The efficiency of a ferrite as a microwave mixer

A method proposed by the Services Electronics Research Laboratory is analysed in detail, and expressions are derived for the efficiency under a variety of conditions. It is shown that, subject to reasonable limitations on the intermediate-frequency spacing, a polycrystalline ferrite should behave in many ways like a single crystal sample and that the S.E.R.L. measurements on magnetization can be explained by assuming a basic line width of a few gauss and a spread in resonant fields from point to point in heterogeneous samples. Owing to a remarkable property of the structure of the formulae, this spread in resonance does not degrade the effective permeability, although the measured value is reduced by a factor of about a hundred. On the figures presented, the tentative conclusion is reached that the conversion efficiency is some 14 dB worse than acceptable conventional crystals will give, although the figures may be capable of improvement. No calculations are made on noise figure.