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(10 7 ) 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.