A tunable microwave circulator based on a magnetized plasma as an active gyrotropic element

We present a theoretical analysis and experimental demonstration of a microwave circulator that uses a magnetized plasma as the gyrotropic element. Unlike traditional circulators that exploit the anisotropic permeability of ferrite, here, we exploit the anisotropic dielectric constant of a magnetized plasma to achieve non-reciprocity. The advantage of a plasma-loaded circulator is that it allows for tunability, and modulation that is limited in speed by the ionization/recombination time of the plasma. The theoretical analysis treats the problem of electromagnetic scattering from a heterogeneous gyrotropic plasma rod to confirm scattering behavior and to guide in defining the design parameter space covered by more detailed computational simulations. Proof-of-concept experiments are carried out using a custom-fabricated low-frequency gas discharge tube as the plasma element. Here, we confirm the plasma-frequency dependent tunability predicted by the simulations, demonstrating this tunability in the experiments by varying the applied discharge voltage. These initial experiments suggest that isolation in excess of 25 dB is achievable, in reasonable agreement with the theory and simulations for studies in the S and C ranges of the microwave spectrum.