Wideband circulator adjustment using the n = ±1 and n = 0 electromagnetic-field patterns

In its matched condition the scattering-matrix eigenvalues of the 3-port junction circulator lie equally spaced on a unit circle. As the frequency is varied, these eigenvalues rotate in the complex plane at different speeds, and the phase relation between them no longer corresponds to an ideal circulator. This is primarily due to the fact that the reference eigenvalue is normally associated with a nonresonant field pattern and the other two eigenvalues are associated with resonant ones. The purpose of the letter is to describe a new adjustment procedure in which the reference eigenvalue is associated with a resonant field pattern also. If the Q factors of all three field patterns are made the same, the three eigenvalues will all rotate at the same speed, around the unit circle. The bandwidth of the circulator will then be very wide.