## 2 Antenna Design
### Design Methodology  
As above-mentioned, the application demands an internal antenna. To avoid the integration phase and the risk of facing difficulties in adjusting the resonant frequencies to the target ones, designing an antenna with the presence of all the device parts is, without a doubt, the best solution. Figure 1b shows the 3D model of the device with the designed antenna inside the enclosure. Figure 1a shows an exploded view of the device. The used enclosure material is the polyamide. The battery holder material is prototyped using photopolymer resin [33]. The manufacturers of these two materials do not provide any information about their dielectric constants or dissipation factors. In [34], the polyamide has a value between 3.34 and 6, and an average of 4.54, these values are not referred to a specific frequency. Moreover, its dissipation factor has a value between 0.005 and 0.182, and an average value of 0.04.  
In [35], the photopolymer resin was characterized and its dissipation factor and dielectric constant at 63 MHz were 4.11 \(\pm\) 0.06/0.025 \(\pm\) 0.002. For the polyamide, in simulation, we took 3 and 0.04 as initial values of the dielectric constant and the dissipation factor, respectively. For the photopolymer resin, the dielectric constant and dissipation factor are set to \(\epsilon_{\mathrm{r}}\) = 4.1 and tan \(\delta\) = 0.025. The antenna is realized using a low-cost, FR-4 material with a thickness of t = 1.6 mm, \(\epsilon_{\mathrm{r}}\) = 4.7, tan \(\delta\) = 0.016 and a copper thickness of 35 \(\upmu\)m.  
The proposed reconfigurable antenna shown in Figure 2 consists of a meaneded line structure [27; 29; 30; 31; 32; 33] with a capacitive short loaded with lumped components [33], an asymmetrical ground plane [36], a stub-like conductor, and a PIN diode to realize the frequency configurability [23; 24]. The values of the geometric parameters of the antenna structure are shown in Table 1. The antenna resonates at 466 MHz in the ON states and resonates at 401 MHz and 868 MHz in the OFF state. The geometric parameters of the antenna structure are set, so that the antenna resonates a little bit higher than 466 MHz. The loaded lumped components on the radiating structure are used to adjust the resonant frequency to 466 and 401 MHz, but also to compensate the frequency shift due to the enclosure. The stub-like is used to control the higher resonant frequency, 868 MHz. The capacitive short is used to control the impedance matching of the antenna. Parametric studies on the values of lumped components and the equivalent model of the PIN diode are performed to understand the response of the input reflection coefficient of the antenna. The antenna is designed with the enclosure and all the parts of the device using, and simulations, are performed using HFSS.  
Figure 1: Designed tracker: (**a**) exploded view of the tracker device; (**b**) assembled parts of the tracker device.  
Figure 2: Proposed antenna: (**a**) top view: structure reserved for GPS and BLE (black color); (**b**) lumped components, UFL connector and PIN diode placements; (**c**) bottom view; (**d**) top view with geometric key parameters.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value (mm)** & **Parameter** & **Value (mm)** \\ \hline L & 88 & l\({}_{2}\) & 23 \\ W & 78 & l\({}_{3}\) & 18.55 \\ C & 8 & l\({}_{4}\) & 16.3 \\ c\({}_{1}\) & 8.6 & l\({}_{5}\) & 4.4 \\ G & 2 & l\({}_{6}\) & 47.3 \\ g\({}_{1}\) & 0.65 & W & 2 \\ g\({}_{2}\) & 3 & w\({}_{1}\) & 1.85 \\ L & 12.5 & w\({}_{2}\) & 3.3 \\ l\({}_{1}\) & 14.3 & w\({}_{3}\) & 0.61 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Key geometric parameters of the antenna.