Broadband Determination of the Even- and Odd-Mode Propagation Constants of Coupled Lines Based on Two-Port Measurements

Abstract

We describe a method for the broadband measurement of the even- and odd-mode propagation constants of symmetrical coupled transmission lines. The main advantage of the method, its simplicity, lies in the lack of need for four-port measurements. Only two-port measurements are required, and thus just a two-port vector network analyzer (VNA). The accuracy of the results can be increased at the cost of a higher number of measured coupled-line lengths. The new approach has been successfully applied for the determination of coupled microstrip lines in the 2- to 20-GHz frequency band in both simulated and experimental cases. A brief discussion about the repeatability of the microstrip launcher and the adverse effects of radiation is included.