| The S-mode transponder is an Airborne equipment developed based on the traditional A/C transponder.It is used to receive and identify the inquiry signal transmitted by the ground secondary radar and then to answer the aircraft flight status information.Therefore,in the field of air traffic control,transponder equipment plays an irreplaceable role.With the rapid development of China's economy and the improvement of people's living standards,the density of aircraft in the airspace is increasing,and the demand for the national air transport industry is also increasing.The problem of “synchronous crosstalk” in the response signal of traditional A/C transponders is becoming more and more prominent.Secondly,the 4096 IDs that can be represented by 12 symbols are far from meeting the requirements for the number of aircraft in the current airspace.The S-mode transponder can assign an independent address code to each aircraft.The data link of the S-mode signal is assigned 24 bits to represent the aircraft's address code,and a total of 16,777,216 aircraft address codes can be allocated,which can achieve "one-to-one" questions and answers,without the influence of multiple aircraft distances and azimuths,overcame the A/C transponder's synchronous crosstalk and overload problems.Therefore,the installation of an S-mode transponder has become the primary is in current air traffic control.However,at present,the domestic S-mode transponder equipment mainly relies on imports,and its key technologies are still subject to the developed countries such as Europe and the United States.Therefore,the current development of the S-mode transponder is imminent and of great significance.This subject comes from the actual development project that the author takes part in during the internship of the China Electronics Science and Technology Group Northwest Co.,Ltd.,and I am mainly responsible for the digital processing of the S-mode transponder signal in the project.Combining with the analysis of the development status and existing problems of the current S-mode transponder at home and abroad,the paper presents a new design of airborne S-mode transponder signal processing system.The system is based on the Software Radio Design Ideas,which directly digitizes the 70 MHz IF output from the RF receiver,completes the demodulation and pattern discrimination of the S-mode transponder inquiry signal,and then completes the response data encoding in the current mode.Firstly,the paper proposes the recognition technology of different modes inquiry signals for S-mode transponder,and then carries out detailed theoretical research and MATLAB simulation analysis of the DPSK demodulation technology of S-mode IF data link.Based on this,it aims at the burst characteristics of S-mode data,proposed a new algorithm that could complete local carrier extraction quickly in the DPSK demodulation loop.The feasibility of the algorithm is verified by MATLAB modeling and simulation.After completing the research on the key technologies of the system,the paper describes the hardware platform of airborne S-mode transponder system,and describes the overall data processing flow,task division and design of each part of the system.Since the author focuses on the design and implementation of the FPGA part in the project,the paper focuses on the processing of signals on the FPGA hardware platform,and describes in detail the design and implementation of IF demodulation,baseband signal pattern discrimination,and response signal coding.Finally,through the simulation verification,board-level debugging and performance testing of the basic functions of the system,it shows that the system meets the basic functional requirements of S-mode transponder that the international civil aviation ANNEX 10 ruled.The design scheme of the S-mode transponder signal processing system that proposed in this paper has the characteristics of accurate decoding,low cost,and strong portability. |
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