# New Compact Wearable Metamaterials Circular Patch Antennas for IoT, Medical and 5G Applications
## 5 Active Receiving Compact Double Layer Circular Patch Antennas  
A compact double layer active circular patch antenna is presented in Figure 15. The commercial PHEMT LNA, the same LNA as presented in Section 3, is an integral part of the antenna as presented in Figure 15. The circular patch and the antenna feed network are etched on a substrate with dielectric constant of 2.2 and 1.6 mm thick. The circular resonator diameter is 40 mm. The circular radiator is etched on a substrate with dielectric constant of 2.2 and 1.6 mm thick. The circular radiator diameter is 42 mm. The active antenna configuration is shown in Figure 15. An input matching network matches the antenna to the LNA. An output matching network matches the amplifier output port to the receiver.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**F-GHz** & **S11 dB** & **S11\({}^{\circ}\)** & **S21 dB** & **S21\({}^{\circ}\)** & **S12 dB** & **S12\({}^{\circ}\)** & **S22 dB** & **S22\({}^{\circ}\)** \\ \hline
1.6 & \(-\)12.8 & 134.3 & 18.3 & 123.3 & \(-\)44.2 & \(-\)93.4 & \(-\)18.9 & 113.7 \\
1.8 & \(-\)14.3 & 101.2 & 17.9 & 83 & \(-\)43 & \(-\)86.3 & \(-\)22 & 69.5 \\
2 & \(-\)16.5 & 61.8 & 17.3 & 43.5 & \(-\)40.4 & 94.6 & \(-\)27 & 6.42 \\
2.16 & \(-\)18.5 & 22.1 & 16.8 & 12.9 & \(-\)38 & \(-\)105.5 & \(-\)27.8 & \(-\)70.2 \\
2.4 & \(-\)19.4 & \(-\)53.9 & 15.7 & \(-\)31.8 & \(-\)36 & \(-\)128 & \(-\)22.2 & \(-\)147.2 \\
2.56 & \(-\)17.7 & 99.7 & 15 & \(-\)60 & \(-\)34.6 & \(-\)145.6 & \(-\)19.3 & \(-\)179.4 \\
2.7 & \(-\)15.7 & 131 & 14.3 & \(-\)84.3 & \(-\)33.8 & \(-\)160.3 & \(-\)17.5 & 158.1 \\
2.86 & \(-\)13.7 & 159 & 13.5 & \(-\)111.1 & \(-\)33 & \(-\)177.7 & \(-\)16 & 134.7 \\
3 & \(-\)12.2 & 179.1 & 12.7 & \(-\)134.1 & \(-\)32.4 & 167.4 & 15.2 & 116.3 \\ \hline \end{tabular}
\end{table}
Table 4: High-power amplifier S parameters at the S band.  
Figure 14: S21 of an Active Transmitting Circular Receiving Patch antenna.  
\begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Specification** & **Remarks** \\ \hline Frequency range & 0.4–2.5 GHz \\ Gain & 17.8 dB @2 GHz \\ N.F & 5.5 dB @2 GHz \\ P1 dB & 18.0 dBm @2 GHz \\ OIP3 & 29 dBm @2 GHz \\ Max. Input power & 10 dBm \\ Vgs & 0.48 V \\ Vds & 5 V \\ Ids & 85 mA \\ Supply voltage & \(\pm\)5 V \\ Package & Surface Mount \\ Operating Temperature & \(-\)40 \({}^{\circ}\)C–80 \({}^{\circ}\)C \\ \hline \end{tabular}
\end{table}
Table 3: High-power amplifier (HPA) specification at S band.  
An integral DC bias network supplies the required voltages to the amplifiers. The circular patch antenna S11 parameter on a human body is presented in Figure 16. The active antenna bandwidth is around 30% for VSWR, which is better than 2:1.  
The active antenna gain is around 14 dB at 2.58 GHz and decreases to 10.5 dB at 3.2 GHz. The active antenna S21 parameters, gain on human body, are shown in Figure 17. The active antenna gain is 12 \(\pm\) 2 dB for frequencies from 2.4 to 3.2 GHz. The active circular patch antenna noise figure is 0.6 \(\pm\) 0.2 dB for frequencies from 2.4 to 3.4 GHz, see Figure 18. The antenna matching network, presented in Figure 19a, was optimized to improve the active antenna bandwidth up to 70% for VSWR better than 3:1. Smith chart diagram of S11 with and without the output matching network is shown in Figure 19b. The optimized active receiving antenna S21 parameter, gain on human body, is presented in Figure 20. The active circular patch antenna gain is 13.0 \(\pm\) 3 dB for frequencies ranging from 2 GHz to 4 GHz. There is a good agreement between computed and measured results.  
Figure 16: Double layer active circular patch antenna S11 parameter on a human body.  
Figure 17: S21 parameter on a human body of the Double Layer Active Circular Patch Antenna.  
Figure 19: _Cont_.  
Figure 18: Noise Figure of the Double Layer Active Circular Patch.