## 4 The 32 \(\times\) 24 Phased Array  
In this paper, a 32 \(\times\) 24 antenna array is fabricated to validate the beam-scanning characteristic, whose configurations are presented in Figure 16. The 32 \(\times\) 24 phased array is equivalent to doubling the 16 \(\times\) 24 array in the \(x\)-direction. During the measurement process, each of the eight Rx ports is connected with low noise amplifiers (LNAs); then, eight coaxial cables for connecting the LNAs and the phase-shifting module are adopted. The Tx band ports are connected with eight phase-shifting channels separately, and the power amplifier (PA) is placed in front of the power divider for convenience. The beam-scanning normalized radiation patterns in the Rx and Tx bands are presented in Figure 17,b. Due to the limited scanning angle requirements, the scanning range designed here is relatively small. The measurements show that the radiation pattern can be steered over the elevation range from \(-5^{\circ}\) to \(5^{\circ}\). The measured radiation patterns are in good agreement with the simulated ones. As shown in Figure 18a,b, the measured bandwidths of all the Rx and Tx ports are 26.1 % (from 10.85 GHz to 14.1 GHz) and 11 % (from 13.3 GHz to 14.85 GHz), respectively. The ports working in the Tx-band are greatly affected by the SMA welding; therefore, the S-parameters of these ports are inconsistent. Figure 18c shows that the isolations in the Rx band and Tx band are greater than 36.7 dB and 40 dB, respectively. In addition, the realized gains of the 32 \(\times\) 24 antenna array are shown in Figure 18d with the elimination of the transmission losses of the coaxial line and connectors. Due to the limitation of the simulation environment, only the simulation results at the central frequencies (i.e., 14.25 GHz and 12.5 GHz) are available. The gain results are above 29.7 dBi across the Tx and Rx bands. The discrepancy between the simulated and measured gains is due to the interference of the surface metal coating technology on the microstrip feed line, which has been discussed in Section 3. The characteristics of low pointing error, wide bandwidth, and high isolation are particularly valuable for SATCOM beam-scanning applications. Figure 15: Analysis of the MS structure with and without the ENIG technology: (**a**) Simulated and measured S-parameters of the microstrip line with different lengths. (**b**) The attenuation of the microstrip line. Table 3 summarizes the comparison between the proposed phased array with the other published dual-polarized antenna arrays. Specifically, the antennas based on the waveguide in [13; 14] have low attenuation and high-efficiency characteristics, whereas the problems of heavy weight, high cost, and low integrated level are non-negligible. The metasurface antenna in [16], with lightweight, low feed blockage loss and suitability for fabrication, is designed for the dual-polarized antenna. However, the large focal length-to-aperture diameter radio is not ideal for low-orbit spaceborne applications. Patch antennas with subarray structures are utilized to reduce the T/R RF modules [19; 26]. Beam scanning up to 5\({}^{\circ}\) is achieved for the single linear-polarized radiation in [19]. The microstrip antenna in [26] is able to realize dual-polarization-switched beaming based on the Butler matrix (BM) with a complicated feeding network design. Compared with the same band patch antenna array in [27], the proposed antenna shows high low cross-polarization and isolation. In summary, the high gain, high isolation, low sidelobe levels, and stable radiation performances indicate that the proposed phased array antenna is valuable for low-orbit SATCOM applications. Figure 16: Photographs of the 32 \(\times\) 24 phased array: (**a**) Rx phase-shifting module. (**b**) Tx phase-shifting module. (**c**) Measurement setup in the anechoic near-field chamber. Figure 17: Simulated and measured scanning patterns of the 32 \(\times\) 24 phased array: (**a**) Normalized radiation patterns at 12.5 GHz.