在雷达、声纳、通信等电子系统中,传输信息的信号通常是窄带信号,即 B(?)f(?)其一般表示式为a(t)=ρ(t)cos[2πf_ct+θ(t)]信号的频谱集中在 f=±f_c 附近,f_c 为载频。带通信号的幅度ρ(t)和相位θ(t)表征了带通信号的调制成分。它们相对于载波周期1/f_c 来说是一个慢变化的函数,但要直接在 f_c 频率上用数字硬件来处理这些信号尚有一定困难。由于信息集中在调制成分中,因此可集中研究它的调制成分。对高分辨率雷达、动目标检测雷达、声纳、数字交换系统,通常只需检测信号振幅ρ(t)的信息。为此可采用正交复调制的方法,把带通信号变换成两个正交的低通信号进行研究。这样研制数字硬件时就有实现的可能。对带通信号作正交展开 In radar, sonar, communication and other electronic systems, the signal transmission information is usually narrowband signal, which is generally expressed as a (t) = ρ (t) cos [2πf_ct + θ t)] signal spectrum concentrated around f = ± f_c, f_c for the carrier frequency. The amplitude ρ (t) and the phase θ (t) of the bandpass signal characterize the modulation component of the bandpass signal. They are slowly changing functions relative to the carrier cycle 1 / f_c, but there are some difficulties with using digital hardware to process these signals directly at f_c. Because information is concentrated in the modulation component, it can focus on its modulation components. For high-resolution radar, moving target detection radar, sonar, digital switching systems, usually only need to detect the signal amplitude ρ (t) of the information. To this end can be orthogonal complex modulation method, the bandpass signal into two orthogonal low-pass signal to study. This development of digital hardware is possible to achieve. Bandpass signal for orthogonal expansion