## 5 Results and Discussion  
### Reflection Coefficients and Radiation Patterns in Free Space  
The proposed antenna was fabricated, as shown in Figure 10a. The antenna reflection coefficient \(|\)S\({}_{11}\) \(|\) was measured using the Keysight vector network analyzer, which ranges from 300 KHz to 44 GHz. The connectors used also supported RF signal feeding up to 50 GHz. The \(|\)S\({}_{11}\) \(|\) measurement setup is shown in Figure 10b. The CMA results indicate that Mode 1 and 2 are resonant, with Mode 3 partially contributing to the resonance at 25.5 GHz with a bandwidth of 24-27 GHz. At 38 GHz, Mode 1-3 are resonant with a bandwidth of 26.2-39.3 GHz. The high-frequency simulation software (HFSS) version 21.0 results illustrate the occurrence of two resonances at 25.5 and 38 GHz with a bandwidth of 750 MHz (25-25.75 GHz) and 1 GHz (37.92-38.92 GHz). The measured \(|\)S\(111\) \(|\) shows resonance at 25.85 and 38 GHz with bandwidths of 1.5 GHz (25-26.5 GHz) and 2.5 GHz (37-39.5 GHz), as displayed in Figure 11a. The deviation in the measured results may be due to fabrication tolerance, cable, and connector losses. The procured connectors (the best available in the market) also have a 1.2 mm gap between the center signal and ground lead. When the antenna is fitted inside, a gap of 0.94 mm still exists that is filled with excessive soldering lead, as shown in Figure 12. Above all, the proposed antenna is very small and lacks industrial standard soldering tools, necessitating manual soldering that causes a lead spread on the ground plane. All of this impacts the antenna's performance, causing deviations in the measurement results, as shown in Figure 11. However, the measured results are considerable compared to the simulated results. The antenna has an almost constant simulated and measured gain of 7.4 and 7.9 dBi at first resonance. Nonetheless, at second resonance, the gain almost linearly increases with the maximum simulated and measured gains of 7.4 and 7.3 dBi, as shown in Figure 11b.  
Figure 8: Variation in (a) reflection coefficient \(|\)S\(111\) \(|\) due to a change in the variable BEL, (b) Real and (c) imaginary impedance values at respective BEL values.  
Figure 9: Effect of varying TEL on (a) the reflection coefficient \(|\)S\({}_{11}\), (b) the real part of the impedance, and (c) the imaginary parts of impedance.  
As discussed in the current distribution section, the proposed antenna generates TM\({}_{10}\) and TM\({}_{02}\) at 25.5 and 38 GHz, respectively. Due to these modes, the radiation is a single beam in the broadside direction at 25.5 GHz, whereas two beams at 38 GHz are tilted at 36\({}^{\circ}\). Therefore, the radiation pattern is measured on the XZ- and YZ-planes at 25.5 GHz (Figure 13a,b), whereas, at 38 GHz, only the YZ-plane is considered (Figure 13c). The simulated and measured half-power-beamwidths (HPBWs) at 25.5 GHz are 78\({}^{\circ}\) and 62\({}^{\circ}\) on the XZ-plane. On the YZ-plane, they are 82\({}^{\circ}\) and 62\({}^{\circ}\). At 38 GHz, the simulated and measured HPBWs are 58\({}^{\circ}\) and 45\({}^{\circ}\).  
Figure 11: Simulated and measured reflection coefficients and gain. (**a**) \(\mid\)S\({}_{11}\mid\) and (**b**) gain.  
Figure 12: 3D representation of the proposed antenna with the SMA connector.