Measurement of Complex-Ratio Between Two RF Signals With Spectrum Analysis

A novel method to measure the amplitude-phase dif-ferences between two radio frequency (RF) signals is presented, based on spectrum analysis after periodic modulation. Two input signals are alternatively selected to enter the single-channel RF channel by a single-pole double-throw (SPDT) switch, which generates harmonics related to the channel unbalance. Amplitude-phase differences between two input signals can be obtained by analyzing the spectrum of received signal using discrete Fourier transform (DFT) in digital domain. Compared to conventional multichannel RF receivers, the proposed method has a concise structure and low-computational complexity. Simulation results are provided to verify its effectiveness over dynamic ranges of 60 dB and 360(?). A L-band RF circuit is fabricated to measure the amplitude-phase differences over 35 dB and 360(?) dynamic ranges. The measured results show good agreement to those by the vector network analyzer (VNA), certifying the effectiveness of proposed method.