A laminar subsidiary resonance limiter

A laminar subsidiary resonance limiter that reduces the threshold power level for limiting by an order of magnitude has been developed. The design was derived from a computer investigation of the effects of ferrite demagnetizing factors on threshold power level for ferromagnetic limiting. Minimum threshold power level is achieved when the demagnetizing factor in the direction of the applied dc biasing field is zero. This occurs only in a needle geometry. Multiple needles are required to have sufficient ferromagnetic material for effective limiting. A laminar design consisting of alternate ferromagnetic and dielectric rods is used to obtain dc magnetic field isolation between the ferrite rods. This design gives the desired dc magnetic field demagnetizing factors while providing a dominant mode propagation path for the microwave signal. An X-band limiter has been developed. It consists of 11 rectangular YIG rods separated by dielectric rods of the same dimensions and mounted on the narrow side of RG-52/U X-band waveguide. A combination of polycrystal and single-crystal YIG rods are used to increase the dynamic range of the limiter. The waveguide structure also effectively eliminates high-loss magnetostatic modes. The limiter has a threshold power of 2 watts and a dynamic range greater than 30 db. The insertion loss is less than 0.5 db over the frequency range of 8.5 to 9.3 GHz. Techniques for further reducing the threshold, utilizing rf magnetic field concentration techniques, will also be described.