Magnetically tunable microwave resonator/filter

Abstract: The magnetic tunability of ferrites has been studied and applied on many electric components for working in various frequency bands. Filters or resonators loaded by ferrites can thus work for different frequency requirements by tunning external biasing field. However, filters or resonators built by traditional waveguides are large in size. And for tunning with biasing field below the ferroresonance point, dissipation in ferrites will increase rapidly if the working frequency is near the ferroresonance zone. It leads to the drop of Q values of resonators and the tuning range is limited to stay away from ferroresonance. For the filter, remaining high Q values in wide frequency tuning range is the base of good performance and tunability. In industry, demands of cost reduction and integration encourage the miniaturization of electric components. It is always challenging but attractive to find solutions compromising size, performance, and implement ability. In this project, investigation for possible solutions of magnetic bias tunable filter is made and their comparisons are presented. Analysis and simulation are made to a specific ferrites-loaded substrate integrated waveguide resonator. With homogeneous below-resonance biased field, results in the reference are reached again and analyzed. With biasing filed above the ferroresonance, higher Q values and smaller size can be achieved and the drop of Q is avoided. A magnet structure is designed to study how the resonator works in inhomogeneous biasing filed. Biasing of below-resonance field is achieved with the magnets structure, though the performance is not good as homogeneous biasing case. A 3-order filter is then built based on the resonator working in the below-resonance bias. It’s a band-pass filter and tunable. A magnet structure is also built and simulated for the filter to verify its feasibility.