Passive Detection System And Its Key Technology

Nowadays, the active single base detection system facees four threats of"electronic interference, anti-radiation missile, super low air penetration and stealthtechnology” because of the rapid development of electronic warfare technology. Thepassive detection system mainly uses the related detection theories of electromagneticwave and signal processing technology to acquire the non cooperationelectromagnetic echo signals reflected by a target, and this may be a comprehensiveapplication and integrated system for electromagnetic wave information in space. Byreceiving echo signals passively, analyzing and dealing with target scattering signalsfrom the external emitters, so as to realize the target detecting, locating, tracking andrecognizing, hence, it’s also called as passive radar, bistatic radar, the non cooperationilluminator source radar or non-cooperative passive detection system. Compared withcommon active detection system, the passive detection system is characterized withthe anti-interference, anti-radiation missile, anti super low penetration and anti-stealthpotential (so-called" four counteraction") and the characteristics of good elusive, highability of battlefield survival and low air detection, system structure is simplerelatively, not need to take up frequency spectrum resource, can use all sorts of civilsignal as detection radiation source. Therefore, passive detection system is paid closeattention and vigorously developed, and has more and more vital significance in themodern electronic warfare. This paper studies on a passive illuminator detectionsystem based on the GSM base station signal as the non cooperation source. Thesystem is divided into three key technology links that is antenna, digitalized receiverand data processing algorithms, respectively. And aims at weak target electromagneticwave signal detection for developing and analysis, and completed the followingresearch work:Antenna is the first key link for capturing the weak electromagnetic signalreflected by the air targets. The micro strip array and related technology was studied,and a weak coupling method was used to effectively reduce the amplitude side lobe of micro strip array. The diagonal loading pattern control algorithm DLAPC was putforward to improve the efficiency of the commonly used DBF processing.Considering for the factors such as cost, designed and implemented the8elementsmicro strip array, used software Matlab for its simulation, completed the array process,test and correction. The processed micro strip array is with features of the beam widthless than15o, gain more than38.9dBi, side lobe level less than12.8dB, and hasbroadband, high power gain, wide band, small volume, light weight, good flexibility,high reliability, and laid a good foundation for the weak signal detection processing.The receiver is another important part for amplifying the signals received by arrayantennas, to complete frequency conversion, analog-to-digital converting，etc., and gethigh SNR of the data for next stage. Research on the basis of radar receiver sourcerelated technical theory. According to the software defined radio theory, the FPGAfrom Altera Company was used to design and realize GSM passive digital receiver.The system scheme was implemented and the2order PLL (Phase Locked Loop) wasdesigned to improve the stability of PLL and error in the loop was evaluated andanalyzed under extreme conditions such as a step signal was input. Simulation andindoors test were made for the receiver. Test results show that the input and outputsignal waveform has good consistency, the input signal dynamic range of thereceiver was60dB, sensitivity for-120dBm, Automatic Frequency Control (AFC)capture range for±250KHz. And all of these validate the system function andperformance had satisfied the design requirements.Data processing plays an important role for target detection. Firstly, studied themathematical model of GSM signals, analyzed its ambiguity and characteristics, andevaluated the feasibility of thumbtack structure of GMSK modulation signal forpassive detection. In order to improve the signal-to-noise ratio and the weak signalprocessing efficiency, the combining method of higher order fuzzy function and twothreshold detection was used. First, proposed a high order fuzzy function algorithm.The GSM polynomial phase echo signal parameters were estimated, and withMonte-Caro algorithm testing results are compared. It was verified that the high orderfuzzy function can effectively estimate the parameters of GSM polynomial phase of the echo signal, and with small burden, simple and high efficiency. Second, for thereason that the high order fuzzy function algorithm requires higher SNR, so designeda two thresholds detection method to eliminate noise interference and improvesignal-to-noise ratio: most of the noise in each frame was eliminated in thepretreatment by time domain method, and the remained noise was eliminated as frameaccumulation. After two thresholds processing a weak signal was processed moreeffectively, meanwhile reduced the computational complexity and storage capacity,and improved the real-time signal processing.Using the grey theory to improve the Extended Kalman method, and solved thedivergence problem of the EKF when tracking a maneuvering target. With the greyKalman algorithm, the simulation and experimental validation of targets was done toverify its feasibility.At last, the field test was made for the designed passive detection system. Thefield was selected near Wuhan Tianhe Airport, measure the Doppler frequency of theplane in taking off stage, one of the most is390Hz, calculated out the speed wasabout220kilometers per hour, and approximate to the actual take-off stage speed. Thebiggest detection distance for a civil aviation plane was about3.0km, test wasbasically successful.The passive detection system based on the non cooperation radiation source ofGSM signal, can be used as effectively complement to city air defense radar network,to detect goals breakthrough other air defense network, such as the helicopter, airship,cruise missiles, etc. In addition, a single GSM passive detection system may be usedas a node and many node may be connected with communication links to construct adistributed GSM passive detection system network, so can build a greater range ofpassive detection network, so it ’s to have the important meaning as to improve theurban air defense ability. And this system may also be used for detecting vehicles onthe road or river.