Fabry–Perot Open Resonator Technique for Dielectric Permittivity and Loss Tangent Measurements of Yttrium Iron Garnet

This paper presents a Fabry-Perot open resonator system for the precision measurement of real part of permittivity and loss tangent of yttrium iron garnet specimens at 60 GHz. This system allows us to vary the cavity length at 10-nm step size to study the resonance profile of each excited fundamental mode with great stability and reproducibility. The obtained highly symmetrical, fully resolved Gaussian resonance profile results in a significantly high Q factor for the overall system. It enables us to determine the dielectric permittivity and loss tangent of ferrite materials accurately and reliably for the first time. Measurements have been performed on a 99.9% pure yttrium iron garnet and a gadolinium substituted yttrium iron garnet specimen at 60 GHz. A temperature dependence study has also been conducted at a limited temperature range near room temperature

I. Introduction

Ferrites materials such as yttrium iron garnet (Y₃ Fe₅ O₁₂, YIG) have been extensively used in the burgeoning microwave/millimeter wave and telecommunication industries for decades. YIG possesses the highest quality factor in the microwave regime and the narrowest linewidth in magnetic resonance among the magnetic materials. It is a good candidate for microwave and millimeter wave circulators, oscillators, phase shifter, and other narrow band devices. As a result, a precise understanding of the dielectric properties of YIG and its derived compounds at microwave/millimeter frequencies becomes more and more crucial to both designers and manufacturers.