# Ferrite-Loaded Spidron Fractal Loop VHF Antenna for UAV Applications
## 3 Experimental Verification  
Figure 6a presents a photograph of the proposed antenna. To simplify the fabrication and measurement steps, the size of the ground plane is reduced. The ground plane of the fabricated proposed antenna has a square structure with a length of 0.3 m. Figure 6b shows a top view of the fabricated ferrite structure. The configuration for the optimized ferrite has it is attached onto the center of the ground plane. Six nylon posts with a relative dielectric constant of 3.2 are used to support the substrate with an etched Spidron fractal structure. The antenna measurement circumstance is illustrated in Figure 6c. The gain was measured in an electromagnetic wave open area test site 60 m \(\times\) 30 m in size at the Korea Research Institute of Standards and Science. The transmission and receiving antenna (proposed antenna) is positioned 6 m above the ground. Figure 7 presents the simulated and measured realized peak gains of the proposed antenna on the \(xz\)-plane. The realized peak gains are the total radiated power of the linear polarization. The simulated and measured gains range from \(-\)35.8 to \(-\)5.1 dBi and from \(-\)31.6 to \(-\)1.9 dBi, respectively. This graph indicates that the simulated and measured results are in good agreement in the operating frequency band. The slight difference between the simulated and measured results arose due to calibration differences and reflected and scattered waves from the ground. Figure 5: Simulated realized peak gains and efficiency rates of the Spidron fractal loop antenna with optimized and cuboid ferrite. Simulated and measured radiation patterns at 60, 180, 300 MHz on two planes (\(xz\)-plane and \(yz\)-plane) are shown in Figure 8. The simulated and measured results are indicated by the dashed and solid lines, respectively. The radiation patterns of the proposed antenna are omni-directional at all frequencies. The feeding location is tilted toward the \(+x\)-axis relative to the center of the antenna, resulting in some asymmetry patterns. The differences between the simulated and measured results arose due to the weather at the measurement center, manufacturing uncertainties, and similar causes. Figure 6: (**a**) 3-D view of the fabricated proposed antenna; (**b**) Top view of the optimized ferrite structure; (**c**) Antenna measurement circumstances. Figure 7: Simulated and measured realized peak gains of the proposed antenna on the \(xz\)-plane. Figure 9a,b show a 3-D view and bottom view of the UAV model, respectively. The shape of the UAV is modeled to examine the performance of the proposed antenna mounted on the UAV. The UAV model consists of a fuselage and wings, and all surfaces are implemented as conductors. The size of the UAV model is similar to the size of a typical UAV. The proposed antenna is mounted on the bottom of the fuselage of the UAV and faces the--\(z\)-axis. Figure 10 presents the simulated realized peak gains of the proposed antenna on a UAV and on flat ground. Flat ground here is defined as the proposed antenna on a square ground plane with the area denoted by round brackets. On flat ground, the simulated gains for the (0.3 m \(\times\) 0.3 m) case are approximately 5 dBi lower than that for the (10 m \(\times\) 10 m) case in the operating frequency band owing to the ground size. By mounting the proposed antenna on the UAV, the overall structure of the UAV becomes the ground of the antenna. The gain characteristics on the UAV are similar to those on flat ground (10 m \(\times\) 10 m) because the ground size of the antenna on the UAV is sufficiently large. Therefore, flat ground (10 m \(\times\) 10 m) can be used instead of a UAV model. The realized gains of the proposed antenna on UAV range from \(-\)23.9 to \(-\)0.6 dBi. The slight discrepancies in the gain of the antenna on the UAV and flat ground (10 m \(\times\) 10 m) are caused by the antenna directivity, which is affected by the UAV structure.