Full Characterization of Circularly Polarized Orthomode Transducers Using Short-Circuit Termination

A straightforward retrieval algorithm for the circularly polarized (CP) orthomode transducer (OMT) scattering matrix is proposed, utilizing three offsets short-circuited Common Port terminations. Leveraging equivalent voltage theory, a detailed, systematic mathematical analysis is presented to characterize the impedance matching of all ports, isolation, transmission, co-polarization, and cross-polarization without requiring the back-to-back (BTB) configuration or additional load terminations. Moreover, the scattering matrix of dissimilar BTB OMTs is predicted by fully identifying a single CP OMT. All mathematical analyses are first validated through full-wave simulations of various CP OMTs, thereby obviating the uncertainties introduced by fabrication tolerances. Experimental validation using a novel OMT with an irregular hexagonal cross section also assures the algorithm’s robustness and broad applicability. The retrieved phase constant shows strong agreement due to minimal fabrication tolerances in the Common Port opening, while the retrieved scattering parameters exhibit satisfactory agreement with minor deviations influenced by fine structural dimensions. Therefore, the proposed analysis establishes a robust, low-cost framework using only a standard two-port vector network analyzer (VNA), offering key advantages over existing far-field and BTB approaches.