Misalignment measurement is important in radio frequency orbital angular momentum (RF-OAM)-related communication and radar applications. Misalignment causes distorted vortex wavefront and OAM spectra dispersion, therefore a conventional gradient method cannot be used directly. We propose a misaligned measurement method for RF-vortex beams based on image processing. Theoretical analysis and numerical simulations of the misaligned OAM wavefront demonstrate that the misalignment information can be measured by extracting the features of the OAM mean value distribution and the OAM variance value distribution. It is found in this paper that the extrema of mean OAM distribution and OAM variance distribution correspond to the tilted singularity point and original pivot point, separately. These extrema points can be found by image processing algorithms that recognize round speckles. A proof-of-concept experiment is presented, which employs a 2-D scanning probe to measure a 10°-tilted OAM beam with mode +1. The tilt measurement error is only 0.39°.

中文翻译：

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基于频谱分析和图像处理的轨道角动量信号错位测量

未对准测量在与射频轨道角动量 (RF-OAM) 相关的通信和雷达应用中很重要。未对准会导致涡旋波前失真和 OAM 光谱色散，因此不能直接使用传统的梯度方法。我们提出了一种基于图像处理的射频涡旋光束未对准测量方法。未对准OAM波前的理论分析和数值模拟表明，可以通过提取OAM均值分布和OAM方差值分布的特征来测量未对准信息。本文发现平均OAM分布和OAM方差分布的极值分别对应倾斜奇异点和原始枢轴点。这些极值点可以通过识别圆形斑点的图像处理算法找到。提出了一个概念验证实验，该实验采用二维扫描探头测量模式 +1 的 10° 倾斜 OAM 光束。倾斜测量误差仅为0.39°。