# A Four-Port Dual-Band Dual-Polarized Antenna for Ku-Band Satellite Communications
## 3 Experimental Results and Discussion  
Based on the optimized design parameters, the proposed four-port shared-aperture DBDP antenna is fabricated with six Taconic TLE-95 substrate layers of different thicknesses. These substrate layers are bonded together using Roger RO4450T bonding sheets with the same thickness of 0.0762 mm. Figure 7a shows a photograph of the fabricated antenna. The antenna is 14.55 mm \(\times\) 14.55 mm \(\times\) 3.61 mm in size. Each excitation port of the antenna is connected with a semi-flexible pigtail cable (part number: SR047-KF1). The \(S\)-parameters were tested using the ShockLine(tm) MS46122B vector network analyzer from Anritsu. The far-field radiation characteristics of the fabricated antenna were measured in an RF anechoic  
Figure 5: Simulated \(|S_{33}|\) for each step of the design procedure for the HB antenna. Figure 6: Effect of the shorting pin on the (**a**) \(|S_{33}|\) and (**b**) \(|S_{43}|\) of the HB antenna. (**c**) Simulated current distribution of the HB antenna with and without the shorting pin when **P3** excited. chamber, as shown in Figure 7b. A dual-polarized rectangular horn antenna was utilized to attain the co-polarized/cross-polarized waves. Figure 8a-c illustrate a comparison of the simulated and measured \(S\)-parameters of the proposed antenna. The simulation and measurement are found to be in reasonable agreement. The measured results are slightly shifted down approximately 300 MHz in comparison with the simulated results. Multilayer PCB manufacturing uncertainties are primarily responsible for this discrepancy. Referring to Figure 8a, the measured \(-\)10 dB IBW of 9.28-12.96 GHz (33.10%) is achieved for both **P1** and **P2** of the LB antenna, covering the entire Rx band of 10.7-12.75 GHz. Within the \(-\)10 dB IBW, the measured isolation between two orthogonal polarizations (\(|S_{21}|\)) of the LB antenna is larger than 12 dB. Referring to Figure 8b, the measured \(-\)10 dB IBWs of the LB antenna are 13.21-15.88 GHz for **P3** and 13.10-15.32 GHz for **P4**. Although the antenna is symmetrical, there is a discrepancy in the measured results of \(|S_{33}|\) and \(|S_{44}|\), which is mainly caused by imperfections in the hand soldering process. An overlapped IBW of 13.21-15.32 GHz (14.79%) is achieved for the HB antenna, covering the whole Tx band of 13.75-14.5 GHz. Within the overlapped IBW, the measured isolation between two orthogonal polarizations (\(|S_{43}|\)) of the HB antenna is larger than 12.4 dB. The Tx/Rx isolations, namely \(|S_{31}|\) and \(|S_{41}|\), are depicted in Figure 8c. As observed, the measured Tx/Rx isolation of more than 14 dB is achieved in both the Rx band and Tx band. Figure 7: Photograph of the (**a**) fabricated antenna and (**b**) far-field measurement environment. The simulated and measured realized gains of the proposed antenna are depicted in Figure 9a,b. Within the Rx band, the measured realized gain ranges from 4.18 to 6.02 dBi for **P1** and from 4.62 to 6.63 dBi for **P2**. Meanwhile, the measured realized gains of 4.99 to 5.42 dBi and 4.65 to 5.23 dBi are achieved for **P3** and **P4**, respectively, within the Tx band. The measured and simulated radiation patterns of the proposed antenna in the \(xz\)-plane (\(\phi\) = 0\({}^{\circ}\)) and yz-plane (\(\phi\) = 90\({}^{\circ}\)) at 11.75 GHz (for Rx band) and 14 GHz (for Tx band) are plotted in Figure 10a-d. The measured cross-polarization in the boresight direction remains \(\geq\)20.1 dB and \(\geq\)18.4 dB in the Rx band and Tx band, respectively. It is also seen from Figure 10 that the off-axis cross-polarization in the E-plane is high, especially at 14 GHz (Tx band). Sequential rotated feeding can be applied to overcome this problem when designing a Tx/Rx dual-polarized phased-array antenna based on the proposed design. We compare the proposed antenna with previously reported DBDP antennas in Table 1. Compared to previous antennas [13; 15; 16], the proposed antenna has a smaller frequency ratio and a smaller size.