The Design And Implementation Of Signal Source Based On DDS For Perimeter Detection System

Various terrorism activities appear frequently,and the situation of border security has become increasingly severe.At the same time,the demand for people's sense of security has also increased with the development of science technology and society.Therefore,it is required to have an environmental suitability security system with detection and alarm functions to provide security protection.The perimeter intrusion detection system based on leakage coaxial cable is a new type of security equipment with burring the detection sensor in the ground to form an electromagnetic detection area.The electromagnetic field in the detection area of this system is invisible and unavoidable.Therefore,the difficulty of intruders bypassing the security equipment is greatly increased.Perimeter intrusion detection system has many advantages in the field of military security and civilian security,such as no blind area,high concealment,all-weather work,and strong environmental adaptability.The signal source designed and implemented in this thesis is an important part of the perimeter intrusion detection system.The quality of the transmitted signal is a key factor affecting system sensitivity and false alarm rate.The signal source function is to generate a variety of required signals during system testing and application,which has the advantages of high resolution,high accuracy,high agility speed,continuous signal phase,and multiple modulation methods(such as linear frequency modulation and phase encoding).Firstly,the principle of the perimeter detection system based on the leaky cable is studied and the characteristics of the detection signal are analyzed in this thesis.Then,the theoretical basis of the direct digital frequency synthesis technology and its spectrum overlapping phenomenon are studied.The characteristics and control methods of DDS chip AD9910 are introduced.The feasibility of signal source FPGA+AD9910 scheme was analyzed,and the specific method of the design scheme was given.Finally,the hardware circuit design of the signal source and the FPGA program design are realized.The hardware circuit includes the reference clock,power supply circuit and AD9910 control circuits and low-pass filters.FPGA program is designed by a Top-Down modularity method in this thesis,and the program structure level is clear,easy to debug and modify.The most important module is the signal encoding module,the module's main function is to configure the AD9910 various registers and control the transmit signal form,pulse width,and PRI values.The test results of signal source show that the frequency resolution of the signal source designed and implemented in this paper can reach 0.24 Hz,the maximum output frequency can reach 400 MHz,the frequency accuracy is less than 0.05%,and the signal waveform is good.The signals include sine wave,LFM continuous wave,LFM pulse and phase modulation pulse.The signal source performance index meets the design requirement of the system,and has the advantages of simple and reliable circuit,easy reuse and expansion,and high cost performance.