A near-field setup with independent amplitude and phase control of the stimuli for phased antenna testing

Abstract

This contribution discusses a near-field antenna setup capable of delivering multiple input signals with controllable (i.e., user defined) amplitude and phase relations to an antenna under test, operating in the X-band. The setup is based on a Cartesian modulation (phase and quadrature signals) of phase coherent signals, achieved employing broadband passive IQ-mixers controlled via high-resolution digital-to-analogue converters (DACs). A dedicated calibration procedure allows achieving independent phase and amplitude control on the different signal paths to compensate for loss and delay mismatches among the different channels. The capability to align the relative phases of the various paths with respect to one enables the direct testing of phased antenna arrays. The system calibration is elaborately described. The proposed Cartesian modulation is demonstrated by studying a complex antenna array, with a subset of its elements being controlled independently and phase delayed for actively controlling the far-field radiation pattern.