Effect of parasitics in tunable X-band metamaterial isolators

In this paper the investigations of the parasitics in a fabricated X-band tuneable metamaterial isolator are presented. The isolator applies a microstrip left handed artificial transmission line (LHTL) with Butterworth phase response on an anisotropic ferrite substrate material. The structure is simplified and optimized to reduce the harmful right handed and coupled parasitic effects to achieve stable, spurious resonance free phase characteristic in the targeted 8-12 GHz frequency band. This is required to archive the tuneable 20 dB isolation by varying the applied magnetic field. Detailed analysis shows that both the capacitive and inductive coupling between the consecutive stage printed inductors have no significant effect in realistic structures. Also, the parallel shunt parasitic capacitance can be reduced enough with proper design to have very little effect. The main limiting factor is the series parasitic inductance of both the traces and the applied series capacitors.