactor Diode & 2–3.1 & 1 & 100 \(\times\) 100 \\
[79] & PFA & R/P & PIN-Diode & 2.5 & 1 & 50 \(\times\) 50 \\
[81] & Slot & R/P & PIN-Diode & 5 & 36 & 78 \(\times\) 78 \\
[82] & Helical & R/P & PIN-Diode & 0.9 & 32 & 81 \(\times\) 81 \\
[85] & Patch & F/R/P & PIN-Diode & 2.4–3 & 60 & 31 \(\times\) 31 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparative summary of reconfigurable antennas described in the literature. Figure 9: Schematic of the multi-functional reconfigurable antenna [85].