Study On Monopulse Spread-spectrum Angle Tracking System And Its FPGA Realization

Monopulse radar angle tracking technology occupies an important position inTT&C system. In order to achieve better tracking performance, people combinesmonopulse radar angle tracking with spread-spectrum communication to formmonopulse spreading-spectrum (SS) angle tracking system, which increases the angletracking radar’s ability to adapt harsh environments.The thesis focuses on studing monopulse spreading-spectrum angle errordemodulation. Firstly, the thesis introduces theory of monopulse radar angle errormeasurement. According to the system requirements the whole design scheme isproposed. The system mainly includes the followings, digital down-conversion (DDC),fast AGC loop regulation, pseudo-code (PN) fast acquisition and tracking, carriersynchronous demodulation, signal-noise ratio (SNR) estimation and the angle errordemodulation with interference suppression. Based on software defined radio (SDR)technology, the design analyzes various parts of the system in theory and proposesmathematical model, in which some algorithm are studied. In addition, PC softwaresimulates to demonstrate the feasibility. Through the comparative analysis of outputresults, it proves that system scheme is right.For the characteristics of design system, fast logarithmic AGC algorithm is used tostabilize input signal. For complex logarithmic computation the binary arithmeticlogarithmic algorithm which is based on FPGA is designed to reduce thecomputation complexity.For PN sequence synchronization, the thesis presents fast acquisition algorithm. Inthe section, FFT-based parallel acquisition and digital matched filter (DMF) method areanalyzed, which are faster than the traditional serial algorithm. To save chip logicresources, folded DMF is designed to complete pseudo-code acquisition. Throughtime-frequency two-dimensional searching, large frequency offset acquisition isachieved for carrier synchronization. And lock frequency loop (FLL) completes furtheroffset compensation. Then Lock phase loop (PLL) is used to correct final phasedeviation and the original data is demodulated. In order to improve the speed of phasediscrimination, the thesis adopts21-level pipelined CORDIC algorithm.In the section of extraction angle errors the azimuth and pitch angle errors aredemodulated, which is normalized to eliminate the effect of carrier energy. Meanwhile the sliding window filter reduces angle errors fluctuation that is caused by noise. For thedesign requirement signal-noise ratio of monopulse spreading-spectrum signal isestimated to achieve the selection of radar’s left right input signal. The thesis discussesSNR estimation algorithms in time domain and frequency domain and presents theestimation methods for the design system. By comparing SNR of radar signals, theazimuth and pitch angle errors of high SNR branch are used.Finally, the system adopts Verilog HDL language to achieve the hardware circuitdesign in the hardware platform. By simulation tool, the performance of the system isverified. After program is synthesized to download in the FPGA chip, monopulsespreading-spectrum angle tracking system is tested in the real environment. The workresults show that design system is running normally and can meet the practicalrequirements.