Electrical Alignment Technique for Offset-Mounted and Arbitrarily Oriented AUTs in a Robot-Based mm-Wave Antenna Test System

One of the main advantages of a robot-based antenna measurement systems compared to traditional positioning systems like roll-over azimuth positioners are the additional degrees of freedom and, thus, the increased flexibility with respect to the sampling grid and the placement of the antenna under test (AUT). However, this flexibility also requires a precise alignment of probe antenna and AUT to obtain accurate measurement results. In this paper, an electrical alignment technique based on a six term error model is introduced. The misalignment errors are estimated from measurement of single
$$\theta$
-cuts of a reference AUT, using a least-squares optimization approach. The estimation results can be used subsequently to correctly align the probe antenna to the physical position of arbitrary AUTs, independent of the sampling grid. The technique is validated by measurements in the mm-wave frequency range. Results show that the proposed method allows a correction in the same order of magnitude as the repeatability of the robotic system, therefore contributing to an increased overall accuracy of the obtained measurement results.