A simple, low-cost yet efficient polarization sensing system, capable of determining the polarization state of a self-oscillating circularly-polarized active integrated antenna (CPAIA), is proposed and demonstrated. The newly developed sensing system is capable of retrieving the phase difference information between the orthogonal field components of a CPAIA without the need of a common synchronous reference signal as that in a conventional pattern measuring system. The two orthogonal electrical fields are captured and mixed to retrieve the relative phase difference information as dc voltages. As a proof of concept, the polarization sensing system has been successfully developed on a printed circuit board, while a typical passive circularly-polarized antenna and a self-oscillating CPAIA were fabricated as a pair of antennas under test (AUTs). On one hand, the passive AUT characterized by the sensing system was supported by data from a commercial measuring setup to validating the accuracy of the newly developed system. On the other hand, the proposed sensing system is believed to be the first demonstration dedicated to retrieving the polarization information of a self-oscillating CPAIA, and hence pave a new way to fully characterize this special sort of active antennas.
