## 4 Results and Discussion  
The circular Minkowski fractal antenna with a partial ground plane was constructed using a fire-retardant (FR-4) substrate, which was then measured to confirm its UWB performance. The reflection coefficient (S11) in decibels (dB) and voltage standing wave ratio (VSWR) were measured using the VNA with a frequency range of 9 KHz to 13.6 GHz; connectors were employed for connecting the designed antenna to the VNA. Figures 8 and 9 show the captured S11 and VSWR results, respectively, from the VNA. The top view and bottom view of the CMFA prototype are shown in Figure 10a and Figure 10b, respectively. Furthermore, the proposed antenna radiation pattern is examined within an anechoic chamber, with a horn antenna serving as the receiver and the proposed antenna as a transmitter, as illustrated in Figure 10c. The radiation characteristics measurement in the anechoic chamber is shown in Figure 10c,d. The experimental setup for measuring the reflection coefficient is shown in Figure 10e. Figure 8: Reflection coefficient of the circular Minkowski fractal antenna. Figure 7: Simulated reflection coefficient curve for different indentation ratios of the fractal antenna. The CMFA's simulated impedance bandwidth spans from 3.17 GHz to 12.45 GHz, boasting a 118.7% impedance bandwidth. Notably, it achieves a minimum reflection coefficient of \(-\)34.71 dB at 9.7 GHz and \(-\)34.15 dB at 4.06 GHz. The measured impedance bandwidth of the antenna is observed between 3.37 GHz and 13.6 GHz (with S11 \(<-\)10 dB); this presents an impressive 120.6% impedance bandwidth with a minimum reflection coefficient of \(-\)40.03 dB. The antenna exhibits three resonant frequencies: 4.43 GHz, 6.07 GHz, and 9.3 GHz, rendering it well-suited for multi-functional wireless applications across the S, C, and X bands. The incorporation of the Minkowski fractal pattern on the antenna leads to enhancements in bandwidth, impedance matching, and gain. Remarkably, a strong correlation is evident between the measured and simulated results. Figure 8 depicts the measured and simulated reflection coefficients of the proposed antenna. The measured S11 closely aligns with the simulated counterpart across the majority of the intended frequency spectrum. The measurements validate the anticipated UWB traits as predicted in the simulation, albeit with a minor deviation observed at the lower edge frequency. Furthermore, the measurements substantiate the pass-band characteristics, as demonstrated in Figure 8. Discrepancies between the measured and simulated outcomes are largely attributed to fabrication and soldering tolerances of the SMA connector, which are aspects that the simulation fails to account for. Additionally, the simulation maintains a constant dielectric loss tangent for the FR-4 substrate, while in reality, this tangent varies with frequency. Figure 9 illustrates the VSWR for the circular Minkowski fractal antenna. The circular Minkowski fractal antenna demonstrates a VSWR of less than 2 across the frequency range of 3.37 GHz to 13.6 GHz, which is a validation conducted through VNA testing. The antenna's gain is determined utilizing the comparative gain measurement technique within a 5 m \(\times\) 3 m \(\times\) 3 m anechoic chamber and is calculated using the following equations [16,21]:  
\[\frac{P_{SG}}{P_{t}} =\left(\frac{\lambda}{4\pi R}\right)^{2}G_{t}G_{SG} \tag{11}\] \[\frac{P_{AUT}}{P_{t}} =\left(\frac{\lambda}{4\pi R}\right)^{2}G_{t}G_{AUT} \tag{12}\]  
where \(R\) is the distance between the transmitting and receiving antennas, \(P_{SG}\) is the power of the standard gain antenna, \(G_{SG}\) is the gain of the standard gain antenna, \(P_{AUT}\) is the power of the antenna under test, \(G_{AUT}\) is the gain of the antenna under test, \(P_{t}\) is the power  
Figure 9: VSWR of the circular Minkowski fractal antenna. of transmitting antenna, \(G_{t}\) is the gain of transmitting antenna, and \(\lambda\) is the operating wavelength.