# Quad-Band Circular Polarized Antenna for GNSS, 5G and WIFI-6E Applications
## 5 Measurement and Discussion  
The antenna is fabricated using etching technology on an FR4 substrate. The prototype is shown in Figure 9a. The 5-parameter is measured by an AV3672D vector network analyzer. The far field and gain are measured in a microwave anechoic chamber, as shown in Figure 9b. The axial ratio is retrieved from the radiation patterns.  
Figure 9: Fabrication and measurement: (**a**) front view of the proposed antenna; (**b**) back view of the proposed antenna; (**c**) far field measurement in an anechoic chamber.  
The simulated and measured S parameters, as well as AR, are plotted in Figure 10a,b, respectively. For reflection measurement, the antenna is placed in the anechoic chamber, and the cable is connected to the VNA. Before measurement, the cable is calibrated. As can be seen from the results, four frequency bands have been successfully realized. The \(-10\) dB bandwidths for the four bands are 75.8% (0.95-2.11 GHz), 55.8% (3.05-5.39 GHz), 39.9% (5.84-8.19 GHz), and 10.3% (9.14-10.68 GHz), respectively. The first band covers all four of the navigation systems (1.20 GHz-1.61 GHz). The second band covers several 5G bands. The third and fourth bands are for WIFI-6E and the satellite communication band.  
The measured 3 dB bandwidths for AR are 59.4% (1.16-2.14 GHz), 35.8% (3.23-4.64 GHz), 8.4% (5.70-6.20 GHz), and 2.6% (7.51-7.71 GHz). The measured gains are 4.56, 2.28, 4.26, and 4.30 dBi at 1.5 GHz, 3.8 GHz, 6 GHz, and 7.6 GHz, respectively. It can be observed that there is a good agreement between simulated and measured results. The slight difference is mainly due to the soldering error between the SMA connector and the feeder line. At the same time, when performing a far field test, the angle error between the turntables may also affect the test results. The measured results show that the proposed antenna can cover almost all navigation frequency bands, and it can cover 5G, N77, and N78 frequency bands at the same time.  
The measured and simulated far-field radiation patterns, in E-plane and H-plane, at 1.5 GHz, 4 GHz, 6 GHz, and 7.6 GHz are plotted in Figure 11. From the radiation patterns, it is clear that the antenna can radiate RHCP at 1.5 GHz, LHCP at 4 GHz, RHCP at 6 GHz, and LHCP at 7.6 GHz in the +z direction. It can also be seen that the antenna radiates a bidirectional wave with the opposite circular polarization. The RHCP is realized in the +z direction, while LHCP is in the -z direction.  
Figure 10: (**a**) The simulated and measured S11. (**b**) The simulated and measured AR.  
Figure 11: The simulated and measured gain patterns, in E plane and H plane, at (**a**) 1.5 GHz, (**b**) 4 GHz, (**c**) 6 GHz, and (**d**) 7.6 GHz.  
Gain measurement is conducted, by comparison, to standard-gain horn antenna. The measured gain versus the simulated gain is plotted in Figure 12. In the measurement, only the interested bands are measured. It can be seen that the measurement is in satisfactory agreement with the simulation. There are slight differences near 1.5 GHz and 6 GHz. However, the discrepancy is acceptable.  
A comparison between this work and the designs in the literature is presented in Table 2. Looking at the size of the antenna, this design is moderately large. In terms of operation bands, this work provides four working bands. Particularly, the first three bands have more than 39% relative bandwidths. The first bandwidth is even greater than 75%. Regarding the axial ratio bandwidth, the first band provides a bandwidth of 59.4%, making it the widest design in Table 2. In addition, this design covers all the four navigation systems. Moreover, extra bands can be applied for 5G and WIFI-6E applications. Therefore, this design provides more communication bands with larger bandwidth over an area of moderately large.