Complex propagation in a novel ferrite-filled rectangular waveguide isolator

This paper investigates the propagation constant of a novel rectangular waveguide ferrite isolator. For the first time, losses associated with the device are considered. The field solution of the isolator´s forward propagating mode is derived and includes dielectric loss, ferrite linewidth, and conductor loss. Roots of the propagation constant´s transcendental equation are then sought on the complex plane using a gradient descent method. The impact of the losses on the isolator´s performance is then assessed. Given practical loss values of tan delta = 3(10^-4), DeltaH = 250 Oe and sigma_cu = 5.813(10⁷) S/m, an isolator having a waveguide width of only 6 mm will produce a forward attenuation of less than 0.051 dB/cm at 4.1 GHz, resulting in an isolator figure of merit of 89.5 dB.