# A Low-Profile HF Meandered Dipole Antenna with a Ferrite-Loaded Artificial Magnetic Conductor
## 1 Introduction  
NVIS (near-vertical-incident-signal) communication is a method of communicating using the characteristics of radio waves reflected from the ionosphere [1]. The high-frequency (HF) band does not pass through the ionosphere and is reflected from the ionosphere [2]. Due to these characteristics, one advantage of the HF band is that communication is possible without satellite equipment or additional facilities on the ground, and with this advantage, the HF band can be used on rugged terrain and for military communication. However, the size of the antenna operating on the HF band is inevitably bulky because the size of the antenna is inversely proportional to the operating frequency [3]. Due to this constraint, the HF band antenna cannot easily be utilized on a moving object for which mobility and aerodynamics are important, such as a vehicle. Therefore, various miniaturized HF antennas have been proposed to be mounted on vehicles [4, 5, 6, 7, 8, 9, 10, 11, 12]. In one study [4], the performance of a monopole antenna operating on the HF band was verified; the height of this antenna was up to 0.18 \(\lambda_{L}\) (\(\lambda_{L}\) is the wavelength of the lowest operating frequency in free space). A monopole antenna with a height of 0.04 \(\lambda_{L}\) operating on the HF band has also been proposed [5]. In another study [6], an antenna with a height of 0.005 \(\lambda_{L}\) reduced by applying a two-arm configuration was proposed. A multi-turn loop structure was applied to a dipole antenna and an antenna with a height of 0.01 \(\lambda_{L}\) was introduced [7]. Also, a miniaturized antenna that combines multi-turn loops has been proposed; the height of this antenna was 0.018 \(\lambda_{L}\)[8]. Researchers have also introduced an inverted-F antenna with a height of 0.04 \(\lambda_{L}\)[9], but previously proposed antennas in general remain too tall with bandwidths that are too narrow. An artificial magnetic conductor (AMC) is applied as a means by which to realize broadband characteristics while ensuring low-profile characteristics [13, 14]. The AMC is a type of metamaterial, and the phase of the reflected wave in a specific frequency bandis identical to the phase of the incident wave such that low-profile characteristics of the antenna can be realized [15]. In addition, the impedance matching of the antenna can be improved, implying that it is possible to implement broadband characteristics [16]. The AMC can be equivalently analyzed with the parallel circuits with the capacitance and inductance [17]. The operating frequency and operating frequency band of the artificial magnetic conductor are determined by the inductance and capacitance values [18]. Considering the operating frequency and the operating frequency bandwidth of the AMC, it is advantageous for AMC to have a high inductance value [19]. The inductance value of the AMC is determined by the height or permeability of the AMC. However, it is not practical that increasing the height of the AMC to achieve high inductance value considering applicability. Therefore, studies have been conducted to increase the inductance value of the AMC by loading the material [20,21]. With these characteristics, an artificial magnetic conductor and an artificial magnetic conductor-based antenna operating on the HF band were proposed [22]. In the present study, a low-profile HF meandered dipole antenna with a ferrite-loaded AMC is proposed. First, a miniaturized unit cell of the AMC which operates on the HF band is designed by loading a highly-permeable ferrite material. To designed the compact dipole antenna, a meander structure is applied. Among the currents in the folded element of the meandered dipole antenna, the currents developed in the opposite direction are offset from each other [23]. Through this, capacitive reactance and inductance reactance are canceled mutually, so that the meandered dipole antenna can operate at a lower frequency than a linear dipole antenna with the same area [24].