# Reconfigurable Multi-Beam Receiver Based on Microwave Photonics Technology
## 1 Introduction  
The beamformer will become the key component in future telecommunications with the deployment of mobile broadband, the large-scale Internet-of-Things (IoT), self-driving cars, telemedicine, and cloud-gaming [1]. To better offer such services, the next generation of wireless communication will need to expand the spectrum and explore a new dimension: spatial-division multiplexing (SDM). With SDM, each user may access the entire spectrum without interference. Thus, implanting SDM is becoming a hot topic in research. The design of the broadband antennas [2] and the multi-beamforming [3] to support the SDM are two promising directions. Moreover, using the photonic beamformer as the broadband multi-beam signal processing has its own advantages and huge potential. The beamformer built by microwave photonics technology inherits the advantage of microwave photonics, such as low loss, wide bandwidth, and immunity to electromagnetic interference [4, 5]. Realizing the true-time delay line in optical circuits is simpler than in electronic circuits [6, 7, 8, 9]. The beamformer based on the true-time delay can effectively eliminate the beam-squint effect and is more suitable for the next generation of wireless communications. Furthermore, optical beamformers can easily form multi-beams by incorporating wavelength division multiplexing (WDM) because the splitting in the optical domain is not limited by the signal bandwidth.  
Numerous studies have reported on the optical beamformer architecture to support multi-beam antennas [10, 11, 12, 13, 14, 15, 16]. Four independent beams with eight scan angles were realized using a large port-count demultiplexer and fast-tunable lasers [12]. The beamformingnetworks built as the optical Blass matrix architecture in phase shifters and Mach-Zehnder interferometers to generate three beams simultaneously pointing in different directions were realized [13]. The whole array was divided into multiple subarrays, and each subarray was used to form a beam that also achieves the one array transmitting multi-beam simultaneously. But it is not multi-beamforming in the strict sense [14]. Recently, using programmable photonics processors to manipulate the WDM optical signals to achieve multi-beam antennas has been reported [15].  
However, these architectures only achieved the multi-beam architecture in which the number of beams is fixed. this means that the system affords constant optical power overhead and cannot adapt to the various scenarios in future communications. For example, when the number of users or the distance between the base station and the user is changed, the above structure may not offer high-quality services. To overcome this shortcoming, designing a multi-beamforming architecture in which the number of beams is reconfigurable is necessary.  
In this manuscript, we proposed a multi-beamformer architecture with a variable beam-count by introducing the reconfigurable optical switch and the variable splitter into a conventional space multiplexing multi-beam architecture. We reconfigured the state of the switches dynamically to split the optical carrier according to the needs of current scenarios. This method focuses the optical energy into the beams that need to be received and improves the system's energy efficiency. This manuscript includes the process of designing and optimizing the beamformer architecture, followed by theoretical analysis and multi-beam pattern simulation. The numerical simulation result confirms that the system with a variable beam-count has high energy efficiency and adapts to future communications smartly.