In this report, some problems of initial phases determination of PAA channels (PAA calibration) are considered. These problems usually arise during in-service re-calibration of PAAs, when it is not possible to provide a measurement environment which are close to laboratory environment. Specific challenges that occur during multi-element PAA calibration procedures are taken into account.

Calibration errors because of inaccurate calibration probe positioning are considered. Influences of signal reflections from environment objects on calibration results are examined. Effects of signal power measurement errors on calibration quality are estimated. Method of normalization to common reference point (initial phases “staple” method) for initial phases when multi-element PAA part-by-part calibration, is offered.