# Low-Profile Dual-Polarized Antenna Integrated with Horn and Vivaldi Antenna in Millimeter-Wave Band
## 4 Results and Discussions  
The antenna has the dimensions of 39.7 mm \(\times\) 18 mm \(\times\) 3.3 mm. To verify the performance of the proposed antenna, a prototype is fabricated and measured. The \(S-\)parameters of the dual\(-\)polarized antenna are tested by an Agilent vector network analyzer E8363B, and the radiation pattern is measured in an anechoic chamber. Due to the test equipment limitations, the pattern is only tested from \(-90^{\circ}\) to \(90^{\circ}\). Figure 11 shows the fabricated prototype of the dual\(-\)polarized antenna. The simulated and measured results of \(S-\)parameters are shown in Figure 12. The simulated reflection coefficients of both polarizations are lower than \(-10\) dB in the range of 20.25-26.55 GHz (26.92%), while the measured ones are 20.04-25.5 GHz (23.98). The simulated and measured results have a reasonable agreement.  
Figure 11: Fabricated prototype of the proposed dual\(-\)polarized antenna.  
Figure 10: Reflection coefficient of the horn antenna with respect to different \(W_{6}\).  
The measured isolation between the two ports of the antenna is above 36 dB in the operating band, indicating that the antenna has good isolation between the two polarizations. When port 1 of the Vivaldi antenna is excited, the antenna exhibits good directionality at 22.5 GHz, as shown in Figure 13. The peak simulated gain of the Vivaldi antenna is 8.2 dBi at 22.5 GHz, while the measured gain is 7.0 dBi. Both simulated and measured cross\(-\)polarizations are lower than \(-\)20 dB. The maximum radiation direction deviates slightly from the normal direction due to the asymmetry of the antenna. When port 2 of the horn antenna is excited, the radiation pattern of the antenna is shown in Figure 14. It is shown that the horn antenna has the simulated gain of 7.1 dBi and the measured gain of 5.2 dBi. The simulated and measured cross\(-\)polarization are both lower than \(-\)26 dB. As shown in Figure 15, the horn antenna also achieves the maximum gain at 22.5 GHz. The dual\(-\)polarized antenna has a stable gain in the 20-23.5 GHz range for both polarizations. The difference between simulation results and measurement results may be from the air gap between the two dielectric substrates. Since the antenna is combined with two substrate layers and connected by screws, the air gap will inevitably appear. In addition, since the air gap between the two dielectric substrates is not the same everywhere, this difference is also difficult to verify by simulation results.  
Figure 14: Simulated and measured radiation pattern at 22.5 GHz when port 2 is excited. (**a**) \(xOz\) plane for HP, (**b**) \(yOz\) plane for HP.  
Figure 13: Simulated and measured radiation pattern at 22.5 GHz when port 1 is excited. (**a**) \(xOz\) plane for VP, (**b**) \(yOz\) plane for VP.  
To illustrate the advantages of the proposed dual\(-\)polarized antenna in detail, the performance of some existing dual\(-\)polarized antenna element and antenna array compared with the proposed design is listed in Table 2. With the exception of ref. [27], the proposed antenna has a wider overlapped impedance bandwidth than other contrasting antennas. This is thanks to the way one obtains dual polarization, i.e., by integrating two wideband antennas: the horn antenna and the Vivaldi antenna. It is also obvious that the antenna has great isolation between two polarizations. The high isolation of the antenna comes from the use of different feed structures at the two ports. However, some antenna arrays are listed in Table 2, which makes the comparison of gain unclear. The high gain of the proposed antenna can be seen from the comparison with ref. [20] and ref. [27,28]. The antenna owns high gain since it adopts a dielectric lens to enhance directivity. Additionally, the antenna is designed using SIW technology, which has the advantage of being easy to integrate and having a low profile. Therefore, the proposed antenna is a wideband antenna with high gain and good isolation.