# A Miniaturized RHCP Slot Antenna for Wideband Applications Including Sub-6 GHz 5G
## 6 Measured Results
Accordingly, the gain values in Figure 18 accurately reflect the practical performance of the proposed antenna design. The simulation tools were used to estimate the radiation efficiency of the antenna, which varies from approximately 93% at 2 GHz to 85% at 4.7 GHz. This drop in efficiency is primarily due to the high loss tangent of the FR4 substrate, whose attenuation increases as the frequency increases. Despite this, the antenna maintains gain levels above 2 dBi throughout the band, confirming its suitability for real-world applications such as 5G sub-6 GHz systems, Wi-Fi 6E, and compact IoT devices, where the trade-offs between cost, size, and performance are critical. The simulated and measured co-polarized and cross-polarized radiation patterns of the proposed antenna are presented in Figure 19 at the YZ- and XZ-planes at the three resonant frequencies. The evidence of the presence of CP in the broadside direction (\(\theta~{}=~{}0^{\circ}\)) is that the co- and cross-polarization radiation patterns are close to each other with a difference of less than 3 dB between them for both planes at this direction of propagation. Briefly put, this design is a wide-slot antenna that has a wide impedance BW and a wide ARBW in spite of its small dimensions. In addition, the gain value is accepted along the impedance BW. Furthermore, the radiation pattern is stable along the operational band. However, the disadvantage of the wide-slot antenna lies in the complicated steps that are followed to accommodate the shape of the slot with the shape of the tuning stub to achieve reasonable line-slot coupling. The effective noise temperature of the antenna as a function of the frequency should also be highlighted in this work to demonstrate the effect of the galactic noise and the atmospheric noise on the antenna performance. In fact, several references provide empirical data and equations about the effective noise temperature and its variation with respect to  
Figure 18: Simulated and measured realized gain of the proposed antenna as a function of the frequency. the galactic noise and atmospheric noise, which includes the humidity and water vapor effects. However, reference [53] has specifically discussed the effective noise temperature of the antenna as a function of the frequency. It is shown that the galactic noise effect decreases gradually as the frequency increases until it reaches its minimum values at frequencies above 1 GHz. In contrast, the atmospheric noise (including the humidity and water vapor) effect increases as the frequency increases, but its effect is subtle at frequencies below 10 GHz. As a result, the effective noise temperature of the antenna is minimal within the range (1-10 GHz). It is important to note that the proposed design has a bandwidth within the given range, so the atmospheric and galactic noise has a negligible effect on its performance. As summarized in Table 1, the proposed antenna exhibits competitive performance when compared to state-of-the-art wide-slot CP antennas. Notably, it achieves a wide 3 dB axial ratio bandwidth (2.08-4.37 GHz), a high peak gain of 4.68 dB, and excellent radiation efficiency of 93% at the first resonant frequency, while maintaining a compact size (0.39\(\lambda\)\(\times\) 0.36\(\lambda\)\(\times\) 0.011\(\lambda\) at 2.2 GHz) with the aid of a low-cost FR4 substrate. Com  
Figure 19: Simulated and measured results of the normalized co- and cross-polarization power patterns of the proposed antenna at (**a**) f = 2.2 GHz, (**b**) f = 3.1 GHz, and (**c**) f = 4.2 GHz. pared to designs based on high-performance substrates such as Rogers 5880 or 4350B, the proposed design demonstrates superior or comparable performance using a more economical material. Additionally, unlike several references that focus on narrowband or single-band operation, this antenna supports broadband circular polarization suitable for multi-standard applications such as sub-6 GHz 5G, WiMAX, and Wi-Fi.