A New Approach to YIG-Based Band-Reject Filters: An Introduction

Staples of many microwave block diagrams, oscillators and filters rely on resonant behavior to function. At higher frequencies, it is often the physical size of the item being leveraged that dictates the frequency of resonance, the size of the crystal, the size of the cavity, as examples. Yttrium iron garnet (YIG) has an unusual property, in that its resonant properties do not depend directly on size, but instead on the strength of magnetic field passing through it. This has some downsides, but also some major benefits, as we’ll see. Common functions provided by YIG resonators include oscillators, band pass filters, and band reject filters. This paper focuses on the latter, but many of the principles discussed apply to all.