# New Compact Wearable Metamaterials Circular Patch Antennas for IoT, Medical and 5G Applications
## 3 Active Receiving Compact Circular Patch Antennas  
A general receiver block diagram with an active antenna is presented in Figure 5. A Mini-Circuits TAV541 PHEMT LNA, Low noise amplifier, is an integral part of the antenna as presented in Figures 5 and 6. The circular patch is etched on a substrate with a dielectric constant of 2.2 and 1.6 mm thick. The circular patch antenna diameter is 40 mm. The active antenna configuration is shown in Figure 6. An integral input matching network, that is part of the antenna feed network, matches the circular patch to the LNA as shown in Figure 6. An output matching network matches the amplifier output port to the receiver. The dimensions of the input and output matching network are less than \(20\times 30\) mm and are printed on the same substrate. An integral DC bias network supplies the required voltages to the amplifiers. The amplifier specifications are given in Table 1. The amplifier complex S parameters are listed in Table 2. The amplifier noise parameters are listed in Table 2. The circular patch matched antenna S11 parameter on a human body is presented in Figure 7. The antenna S11 without the matching network is around \(-4\) dB in the frequencies from 2.4 GHz to 3.2 GHz. However, S11 of the antenna with the matching network is better than \(-10\) dB in the frequencies from 2.4 GHz to 3.2 GHz.  
Figure 4: Radiation pattern of the 2.6 GHz circular microstrip antenna with CSRR.  
Figure 3: S11 of the wearable circular microstrip antenna with CSRR.  
The active antenna bandwidth is around 25% for VSWR better than 2:1. Smith chart diagram of S11 with and without the output matching network is shown in Figure 8a. The antenna matching network was optimized, as shown in Figure 8b. The optimized matching network improved the antenna gain by 1.5 dB. The antenna bandwidth was improved to 44% for VSWR better than 3:1. The active antenna gain on human body is around 15 dB at 3 GHz and decreases to 11 dB at 3.6 GHz as presented in Figure 9. The antenna noise figure is better than two for frequencies from 2 GHz to 3.6 GHz. Measurement setups of similar antennas were presented in [2]. There is a good agreement between computed and measured results.  
Figure 5: Receiver block diagram with wearable active antenna.  
Figure 6: Circular Wearable Active Receiving Patch antenna for Medical and 5G Applications.  
Figure 8: _Cont._  
Figure 7: S11 of the Circular patch receiving antenna.  
Figure 8: Circular patch active receiving antenna. (**a**) Smith chart, S11; (**b**) Matching network.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Specification** & **Remarks** \\ \hline Frequency range & 0.4-3 GHz & \\ Gain & 18 dB @2 GHz & Vds = 3 V; Ids = 60 mA \\ N.F & 0.5 dB @2 GHz & \\ P1 dB & 19.1 dBm @2 GHz & \\ OIP3 & 33.6 dBm @2 GHz & \\ Max Input power & 17 dBm & \\ Vgs & 0.48 V & \\ Vds & 3 V & \\ Ids & 60 mA & \\ Supply voltage & \(\pm\)5 V & \\ Package & Surface Mount & \\ Operating Temperature & \(-\)40 \({}^{\circ}\)C–80 \({}^{\circ}\)C & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Low noise amplifier (LNA) specification at S band.  
Figure 9: S21 of an Active Circular Receiving Patch antenna.