# A Small Implantable Compact Antenna for Wireless Telemetry Applied to Wireless Body Area Networks
## 3 Antenna Design and Simulation  
### Antenna Structural Design  
The antenna was designed on a Rogers RT 5880 (Rogers Corporation, Chandler, AZ, USA) (\(\varepsilon_{r}\) = 2.2, loss angle tangent = 0.0009) substrate with a thickness of 0.13 mm. In order to avoid direct contact between the radiating patch of the antenna and the human body, which in turn affects the performance of the antenna, we also added a layer of 0.4 mm thick silicone on top of the antenna to be used as a cover layer. The antenna presented herein is a compact microstrip patch antenna with a zigzag structure, making it highly suitable for implantable devices and an ideal choice for implantable antennas in Wireless Body Area Networks (WBANs). The radiating patch, which incorporates zigzag slots and various rectangular slots, achieves compactification and bandwidth enhancement of the antenna. The rectangular slots on the ground plane improve impedance matching, as shown in Figure 3. The detailed parameters of the antenna are outlined in Table 2. A coaxial feeding point with a diameter of 0.3 m is located at the bottom left corner of the antenna patch at position P (x = \(-\)2.2 mm, \(y\) = \(-\)2.2 mm), as indicated by the white circle in the Figure 3.  
Figure 3: Structural diagram of the proposed antenna.  
Figure 2: Measurement device.  
The design process of the antenna is depicted in Figure 4. Slots are introduced on the radiating patch, and zigzag structures are added to achieve compactification while maintaining broadband characteristics. Each step in the design process corresponds to a specific reflection coefficient.  
Initially, F-shaped and S-shaped zigzag slots are introduced on the rectangular radiating patch to extend the antenna's current path and induce resonance. As shown in Figure 5, the antenna resonates at 2.73 GHz, but the resonant frequency is too high, and the operating bandwidth does not cover the ISM band. In step 3, an additional rectangular slot is introduced on the radiating patch, reducing the antenna's resonant frequency and achieving compactification. However, the bandwidth is narrow, and the reflection coefficient is poor. In step 4, a rectangular ground plane is used to expand the antenna's bandwidth. The antenna's operating frequency band is 2.08-2.64 GHz, fully covering the required frequency band. From the before mentioned design steps, it is evident that the introduction of zigzag-shaped rectangular slots on the radiating patch achieves antenna compactification. Further, by adding open rectangular slots on the radiating patch and ground plane, the antenna gains good impedance matching and operating bandwidth, resulting in a compact broadband implantable antenna.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Parameter** & **Size (mm)** & **Parameter** & **Size (mm)** & **Parameter** & **Size (mm)** \\ \hline W & 6 & s\({}_{1}\) & 4.4 & s\({}_{7}\) & 0.2 \\ L & 6 & s\({}_{2}\) & 0.4 & s\({}_{8}\) & 0.3 \\ G & 4.5 & s\({}_{3}\) & 2 & s\({}_{9}\) & 2.8 \\ l\({}_{1}\) & 0.3 & s\({}_{4}\) & 1.5 & s\({}_{10}\) & 2 \\ h & 0.13 & s\({}_{5}\) & 0.5 & s\({}_{11}\) & 3 \\ h\({}_{1}\) & 0.4 & s\({}_{6}\) & 3 & r & 0.3 \\ \hline \end{tabular}
\end{table}
Table 2: Parameters of the proposed antenna.  
Figure 4: Design process of the proposed antenna.