Nonlinearity of microwave ferrite media

Abstract

Existing theories of propagation in magnetized ferrite media predict propagation constants which are independent of the rf field strength only if a number of restrictive conditions are satisfied. In general, however, the propagation constants are functions of the rf field strength and nonlinear propagation is to be expected. One of the conditions for linearity is that the rf magnetic field intensity be small compared to the static magnetizing field intensity. This condition can be violated when the peak power level of the wave incident on the ferrite medium is sufficiently high and indeed, it has been observed by the authors that ferrite loaded waveguides can become nonlinear at peak power levels as low as 1 kw. Results are presented of a study of the behavior of ferrite loaded waveguides at 9,400 mc over input peak power levels from 0.1 kw to 100 kw which includes power levels commonly encountered in radar applications. The dependence upon input power level of the ferrite losses, phase shift, and rotation of the plane of polarization is described for a number of ferrite materials. The effect upon the degree of nonlinearity of the intensity of the static magnetizing field is discussed as well as the dependence upon the dimensions of the ferrite.