# Flexible Antennas for a Sub-6 GHz 5G Band:
## 4 Flexible Antennas for a Sub-6 GHz 5G Band
### Flexible Array Antennas for a Sub-6 GHz 5G Band
#### 4.2.1 Slot/Slit Based Flexible Antenna
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Ref** & \begin{tabular}{c} **Size** \\ **(mm\({}^{3}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Bandwidth** \\ **(GHz)** \\ \end{tabular} & **Gain (dBi)** & **SAR** & **Bending/Effect** &
\begin{tabular}{c} **Substrate**, \\ \(\varepsilon_{r}\), **lan\({}^{\circ}\)**, **lan\({}^{\circ}\)** \\ \end{tabular} & **Advantages** & **Disadvantages** \\ \hline
[29] & \(58\times 78\times 0.9\) & 3.89–5.9 & 3 & - & - & \
\begin{tabular}{c} x-axis and \\ y-axis/Slight \\ variation in resonant \\ frequency \\ \end{tabular} &
\begin{tabular}{c} PET \\ 3.2, 0.022 \\ \end{tabular} & Transparent & Thickness of \\
25 & \(25\times 32\times 0.064\) & \begin{tabular}{c} 2.85–5.35 \\ 2.35–2.5 \\ 3.18–3.82 \\ 4.15–5.42 \\ \end{tabular} & \
\begin{tabular}{c} 3.75 \\ 2.8 \\ 3.5 \\ 3.5 \\ \end{tabular} &
25 & \(25\times 32\times 0.064\) & \begin{tabular}{c} 3.18–3.82 \\ 4.15–5.42 \\ \end{tabular} & \begin{tabular}{c} 2.8 \\ 3.5 \\ 3.5 \\ \end{tabular} & - & \begin{tabular}{c} Bending across \\ - \\ - \\ effect on return loss \\ \end{tabular} & \
\begin{tabular}{c} Ultra-thin \\ Ropers \\ 3.52, 0.003 \\ \end{tabular} & Compact size &
\begin{tabular}{c} Negative gain \\ values at cut-off frequencies \\ \end{tabular} \\ \hline
[48] & \(50\times 50\times 0.088\) & 3.13–4.42 & - & - & - & \begin{tabular}{c} Tensile and \\ compressive bending \\ across different \\ radii/High durability \\ of antenna even after \\ cycles \\ \end{tabular} & - & - & \begin{tabular}{c} Split difference \\ in input \\ 3.5, 0.022 \\ 100 bending \\ \end{tabular} & \begin{tabular}{c} Split difference \\ in input \\ 3.5, 0.022 \\ 3.5 \\ \end{tabular} & \begin{tabular}{c} Split difference \\ in input \\ 3.5, 0.022 \\ 100 bending \\ \end{tabular} & \begin{tabular}{c} Split difference \\ in input \\ 3.5, 0.022 \\ 100 bending \\ \end{tabular} & \begin{tabular}{c} Split difference \\ in input \\ 3.5, 0.022 \\ 100 bending \\ \end{tabular} & \begin{tabular}{c} Split difference \\ in input \\ 3.5, 0.022 \\ 100 bending \\ \end{tabular} & \begin{tabular}{c} Split difference \\ in input \\ 3.5, 0.022 \\ 100 bending \\ \end{tabular} & \begin{tabular}{c} Split difference \\ in input \\ 3.5, 0.022 \\ 100 bending \\ \end{tabular} & \
\begin{tabular}{c} Split difference \\ in input \\ 3.5, 0.022 \\ 100 bending \\ \end{tabular} &
\begin{tabular}{c} Split difference \\ in input \\ 3.5, 0.022 \\ 100 bending \\ \end{tabular} \\ \hline
[50] & \(20\times 32\times 0.1\) & \begin{tabular}{c} 2.38–2.79 \\ 3.27–4.05 \\ 4.80–8.44 \\ \end{tabular} & \begin{tabular}{c} 0.65 \\ 2.26 \\ 2.6 \\ 4.80–8.44 \\ \end{tabular} & \begin{tabular}{c} Bending across \\ 1.92–5.5 GHz \\ 2.6 \\ 100 (9 tissue) \\ \end{tabular} & \
\begin{tabular}{c} E-plane and \\ bending across \\ different radii/Slight \\ difference in \\ resonance for \(\pm\) plane \\ bending \\ \end{tabular} &
\begin{tabular}{c} LCP \\ 2.9, 0.002 \\ 2.9, 0.002 \\ \end{tabular} & Low antenna & Low gain \\ \hline
[51] & \(70\times 70\times 0.11\) & 2.038–3.745 & \begin{tabular}{c} 3 (2.45 GHz) \\ 5 (3.42 GHz) \\ (10 g tissue) \\ \end{tabular} & \begin{tabular}{c} 0.98 (foucar) \\ 0.782 (meest) \\ - \\ Polylimide \\ 3.5, 0.002 \\ \end{tabular} & - & \
\begin{tabular}{c} Kapton \\ radiation \\ efficiency, \\ highly flexible \\ \end{tabular} &
\begin{tabular}{c} Good \\ \\ structure \\ \end{tabular} \\ \hline
[52] & \(55\times 40\times 0.125\) & 1.77–6.95 & 2.5–5.9 & - & - & \begin{tabular}{c} Bending across \\ different radii/Stable \\ performance \\ \end{tabular} & \begin{tabular}{c} Kapton \\ 3.5, 0.007 \\ 3.5, 0.007 \\ \end{tabular} & \
\begin{tabular}{c} Simple \\ configuration \\ 3.5, 0.002 \\ \end{tabular} &
\begin{tabular}{c} Variation in \\ measured results \\ due to material \\ specifications \\ \end{tabular} \\ \hline
[53] & \(60\times 60\times 1.52\) & \begin{tabular}{c} 2.40–2.54 \\ 3.38–3.52 \\ 3.35–3.52 \\ \end{tabular} & 6.7 & \begin{tabular}{c} 0.2 and 0.1 \\ (2.45 GHz) \\ 6.7 \\ 3.38–3.52 \\ \end{tabular} & \begin{tabular}{c} x- and y-axis bending \\ (1.96 tissue) \\ 8.7 \\ 8.9 \\ \end{tabular} & \begin{tabular}{c} \\ radio/ \(\Delta\) negligible \\ shift in frequency \\ (3.45 GHz) for 10 g \\ \end{tabular} & \
\begin{tabular}{c} Felt/Tac \\ 2.2, 0.0099 \\ \end{tabular} &
\begin{tabular}{c} Good gain and \\ efficiency \\ \end{tabular} & Less conformal \\ \hline
[55] & \(30\times 33\times 0.1\) & \begin{tabular}{c} 2.52–2.62 \\ 3.31–3.64 \\ 3.31–3.64 \\ \end{tabular} & \begin{tabular}{c} 2.39 (2.60 GHz) \\ 1.75 (9.48 GHz) \\ \end{tabular} & - & \begin{tabular}{c} Across different \\ radii/No significant \\ change in antenna \\ performance \\ \end{tabular} & \
\begin{tabular}{c} Polymimide \\ 3.5, 0.002 \\ 3.5, 0.002 \\ \end{tabular} & Low volume &
\begin{tabular}{c} Radiation \\ pattern not \\ stable \\ \end{tabular} \\ \hline
[56] & \(37\times 31\times 0.1\) & \begin{tabular}{c} 3.4–3.78 \\ 5.7–6.9 \\ \end{tabular} & - & - & - & \begin{tabular}{c} Bending across \\ different degrees/30\({}^{\circ}\) \\ bending showed \\ triple band variation \\ triple band variation \\ \end{tabular} & \begin{tabular}{c} LCP \\ 2.9, 0.0025 \\ 2.9, 0.0025 \\ \end{tabular} & \
\begin{tabular}{c} Conformal \\ due to the low \\ thickness of the substrate \\ \end{tabular} &
\begin{tabular}{c} Complex \\ fabrication \\ \end{tabular} \\ \hline
[57] & \(86\times 86\times 0.1\) & \begin{tabular}{c} 3.1–3.9 \\ 5.4–6.2 \\ \end{tabular} & \begin{tabular}{c} 9.078 \\ 3.4–6.65 \\ (With \\ reflector) \\ \end{tabular} & \begin{tabular}{c} 0.0833 (5.5 GHz) \\ (1 \(\beta\) of tissue) \\ \end{tabular} & \begin{tabular}{c} Ropers UL- \\ (1 \(\beta\) of tissue) \\ \end{tabular} & \
\begin{tabular}{c} LPM \\ (1 \(\beta\) of tissue) \\ \end{tabular} &
\begin{tabular}{c} Improved \\ gain, reduced \\ SAR \\ \end{tabular} & Large volume \\ \hline
[60] & \(14\times 3.25\times 3.25\) & \
\begin{tabular}{c} 5.4–5.9 \\ 3.25 \\ \end{tabular} &
\begin{tabular}{c} 4.3 (5.8 GHz) \\ 4.3 (5.8 GHz) \\ tissue) \\ \end{tabular} & - & Fabric & Good gain & Low bandwidth \\ \hline \hline \end{tabular}
\end{table}