结合对带通采样定理的理解，讨论了直接中频带通信号采样正交检波的基本原理，重点探讨正交混频低通滤波法和希尔伯特变换频移法。利用对带通采样定理的理解，扩展其应用范围，给出了适用条件、原理框图以及信号流图。最后用仿真实例验证了扩展方法的可行性，对工程实际有一定的参考意义。

Fundamentals of IF(Intermediate Frequency) bandpass signal sampling and quadrature detection are discussed,especially the coherent mixing LPF method and Hilbert transform frequency-shift method.In-depth comprehension of bandpass sampling theorem allows expanding the application fields,and applicable condition,principle diagram and signal-flow graphs are given respectively.These results help to understand and utilize quadrature coherent detection.Finally,simulation examples are given to validate the effectiveness of proposed methods.

TN957.51