Abstract: Aimed at large volume, heavy weight of the existing mode S transponder, thus it is not applicable to small general aviation aircraft especially small UAVs（Unmanned Aerial Vehicles）, a new mode S transponder of general aviation is designed. The system adopts all-FPGA（Field Programmable Gate Array） design, the state machine is used to approach the realization of encoding and decoding function, a digital filter for the signal is designed by pulse width filtering method. The test results show that the system works stably, response of the interrogation signal is realized, and meets the RTCA DO-181D and DO-260B standards. For the system’s advantages of small volume, light weight, low cost, it is suitable for the general aviation aircraft whose interior space is limited.

Key words: mode S transponder, Field Programmable Gate Array（FPGA）, general aviation, state machine, digital filter

摘要： 针对现有S模式应答机体积、重量过大，不适用于小型通用航空飞机尤其是无人机的现状，设计了一种用于通用航空的新型S模式应答机。系统采用全FPGA设计，用状态机的方法实现编码、解码功能，使用脉冲宽度滤波的方法对通讯信号进行了数字滤波。实验结果表明：该系统工作稳定，实现了对询问信号的应答，符合RTCA的DO-181D及DO-260B标准；并且具有体积小，重量轻，成本低等特点，适用于内部空间有限的各种小型通用航空飞行器。

关键词: S模式应答机, 现场可编程门阵列（FPGA）, 通用航空, 状态机, 数字滤波