In this article, we present a vector network analyzer (VNA)-based measurement scheme and setup to obtain repeatable phase spectrum measurements of 75–110-GHz modulated radio frequency (RF) signals. In order to remove the random phase contribution of sweeping local oscillator (LO) in harmonic downconversion, the LO signal is coupled out into an auxiliary measurement channel where its random phase at the fundamental can be derived after additional modulation and downconversion treatments. Afterward, a user-defined math equation is used inside the VNA for LO phase cancellation, based on the traces of RF- and auxiliary-channel raw measurements. The key point of the proposed LO phase cancellation technique is measuring the 75–110-GHz test signal and the auxiliary-channel signal at the same GHz intermediate frequency so that the receivers of VNA can measure both of them simultaneously when working on the peculiar continuous-wave or zero-span mode. According to the method validation at 78, 93, and 108 GHz, a phase fluctuation of ±2° for single-run measurements is found reachable in practice.

中文翻译：

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使用基于 VNA 的 LO 相位消除技术对 75-110 GHz 调制信号进行可重复相位频谱测量

在本文中，我们介绍了一种基于矢量网络分析仪 (VNA) 的测量方案和设置，以获得 75–110 GHz 调制射频 (RF) 信号的可重复相位频谱测量。为了去除谐波下变频中扫描本地振荡器 (LO) 的随机相位贡献，LO 信号被耦合到一个辅助测量通道中，在该通道中可以在额外的调制和下变频处理后导出其基频的随机相位。然后，根据射频和辅助通道原始测量的轨迹，在 VNA 内部使用用户定义的数学方程来消除 LO 相位。所提出的 LO 相位抵消技术的关键点是在相同的 GHz 中频测量 75-110-GHz 测试信号和辅助信道信号，以便 VNA 的接收机在工作于特殊连续-波或零跨度模式。根据 78、93 和 108 GHz 的方法验证，在实践中发现单次运行测量的相位波动为 ±2°。