Results of experimental research on a relativistic S-band magnetron with a ferroelectric plasma source as a cathode are presented. The cathode plasma was generated using a driving pulse (∼3 kV, 200 ns) applied to the ferroelectric cathode electrodes via inductive decoupling prior to the beginning of an accelerating pulse (200 kV, 150 ns) delivered by a linear induction accelerator. The magnetron and generated microwave radiation parameters obtained for the ferroelectric plasma cathode and the explosive emission plasma were compared. It was shown that the application of the ferroelectric plasma cathode allows one to avoid a time delay in the appearance of the electron emission to achieve a better matching between the magnetron and linear induction accelerator impedances and to increase significantly (∼30%) the duration of the microwave pulse with an ∼10% increase in the microwave power. The latter results in the microwave radiation generation being 30% more efficient than when the explosive emission cathode is used, where efficiency does not exceed 20%.