We simulated microwave far-field radiation by using a coaxial cable, inside which a ferrite layer with a ground plane was loaded. The ferrite layer is magnetically biased near ferrimagnetic resonance by a permanent magnet generating a global bias magnetic field inside the ferrite layer. In addition, a magnetic bias coil near the ferrite layer generates a second dc bias magnetic field so as to locally tune the permeability of the ferrite layer. By observing the frequency change in the resonant modes of the cavity formed by the coaxial cable, we can determine the permeability of the ferrite layer. Calculations compare nicely with experiments.