Highly Efficient Angular Array Calibration Based on the Modal Wave Expansion Technique

In the upper millimeter wave range above 100 GHz, the effect of array imperfections like manufacturing uncertainties and mutual antenna coupling increases, which leads to deviations from the nominal antenna positions and angle-dependent errors in direction-of-arrival (DoA) estimation. The proposed calibration procedure aims to correct the assumed array response model, based on nominal antenna positions and therefore to improve the measurement accuracy of the array. Typically, the calibration parameters are obtained by interpolating a data set consisting of calibration measurements at known angles. The required number of measurement points in the calibration procedure increases with larger array size, which makes array calibration very time-consuming and costly. In this article, a highly efficient angular array calibration procedure is proposed based on the modal wave expansion technique. After an initial theoretical formulation of the modal wave expansion followed by simulations, it is shown how the limitation of the minimum required number of measurement points in conventional calibration techniques can be eliminated. Experimental results with an antenna array at 150 GHz demonstrate that this novel approach achieves a significant reduction of the number of angular measurement points, especially for large arrays with a high channel count, without degrading the DoA estimation performance.