Research On Key Technology For Digital Beamforming Network In Satellite Based On Polyphase Filter

In this paper, two key technologies in on-board reception digital beamforming network are studied, including digital orthogonal down converter and digital demultiplexer. Digital orthogonal down converter and digital demultiplexer based on polyphase filter can significantly reduce the equipment complexity and slower the processing speed to facilitate the real-time signal processing.In digital orthogonal down converter, the local oscillator error would affect its performance. When sampling rate is high, the low pass filter (LPF) order will be too great to be realized in hardware. But digital orthogonal down converter, which is based on polyphase filter, doesn’t need local oscillator and its LPF order is much lower. So the realization structure is relatively simple. In digital demultiplexer, when the number of frequency bands is equal to decimation ratio, the structure of polyphase filter is efficient and easy to be realized. However, its application scenario is limited. In this paper, an improved polyphase filter has been designed. This filter changes the way of datas to enter storage units before polyphase filter and provides a data-shift operation before FFT. So it can be easily applied in the case where the channel decimation is unrelated to the number of frequency channels and break through the application limitation that polyphase filter is generally used in the cases that the number of frequency bands is always equal to the decimation ratio. Therefore, this improvement makes polyphase filter much more flexible and has a wide range in application.In this paper, MATLAB simulation experiment using 256-channel FDM/QPSK signal have been done aiming at two technologies. After that, the detailed FPGA design idea, optimization structures and realization results have been given. The FPGA realized results consistent with the MATLAB simulation result proved the correctness and feasibility of designed theory models.