Analysis of a high power ferrite differential phase shift circulator operating above ferrimagnetic resonance

Magnetic losses limit the power handling/frequency performance of all ferrite phase shift and control components. At high power levels nonlinear loss is prevalent but this can be avoided using a technique called ‘mode segregation’. It is noted that this is achieved by biasing the ferrite above ferrimagnetic resonance. A combined magnetostatic/microwave finite element scheme is used to model this mode of operation in a differential phase shift structure used in air traffic control surveillance radars. Starting from the nonlinear material magnetisation curve, the magnetic state of the ferrite is evaluated as a prerequisite to calculating the full microwave solution. Above resonance operation avoids nonlinear loss but this study indicates that the differential phase shift is reduced and larger magnetic bias fields are required. Calculations agree well with the experimental data.