Design And Implementation Of Wideband Intermediate Frequency Signal Processing System

Electronic countermeasure technology becoming more and more important in modern information warfare where receiving and processing of radar signals is a research hotspot.With the development of radar technology, the complexity of modern electromagnetic environment is increased, signal environment is intensity, the situation is complex and parameter is fast changing. This requires that the digital receiver must have wide frequency range, high sensitivity, large dynamic range, multi-signal parallel processing and real-time signal processing capacity are essential.In this paper,the design is based on passive radar signal processing system and discussed from the structural design of channelized receiver and process signal of the rear-end in order to put forward a design scheme in which channelized receiver is wideband,high sensitivity and large dynamic range. Wideband intermediate frequency signal processing system is mainly used in the passive radar system, the goal is to detect active radar after acquisition radar signal for giving the phase, frequency and type of the signal by finding direction of signal to determine the location information of target radar. In the design, the factors of data capture and signal process restrict the development of wideband digital receiver. With the increase of the signal bandwidth, the high sample rate made stringent requirements which are not only for speed and precision of ADC, but also for back-end signal processing and for the difficult design of whole system.In order to solve the above problems, this paper combine traditional finding and frequency measurement with digital signal processing technology, using ADC of high sampling speed, high precision and FPGA of high speed so that wideband digital channelized receiver have advantages of high accuracy, high resolution, and strong ability to identify and so on. Wideband signals are firstly through ADC conversion directly, then channelized processing by digital receiver to solve the bottleneck problems of high speed ADC and backend signal processing which is in case of broadband signal receptionb, according to the information of IQ which is output signal of channelized to obtain the phase, amplitude,frequency,then measured direction of broadband signal and recognition the pulse modulation feature.The main contents and innovation of this paper:Firstly, the key technology of passive radar signal processing was studied and the structure of efficient channelized which is based on polyphase filter is derived. Simulations illustrate the correctly of this structure and the frequency measurement algorithms are analyzed. For the problem of wideband signal direction finding,this paper propose a dual frequency defuzzifiedm based on channelized and combine direction finding of wideband signal with channelized, improve the accuracy of wideband signal direction.Secondly, identified the type of radar signals is a key problem in electronic reconnaissance and common radar signals is analyzed. The type identification methods according to different pulse characteristics of frequency modulated signal and phase modulated signal is proposed. The identification method of VFM signal and SFM signal was proposed which is the innovation of this paper.Again, using ADC and FPGA to construct the hardware design of wideband intermediate frequency signal processing system and giving software design processing of FPGA,real-time processing of wideband intermediate frequency signal is realized and procesing time is less than 10us.Finally, the performance of wideband intermediate frequency signal processing system is tested in the hardware test platform and the results are given.