一种降低数字式FM/FM解调系统分路滤波器阶数的方法

Method for Reducing the Order of Demultiplex Filter in Digital FM/FM Demodulating System

FM/ FM遥测体制有着广泛的应用 ,研究数字式 FM/ FM解调系统具有重要意义。分路滤波器 (通常是带通滤波器 )是解调系统的重要组成部分 ,有限冲激响应 (FIR)数字滤波器具有平坦的通带幅度响应和线性相位特性 ,是数字式解调系统的最佳选择。但是 ,符合 IRIG标准的分路滤波器通常是窄带滤波器 ,需要很高的阶数 ,这给系统的实现带来了很大的困难。文中根据变采样率多级实现 FIR滤波器的原理和带通信号采样定理 ,并结合 FM/ FM系统 IRIG标准中各路信号的频谱特性提出了先按频谱分割进行预滤波 ,再降低采样率滤波的方法 ,有效地降低了 FM/ FM系统分路滤波器的阶数。

FM/FM telemetry systems have been widely used in many aspects,so it is very important to study Digital FM/FM Demodulating System(DFDS).Demultiplex filter(usually refers to bandpass filter)is a significant part of DFDS,while the flat frequency response and linear phase characteristic in the passband of the FIR filter make it the best choice for the system.Because the demultiplex filters that meet the IRIG specifications are usually narrowband filters,so it requires a higher order and there is a big difficulty to implement.Based on the theory of multistage approach to FIR filter and the sampling theorem for bandpass signals,combining with spectrum characters of IRIG FM/FM system,a new method is proposed.In this method,the spectrum is firstly divided into several parts through Pre filtering,and then another filtering is proceeded at a lower sample rate.This method can efficiently reduce the order of demultiplex filter in DFDS.