Modeling and Experimental Verification of Time-varying Ferrite-basedMicrostrip Line

We analytically model and experimentally validate a ferrite-based microstrip line subjected to a time-modulated magnetic bias. A ferrite substrate saturated by a permanent-magnet DC bias is additionally exposed to a continuous-wave magnetic field at angular frequency $\Omega$, producing temporal modulation of the bias. This modulation generates sidebands around a propagating microwave tone at $\omega_0$, appearing at $\omega_0+n\Omega$. An adiabatically generalized transmission-coefficient model is developed that incorporates the intrinsic ferrite stopband, predicting both the frequency-dependent insertion loss of the RF carrier and the relative attenuation of the sideband amplitudes. The model’s accuracy—including the stopband effect and sideband-level variation—is experimentally confirmed. Sidebands as high as –34 dBc are observed even though the AC bias component is approximately 330 times weaker than the DC field. Measurements under static and time-varying bias conditions closely match the theory, demonstrating a practical means of inducing time-varying permeability for ferrite-based frequency conversion and temporally engineered nonreciprocal devices.