Abstract
In this paper, we propose an electrically small antenna consisting of a composite right/left-handed (CRLH) transmission line (TL) and a non-Foster matching circuit. An interdigital capacitor (IDC) and spiral inductor are used to fabricate the very high frequency (VHF) band antenna based on CRLH TL. The size of the proposed antenna is as small as 0.025 × 0.014 × 0.0008 λ at 145.5 MHz using the zeroth-order resonant generated by the CRLH TL. The antenna operation bandwidth is extended by the non-Foster circuit (NFC) consisting of a pair of transistors in a cross-coupled manner. An antenna prototype is fabricated and the input impedance, the received power, and gain of the proposed antenna are measured. The results show that the broadband characteristic is maintained while the form factor is extremely small compared to the wavelength. The average received power enhancement and increased bandwidth of antenna are 17.3 dB and 335.5 MHz (from 249.2–268.2 to 145.5–500 MHz), respectively. The calculated gain of the proposed antenna with the non-Foster is about −45 dBi at 155 MHz. The proposed antenna can be considered as a potential candidate of a low-profile antenna for military ground communications at the VHF band.
Highlights
For the military very high frequency (VHF) ground communication system, a conventional monopole or dipole antenna is mainly used. It guarantees reasonable gain for reliable wireless communications despite its long length (e.g., 0.5–5 m at VHF band) since the physical size of the antenna is proportional to the wavelength
In our previous work [9], we proposed a composite right/left-handed (CRLH) transmission line (TL)‐based VHF antenna with operating‐frequencies from to 164.4 aMHz
The extracted parameters of the CRLH TL unit cell using a pseudo‐inverse technique are shown in Table 2 [27]
Summary
For the military very high frequency (VHF) ground communication system, a conventional monopole or dipole antenna is mainly used It guarantees reasonable gain for reliable wireless communications despite its long length (e.g., 0.5–5 m at VHF band) since the physical size of the antenna is proportional to the wavelength. The non-Foster circuits have not been used for the matching of the small VHF antennas using the CRLH TL. We applied a non-Foster circuit to the CRLH TL-based VHF antenna to resolve issues by the miniaturization such as bandwidth narrowing and receive power mitigation. The measured 10-dB return loss bandwidth of the proposed antenna system was 145.5–500 MHz (354.5 MHz), which is 18 times wider than the CRLH TL antenna without the non-Foster circuit applied. The received power was measured outdoors and an average of 17.3-dB enhancement was displayed in the frequency range of 120–500 MHz
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