# Reconfigurable Multi-Beam Receiver Based on Microwave Photonics Technology
## 3 Numerical Simulations  
A series of numerical simulations were performed to validate the proposed architecture's performance in MATLAB. The simulation work developed closely follows the architecture as presented in Figure 3.  
The tested phased array antennas (PAA) are settled for a uniformly distributed linear array containing 16 AEs, spaced by half the RF signal wavelength. All the AEs are considered isotropic, and the exciting power is 0 dBm. The frequency of the RF signal is set at 60 GHz. The system support three modes: the single-beam mode, dual-beam mode, and four-beam mode. Under ideal conditions, the optical switch and the optical splitter are lossless. No extra phase difference will be caused when the signal passes through the optical components. The multi-beam patterns when the receiver works in three modes in such conditions are plotted in Figure 5.  
In Figure 5, when the receiver is working in the single-beam mode, the minimum true-time delay \(\Delta\tau=0\), the beam direction is \(0^{\circ}\), and the main lobe power is 24.08 dBm. When the receiver is working in the dual-beam mode, the minimum true-time delay \(\Delta\tau=\pm\) 4.17 ps, two beams point toward \(\pm\)30\({}^{\circ}\), and the main lobe power is 18.06 dBm. Figure 5: The multi\(-\)beam pattern in ideal condition. (**a**) single\(-\)beam mode; (**b**) dual\(-\)beam mode; (**c**) four\(-\)beam mode. When the receiver works in the four-beam mode, the true-time delays \(\Delta\tau\) are \(\pm\)2.16 ps and \(\pm\)5.89 ps, respectively, the beam directions are \(\pm\)15\({}^{\circ}\) and \(\pm\)45\({}^{\circ}\), and the four main lobe powers are 12.09 dBm. One conclusion can be drawn by comparing the main lobe power, which is the greater number of the received beam; the main lobe power is lower. Thus, the optical energy can be focused on the beam that is needed to receive by switching the working mode of the system and controlling the signal fed to a suitable splitter. It should be noted here that the four-beam mode has the same performance as the conventional four-beam receiver in ideal conditions. However, in reality the switch and splitter elements will cause differences in the optical path within and between the output ports. The differences are described as amplitude and phase inconsistency and will influence the quality of the received beams, such as deviating the beam direction, decreasing the main lobe power, and degrading the side lobe suppression ratio. The simulations were performed to evaluate how the introduction of reconfigurable structures affects conventional structures. The amplitude inconsistency is caused by the additional loss of optical components and the split loss of the splitters. We set those contributions as a random positive value \(a_{1}\sim\) U (0, 12\({}^{1/2}\)), which is a uniform distribution with a variance of 1 dB. The switching speed of the optical switch, the fabrication imperfection of optical components, and the delay accuracy of true-time delay units will cause phase inconsistency. These contributions were set as a random value \(p_{1}\sim\) U (\(-\)12\({}^{1/2}\), 12\({}^{1/2}\)), a uniform distribution with a zero-mean and a variance of 1 ps. The amplitude and phase inconsistency are added on to 16 AEs, and the simulation results are plotted in Figure 6.  
As seen in Figure 6, when the system works in the single-beam mode, the power of the main lobe decreases to 20.59 dBm, and the deflection angle to the pointing direction is 0.4\({}^{\circ}\). When the system works in the dual-beam mode, the powers are lowered to 14.28 and 13.52 dBm, respectively, and the angles of deflection are 0.2\({}^{\circ}\) and 0.3\({}^{\circ}\). When the system works in the four-beam mode, the powers are decreased to 9.05, 8.64, 8.41, and 8.31 dBm. The angles of deflection are 0.7\({}^{\circ}\), 0.1\({}^{\circ}\), 0.1\({}^{\circ}\), and 0.2\({}^{\circ}\). Compared to the beam pattern in the ideal condition, the introduction of the reconfigurable structure declines the quality of the multi-beam.