# Reconfigurable Multi-Beam Receiver Based on Microwave Photonics Technology
## 2 System Architecture
### Principle of Operation  
The principle of the optimized structure EP is described as follows: The optical switch is controlled to reconfigure the optical path and choose the suitable splitter according to the number of the received beams. After splitting, the optical carriers are sent to the variable true-time delay line units, and the true-time weightings are deployed on the carriers. The multi-wavelength optical carriers from \(N\) AEs are combined at the wavelength division multiplexer to form a received beam. The steps for the configuration of the structure EP are summarized below. 1. Initialization. The system works on the \(M\)-beam mode by controlling the mode-switch and choosing the splitter with \(M\) ports. The \(M\) beams are used to search the signal and cover the range with the angle \(\phi\). Thus, the pointing direction of beam \(m\) has \(\varphi_{m}=(2m-M-1)\cdot\phi/(2M-2)\). The \(m\)-th beam is received from the output \(m\), and the true-time stepping within the \(m\)-th port is \(\tau_{m}=d\cdot\sin(\varphi_{m})/c\). \(d\) is the spacing between the adjacent AEs, and \(c\) is the speed of the light wave in the vacuum. The true-time delay units within the \(m\)-th ports offer the delay vector as \(\boldsymbol{\tau}_{i,m}=[0\,\Delta\tau_{m}\,\ldots\,\,(i-1)\Delta\tau_{m}\, \ldots\,\,(N-1)\Delta\tau_{m}]\). 2. After initializing and signal-searching, we assume that the number of the received signal from different directions is \(K\), and the angles of the received signal are labeled as \(\varphi_{1}\), \(\varphi_{2}\), \(\ldots\), \(\varphi_{k}\), \(\ldots\), \(\varphi_{K}\). The system's working mode is controlled by reconfiguring the optical switch according to the number \(K\). The judgment conditions are described as follows:  
* When \(K=0\), the signals are not received by the system, and the signal searching needs to be performed again by increasing the beam received range. Reconfiguring the optical switch to change the system in order to work on the single-beam mode and the true-time delay line within the first ports periodically offers the delay vector from \(\tau_{i,1}\) to \(\tau_{i,M}\). The beam formed in the single-beam mode has the highest power and covers the largest range. As for the newly received signals, we label them \(\varphi_{1}\), \(\varphi_{2}\), \(\ldots\), \(\varphi_{k}\), \(\ldots\), \(\varphi_{K}\). If the \(K\) is still zero, the signal beyond the system receives the range or is unavailable, and returns to step \(1\). If the \(K\) is changed, the following judges continue to execute;
* When \(0<K<M/2\), we choose the suitable working mode by calculating the parameter \(g\) with \(g=2^{\lfloor\log\!{K}\rfloor}\). We then reconfigure the optical switch to enable the system to work on the \(g\)-beam mode. The outputs \(g\) to \(g+K\) are used to receive the multi-beam. The power of the optical carrier is increased from \(P_{i}/M\) to \(P_{i}/g\)  
Figure 4: The comparison of the parameters when beam number \(N=2,\,4,\,8,\,16,\,32\). (**a**) The comparison of system attenuation with X = 2 dB, L = 3.3 dB; (**b**) The comparison of total number of working combiner-switch. \(P_{i}\) is the \(i\)-th laser power. In the meantime, the delay values are the same as the ports that received the signals at the initial stage., i.e., \(\mathbf{\tau}_{i,k}=\mathbf{\tau}_{i,m}\). The parameter pairs (\(P_{i}/g\), \(\mathbf{\tau}_{i,k}\)) are obtained. * When \(K>M/2\), the system is kept at the \(M\)-beam mode, and all the true-time delay units are set up as the initial stage. The ports that do not receive the signal are used to monitor the original angle. The parameter pairs (\(P_{i}/M\), \(\mathbf{\tau}_{i,k}\)) are obtained from the ports that are used to receive the signal. * Dynamic detection process: when the system is working, we keep the monitor to the parameter \(K\). If \(K\) is changed, we return to step 2. If \(K\) is constant, we continue to monitor.