Mutual Coupling in Compact Orthomode Transducers

The scattering parameters of generalized compact orthomode transducers using azimuthally-distributed field probes in a dual-mode waveguide are analyzed. Theoretical expressions constraining the mutual coupling between the probes are derived and evaluated for three- and four-probe orthomode transducers with and without a coaxial reference port for calibration injection. The mutual coupling is shown to be identically zero or cancel coherently in all cases, suggesting that radiometric receivers with the best possible system noise temperature may be realized using these topologies.