# Inverted F Type Antenna Design for the Cattle Activity and
## 3 Simulation and Measurement  
The antenna simulation model with CST is shown in Figure 5. According to all the limitations related to the size, height, and location of the module and notch of the cover, the lengths of all the parameters of the antenna for simulation are shown: 20 \(<\) L1 \(<\) 25 mm, L2 \(<\) 30 mm, 3 \(<\) h \(<\) 5.5 mm, w = 3 mm, the gap between feeding and the ground is about 2-4.4 mm on the FR4 board. The width of antenna w is not as sensitive as the other parameters. The optimization of each parameter value to match the antenna to the frequency of the ZigBee 2.45 GHz, and the parameters are adjusted within the limitations of all parameters. The simulated and optimized parameters of the antenna are L1 = 20, L2 = 5, height h = 5.5 mm, and gap = 4 mm. The simulated results of the antenna are shown in Figure 6 with the variation of length of L2. The results of the return loss of the antenna when the length of L1 = 20 mm and length of L2 vary from 5 to 8 mm. As the length of L2 increases, the resonant frequency of the antenna shifts to the lower frequency, as expected. The optimum of L2 is 5 mm when L1 = 20 mm and h = 5.5 mm. The optimized total length of the proposed IFA antenna L1 + L2 + h is about 31.5 mm, which is close to the theoretical length of the IFA antenna of about 31 mm, which is \(\lambda/4\) of the ZigBee frequency of 2.45 GHz. The simulation result \(\mid\)S11\(\mid\) of the proposed antenna is shown in Figure 7 with the given parameters, as the length of L1 + L2 + h = 31.5 mm. The S11 of the proposed antenna is \(-\)17 dB at 2.45 GHz. The measurement results of S11 with the cover and without the cover of the cases are shown in Figure 8. Since the antenna has been designed with the cover shown in Figure 4, the measurement result with the cover is better than the result without the cover of the module. It shows that the S11 is \(-\)19.45 dB with the cover and \(-\)14.4 dB without the cover, as shown in Figure 8.  
Figure 6: Variation of S11 due to the length of L2. The simulated antenna radiation 3D patterns with antenna design coordinates are shown in Figure 9a, and radiation patterns of x-z and x-z planes are shown in Figure 9b,c with the antenna structure. The antenna is designed on the x-y plane, and Figure 9a shows the 3D antenna radiation pattern matched to antenna coordinates. The maximum gain is 1.6 dBi in the z-axis \(-17\) degrees direction, as shown in Figure 9a. The reason the antenna pattern is tilted is that the ground plane does not exist in the Y direction of the antenna, so it is tilted about \(-17\) degrees toward the ground. In Figure 9c, the gain at 180 degrees is about 1.5 dBi, and the gain at 0 degrees is about 1.3 dBi. The reason why the gain of the 180 degrees part shows a greater gain than the 0 degree part is that the vertical component L2 part of the antenna is present at 180 degrees, which leads to more radiation and gain. The antenna was installed in the case to check the performance change, as shown in Figure 8, according to the presence or absence of the case cover. The fabricated prototype of the IFA antenna shown in Figure 10a was built on a 30-millimeter thick RF IS-680 board with relative dielectric constant equals to 3.2. The SMA connector has been used for the measurement of S11. The length of L2 was shortened from 30 to 0 mm, while S11 has been measured as shown in Figure 8. The best results around \(-19\) dB at 2.45 GHz have been obtained when L2 was 5 mm. Figure 8: Measured return loss of the fabricated IFA antenna of the sensor module (**a**) with the cover of the module and (**b**) without the cover of the module. Figure 7: Scheme \(11\) of the proposed IFA antenna of the sensor module. After verifying the antenna performance of the designed IFA antenna with an Agilent PNA network analyzer, the IFA antenna has been built on the RF module as shown in Figures 2 and 4, and the RF module with the IFA antenna is installed on the mainboard shown in Figure 10b.