Characterization of Phased Arrays Using Amplitude-Modulated Interferometry

This article presents amplitude-modulated interferometry (AMI) as an approach for parallel testing and calibration of phased arrays. In AMI, each array element’s response is orthogonally modulated and aggregated, and the aggregate is squared using a noncoherent power detector. The resulting low-frequency cross-correlations are demodulated using the appropriate code products. These correlations are used to estimate each element’s gain and relative phase. Compared with the prior phase-modulated interferometry (PMI) approach, where each element’s phase is modulated, AMI uses amplitude-shift keying to modulate each element’s amplitude using variable-gain amplifiers, attenuators, and/or vector interpolators. Amplitude modulation (AM) circumvents the inherent phase imbalance problem in PMI, in which phase modulation (PM) error corrupts the extracted results and must, therefore, be de-embedded using additional measurements. We present a theory for AMI and a technique for de-embedding its nonidealities. We validate our methods using measurements of an 8-GHz eight-element array. Finally, we compare AMI to PMI and vector network analyzer (VNA) measurements using a 28-GHz, 64-element phased array. Despite the array’s PM errors, AMI accurately extracts amplitude and phase with root-mean-squared errors (RMSEs) of 0.1 dB and 1.0°. AMI outperforms PMI in accuracy and speed and achieves state-of-the-art results for phased-array testing.