# The Uses of a Dual-Band Corrugated Circularly Polarized Horn Antenna for 5G Systems
## 3 Corrugated Antenna Design  
A corrugated structure has been a part of the horn antenna's application for many decades. When the horn antenna radiates on the open end of the horn structure, the electromagnetic wave will creep on the metal surface to become surface wave. This will increase the side lobe of the far field pattern and decrease the antenna gain. Then, the corrugated structure will mitigate this phenomenon. [PERSON] [14] also defined the soft surface to describe the physics of surface wave on metal surfaces, as illustrated in Figure 5a. It pointed out that surface wave cannot propagate on soft surfaces by using a quarter wavelength depth of the corrugated structure. Furthermore, it stated that the resistance of wave incident direction is infinite and that the impedance of orthogonal direction on wave propagation is zero. This will cause the horn antenna to have a lower side lobe and a higher antenna gain. On the other hand, surface wave application has also been implemented to design a leaky-wave antenna, as shown in Figure 5b. Leaky wave is a characteristic of surface wave, and it can be observed as a signal source when propagating high dielectric substrate. It scatters far-field wave by using a periodic metal structure [15]. In Figure 6, a non-quarter wavelength of corrugated structure is applied to radiate far field by using the leaky-wave antenna theory. This, in effect, will contribute towards a broad beam width effect on the far field pattern of the horn antenna. Table 2 lists the optimized parameters of the corrugated horn antenna. Here, we use two different gap sizes W1 and W2 to control the low and high band beam width. In Figure 7, the configuration of the antenna showed the combination of a circularly polarized converter and a corrugated structure. The simulated input return loss is shown in Figure 8. Results show that \(\mid\)S11 \(\mid<-18\) dB at 26.5 GHz to 30 GHz, and 36.5 GHz to 40 GHz. This antenna bandwidth meets the specifications of bands n257 and n260. In Figure 9, the simulated axial ratio result shows that AR \(<\) 5.5 dB for low band and AR \(<\) 4 dB for high band. Figures 10 and 11 show the total gain pattern and circularly polarization gain pattern of two cut planes on low band and high band, respectively. The corrugated horn antenna and the pure horn antenna are shown in Figure 12. The simulation results show that the corrugated structure improved the beam width of the horn antenna, as shown in Figures 13 and 14. In low band, the beam width was increased from 48 degrees to 96 degrees; about a 100% improvement. While in high band, the beam width was increased from 52 degrees to 68 degrees; about a 30% improvement. Figure 5: (a) Definition of soft surface and (b) leaky-wave antenna. Figure 6: (a) Corrugated horn antenna, (b) parameter of cross section of detail corrugated antenna. R1 is the radius of the corrugated horn. W1 and W2 is the gap width of the corrugated horn, and H1 is the depth of the corrugated horn. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values (mm)** \\ \hline R1 & 10 \\ \hline R2 & 4.2 \\ \hline H1 & 1 \\ \hline H2 & 5 \\ \hline L1 & 0.6 \\ \hline L2 & 0.5 \\ \hline W1 & 1 \\ \hline W2 & 0.63 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters of the corrugated structure. Figure 7: 3D simulation coordinate of corrugated horn antenna. Figure 8: Return loss of simulation result. Figure 10: _Cont_. Figure 9: Axial ratio of simulation result. Figure 11: (**a**) Total gain pattern of simulation result on high band for XZ-Cut, (**b**) total gain pattern of simulation results on high band for YZ-Cut, (**c**) co-pol (RHCP) and cross-pol (LHCP) gain pattern on 37 GHz for XZ-Cut, and (**d**) co-pol (RHCP) and cross-pol (LHCP) gain pattern on 37 GHz for YZ-Cut.