Amplitude-Only Measurement Method of Complex Transmission Matrix for Multibeam Pattern Testing of Phased Array Antennas

Multibeam pattern testing of phased array antenna under test (AUT) plays a crucial role in its beam-steering capability evaluation. Instead of measuring multiple steered beams sequentially in a time-consuming way, some fast multibeam test methods were presented in the literature by the synthesis of complex element patterns measured. However, the complex measurement of array element patterns is challenged by the integrated design of phased arrays and the susceptible phase measurement at millimeter-wave and terahertz frequencies. To address this issue, this article proposes an amplitude-only measurement method of a complex transmission matrix in a near-field setup. The rotating-element electric-field vector (REV) measurement is first conducted on the probe array side to obtain the relative transmission coefficients from AUT array to multiple probe branches. With one probe branch enabled each time, REV measurement is then conducted on AUT array side to obtain the relative transmission coefficients from multiple AUT element branches to a single probe branch. By combining the relative relationships above, the complex transmission matrix between AUT elements and probes is obtained, which is required to reconstruct the complex element patterns for multibeam pattern test of phased arrays. Besides, this article addresses the ambiguity issue of REV solutions by the postprocessing calculation on the original REV measurement data, without extra dedicated measurements for the solution distinction. In experimental validation, the complex transmission matrix measured by the proposed amplitude-only method is matched well with the reference complex measurement results, with a phase error within ±4°.