Analysis of Error Due to Exclusion of Higher Modes on Complex Permittivity Measurement Using Waveguide with Flange

Abstract

SUMMARY In this letter, we discuss the measurement error due to theexclusion of the higher modes when a waveguide with a flange is insertedwith lossy dielectric material. The reflection coefficient is calculated by aspectrum-domain approach (SDA), which uses only the dominant (TE 10 )mode to realize a simplified nondestructive measurement of complex per-mittivity of lossy dielectric sheets. The analysis shows that the error dueto the exclusion of the higher modes decreases as complex permittivity in-creases. Consequently, we have confirmed that a simplified measurementof complex permittivity is possible by a coverage limitation with the SDA,which excludes the higher modes. key words: measurement of complex pemittivity, rectangular waveguidewith flange, FDTD, SDA 1. Introduction Complex permittivity of medium and high-loss materialshas frequently been measured by the waveguide method [1],[2]. In this method, it is necessary to vary the material struc-ture in order to insert it inside the waveguide so that there isno space left between them. Therefore, the dimension of thesample significantly influences the accuracy of the measure-ment [3]. On the other hand, a method for estimating ma-terial thickness using a rectangular waveguide with a flangehas been presented by a spectrum-domain approach(SDA)[4], which uses only the dominant (TE