Broadband Phase-coded Signal Digital Channelized Receiver And Technology Research

Desirable characteristics of an electronic warfare (EW) receiver include: wide band frequency coverage, high sensitivity and dynamic range, high intercept probability and simultaneous signal detection and fine frequency resolution. Digital channelized receiver is an EW receiver that almostly provides all these requirements. There are two difficulties when applying the channelized receiver to intercept a broadband phase coded signal (PCS). Firstly, it is difficult to detect the PCS because of its characteristics of strong autocorrelation and low sidelobe.The second is that two or above channels are possibly occupied by the PCS caused by its spread spectrum. Two schemes of digital channelization are proposed to verify and solve the aforementioned problems based on the investigation of the interaction mechanism of the PCS signal and channels.The main results are as follows:1. The importance of intercepting a PCS of pluse radar and the advantages of a digital channelized receiver are discussed based on signal characteristics under modern electronic reconnaissance environment.2. Some characteristics of PCS, such as waveform, spectrum, autocorrelation and ambiguity function, are analyzed. It's critical to reconstruct code sequence and measure subcode width from the received PCS. Since short time Fourier transform (STFT) is the base of channelization, so the adaptability to wide and narrow signals is the key for a digital wideband channelized receiver to intercept phase coded signal.The structure of this receiver are investigated in detail.3. It's pointed out that crosstalk between adjacent channels will occur when intercepting a broadband PCS, the narrow channel will lose most enegy of signal's, and the signal integrality is destroyed, based on the study of the interaction mechanism of signal and channels. It is not difficult to reconstruct code sequence and measure subcode width only when the mainlobe energy is captured mostly by channel.4. A polyphase filter bank is designed and the selection of its key parameters is also introduced. An improved FFT arithmetic is given to realize digital downconversion in channelization, as a result a half of hardware consume is reduced by appling N/2 point FFT to implement N point FFT. Methods of signal detecting are studied and an improved method of average instantaneous frequency measurement (IFM) is given. An approach to detect channel, that using enengy detection to judge whether there do exist signal in the channels and to identify phase-hop by using amplitude detection and IFM, is presented and verified. Methods of reconstruct milti-channel signal are studied and a synthesis filter bank is designed and verified to be effective.5. Two schemes namely digital channelization based on time-frequency analysis and milti-step digital channelization are proposed based on the study and FPGA design of key modules such as polyphase filter bank, FFT and the channels detection, some important time simulation and arithmetic flow are given. The system hardware design is presented, the details of high speed ADC, PCB of digital channelization and high speed data transmitting are analyzed, and some important design fundamentals are also given.