A Method of Differences for Determining the Propagation Constant from Multiline Measurements

Abstract

Propagation constant versus frequency curves are obtained after processing S-parameters measured to several lines differing only in length. The proposed method can be easily implemented once the thru-reflect-line (TRL) eigenvalues are calculated considering different combination of line pairs. The noticeable simplicity of the approach when compared to the original multiline algorithm makes it an attractive alternative to improve the determination of the complex propagation constant in practical applications by using experimental data collected to more than two lines. Here, applicability is demonstrated up to 110 GHz for printed circuit board (PCB) microstrip lines. Furthermore, it is provided an improved equation to determine the effective relative permittivity once the complex propagation constant is determined.