## 5 Conclusions  
An electrically small antenna consisting of a composite right/left-handed transmission line and a non-Foster matching circuit was proposed. In order to manufacture an electrically small antenna, a unit cell composed of an IDC and spiral inductor was designed. The CRLH TL antenna was fabricated by connecting three unit cells to obtain CRLH characteristics. The size of the proposed antenna was as small as \(0.025\ \lambda\ \times\ 0.014\ \lambda\ \times\ 0.0008\ \lambda\) at 145.5 MHz using the zeroth-order resonant generated by the CRLH transmission line. The non-Foster circuit that could generate negative capacitance was designed by cross-coupled-junction transistors. By checking the load impedance and the transient response in the time domain, we confirmed the stability of the non-Foster matching circuit. By using the non-Foster matching circuit in the CRLH antenna, the bandwidth was increased by 335.5 MHz and the average received power was enhanced by 17.3 dB. In addition, the calculated gain using Friis'  
Figure 19: Measured and simulated gain of the antenna (note: “w/o Non-Foster” indicates the antenna was matched using ordinary passive matching technique).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Reference** & **Antenna Size** & **Bandwidth** & **Substrate** \\ \hline
2015 [10] & \(22\times 30\times 0.8\ \text{mm}^{3}\) & 4 GHz (2.6–6.6 GHz) & \\  & \(0.21\lambda_{0}\times 0.29\lambda_{0}\times 0.008\lambda_{0}\) @2.9 GHz & 87\% & \\ \hline
2015 [11] & \(20.4\times 6.8\times 0.8\ \text{mm}^{3}\) & 1.5 GHz (5.8–7.3 GHz) & RO4003 \\  & \(0.39\lambda_{0}\times 0.13\lambda_{0}\times 0.015\lambda_{0}\) @5.8 GHz & 23\% & \\ \hline
2017 [12] & \(21.5\times 30\times 0.8\ \text{mm}^{3}\) & 6.8 GHz (1.8–8.6 GHz) & RO4003 \\  & \(0.372\lambda_{0}\times 0.52\lambda_{0}\times 0.014\lambda_{0}\) @5.2 GHz & 120\% & \\ \hline
2018 [13] & \(23\times 17\times 1.6\ \text{mm}^{3}\) & 6.02 GHz (0.48–6.5 GHz) & Duroid 5880 \\  & \(0.037\lambda_{0}\times 0.027\lambda_{0}\times 0.0026\lambda_{0}\) @0.48 GHz & 172.49\% & \\ \hline
2018 [14] & \(17.5\times 32.15\times 1.6\ \text{mm}^{3}\) & 7.05 GHz (0.85–7.9 GHz) & FR-4 \\  & \(0.204\lambda_{0}\times 0.375\lambda_{0}\times 0.018\lambda_{0}\) @3.5 GHz & 161.14\% & \\ \hline proposed antenna & \(31.4\times 23.7\times 1.6\ \text{mm}^{3}\) & 0.153 GHz (0.14–293 GHz) & \\  & \(0.014\lambda_{0}\times 0.01\lambda_{0}\times 0.0007\lambda_{0}\) @0.14 GHz & 70.3\% & FR-4 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison table with CRLH antennas.  
transmission formula at our target frequency was increased by more than 15 dBi. We note that the received power and gain improvements were measured and evaluated instead of the absolute gain and radiation efficiency due to the limitations of the measurement facility at the VHF band. Nevertheless, the improvements by applying the non-Foster circuit were clearly demonstrated using these relative parameters. The proposed antenna system can be considered as a potential candidate of a low-profile receiving antenna for military ground communications at the VHF band.  
The present work was conducted in cooperation with all authors. [PERSON], [PERSON] and [PERSON] analyzed the problem and performed numerous simulations; [PERSON], [PERSON], [PERSON], [PERSON]-H.L., [PERSON]-[PERSON], [PERSON] and [PERSON] contributed to the conceptualization, fabrication, and measurement; [PERSON], [PERSON] and [PERSON] wrote a draft which was edited by all co-authors. All authors have read and agreed to the published version of the manuscript. This research received no external funding.  
This work has been supported by the Future Combat System Network Technology Research Center program of Defense Acquisition Program Administration and Agency for Defense Development. (UD190033 ED). The authors declare no conflict of interest.