Research On Bandwidth-Matched Digital Reconnaissance Receiving

Wideband digital receiver has been a trend of the development of Electronic Warfare (EW) reconnaissance system. Its characteristics are using high-speed ADC closing to RF front-end to cover a wide survey band, and using data rate converter to decrease data rate and implement distortionless receiving, and then using DSP to implement precisely parameters estimation for low-speed data. However, there is a great challenge that the speed mismatch between front-end high-speed ADC and back-end low-speed DSP for the realization of wideband digital receiver. In electronic reconnaissance, prior information of the target signals isn't provided in the complicated electromagnetic environment. The baseband signal rate of matching bandwidth is the lowest data rate in distortionless condition, so how to further decrease data rate and signal processing load, and implement distortionless bandwidth-matched receiving has been the key technique and difficulty for digital reconnaissance receiver. This dissertation focuses on the theoretic foundation, architecture and realization of bandwidth-matched digital reconnaissance receiving, and the interrelated key techniques and difficulties. The main contributions of this dissertation concentrate on a few aspects as follows:1. It is researched that the theoretic foundation, system design and realization of bandwidth-matched digital reconnaissance receiving in EW environment. It is proposed that six bandwidth-matched receiving schemes, such as bandpass sampling, digital downconversion (DDC), digital channelizer, leading spectral synthesis, spectrum time-sharing receiving for long pulse signals, and spectral compression. The advantage and disadvantage of them are analyzed while the key techniques and difficulties are discussed. Frequency and bandwidth estimation methods in bandwidth-matched receiving are also discussed, and some methods with good realizability are given.2. Bandwidth-matched digital receiving methods based on bandpass sampling are studied. Two bandwidth-matched digital receiving structures, variable-speed direct ADC bandpass sampling and variable-speed direct bandpass decimation, are proposed. However, these structures suffer from system performance worsening. To overcome these problems, some modified ways are presented. Meanwhile, the difficulties in hardware implementation are also analyzed, and some results show that the latter structure has better realizability.3. Bandwidth-matched digital receiving methods based on the efficient structure of DDC are studied. Based on multistage decimation ratio and rational decimation ratio, an efficient variable-bandwidth DDC and an efficient bandwidth-matched receiving method are proposed, respectively. Based on polyphase filtering structure, they achieve a significant reduction in complexity and computational cost. Finally, bandwidth-matched receiving methods are discussed for multiple simultaneous signals, and solutions for hardware implementation are given.4. Bandwidth-matched digital receiving methods based on variable-bandwidth filters (VBF) are studied. Firstly, a linear programming design technique is proposed for designing the variable-bandwidth linear-phase FIR filters in the weighted minimax sense. Then, it is presented that an efficient weighted-least-square (WLS) design method for FIR digital filters with variable bandwidth whereas the phase response is stable. Furthermore, a design technique of VBF based on the extended Fourier transform (EFT) and an efficient bandwidth-matched receiving structure based on EFT filters are proposed, respectively. The above VBFs are implemented with the aids of only one variable spectral parameter that determines the bandwidth and a simple updating routine. Finally, bandwidth-matched receiving methods based on VBF are discussed for multiple simultaneous signals.5. Bandwidth-matched digital receiving methods based on spectral compression are studied. Firstly, it is introduced that the foundation of spectral compression and reconstruction. Then, the frequency-warped characteristic of Laguerre transformation and its spectrum-compressed characteristic for LFM signal are analyzed. A novel spectrum-compressed digital receiving method using Laguerre transformation for LFM signal is proposed. The spectrum-compressed signal can be reconstructed by using the spectrum-reconstructed network. The modulation rate and initial frequency of the spectrum-reconstructed LFM signal can be estimated precisely.6. Design and Implementation of the bandwidth-matched digital receiving experimental systems, including the total scheme, high-speed A/D board, bandwidth-matched receiving processing board, PCI data acquisition card, parameters estimation processing board, and display and control software, are introduced. The test results show the experimental system has better performance and can validly implement signal bandwidth-matched digital receiving.