# A Low-Profile Ferrite Dipole VHF Antenna for Integrated Mast Applications
## 2 Antenna Design  
Figure 1a presents an illustration of the 3-D view of the proposed antenna, which consists of a ferrite dipole, a ground plane, and a loop-type feeding structure. The overall size of the ferrite dipole is 0.0636 \(\times\) 0.0106 \(\times\) 0.0005\(\lambda_{L}^{3}\) at the lowest operating frequency. The ferrite geometry consists of 44 plate-type ferrite cells (MP2106-0M0, Laird [21]) arranged into two stacked arrays--one with \(2\times 12\) grid cells on the bottom and one with \(2\times 10\) grid cells on the top--as shown in Figure 1a. The dimensions of each cell are \(L_{f}\times L_{f}\times H_{f}\). Figure 1b presents the feeding structure, which consists of two long microstrip lines at the center, ten short microstrip lines, and a coaxial probe. Two long microstrip lines \(L_{1}\times W_{2}\) in size are separated by a distance of \(d_{3}\). Each short microstrip line is \(W_{1}\times(L_{2}+L_{3})\) in size with one end connected to the long microstrip line and the other end connected to the ground plane. A pair of short microstrip lines on both sides forms a one-quarter rectangular loop, and there are five one-quarter rectangular loops in total wrapped around the ferrite. The feeding structure is designed using copper tape on Styrofoam; it has a relative dielectric constant of 1.03, a loss tangent of 0.0001, and a thickness of 3 mm. The Styrofoam is directly placed on top of the ferrite cells. A coaxial probe is used to feed the ferrite antenna, and the inner and outer conductors of the coaxial probe are connected to the upper and lower arms of the one-quarter rectangular loop located at the center. The design parameters of the proposed antenna are optimized to ensure high gain performance, and the optimized values are summarized in Table 1.  
The complex permeability and magnetic loss tangent properties of the MP2106-0M0 ferrite are shown in Figure 2. The complex permeability consists of a real part \(\mu^{\prime}\) and an imaginary part \(\mu^{\prime\prime}\). The magnetic loss tangent of the ferrite is calculated as \(\mu^{\prime\prime}/\mu^{\prime}\). The permittivity value of the ferrite is set to 12 in the operating frequency band (from 30 MHz to 300 MHz). As observed in Figure 2, the \(\mu^{\prime}\)-value of MP2106-0M0 is high in the low frequency band, and the magnetic loss tangent increases sharply as the frequency increases. For magnetic dipole applications, high radiation efficiency can be obtained with a high \(\mu^{\prime}\). Unlike a dielectric resonator antenna, the high magnetic loss tangent does not \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline \(L_{1}\) & 487 mm & \(W_{1}\) & 10 mm \\ \(L_{2}\) & 55 mm & \(W_{2}\) & 2 mm \\ \(L_{3}\) & 8 mm & \(d_{1}\) & 101.3 mm \\ \(L_{f}\) & 53 mm & \(d_{2}\) & 117.2 mm \\ \(H_{f}\) & 2.5 mm & \(d_{3}\) & 2 mm \\ \hline \end{tabular}
\end{table} 
Table 1: Optimized dimensional parameters of the proposed antenna. degrade the radiation efficiency of the magnetic resonator [19]. Therefore, the ferrite MP2106-0M0 is useful in the design of a magnetic dipole antenna operating on the VHF band. To determine how the magnetic field changes with different numbers of loop feeds, the magnetic field distribution around the ferrite dipole at 150 MHz is investigated, as shown in Figure 3, for the 1-loop feed, 3-loop feed, and 5-loop feed. With the 1-loop feed, the loop structure is located at the center of the ferrite dipole structure shown in Figure 3a. For the 3-loop and 5-loop feeds, there is one loop feed structure at the center, and two and four loop feeds are located on the both sides with intervals of \(d_{4}\) and \(d_{5}\), respectively. The values of \(d_{4}\) and \(d_{5}\) are 159 mm and 106 mm, respectively. In Figure 3b, a strong magnetic field forms around the loop feed structure and rarely extends to the  
Figure 1: Geometry of the proposed antenna: (**a**) 3-D view and (**b**) feeding structure.