Frequency-dependent characteristics of microstrip transmission lines

This dissertation is concerned with the studies on the frequency-dependent characteristics of microstrip line structures. Relevant considerations are applied to evaluate crosstalk in symmetric, coupled and lossy (dispersive) microstrip transmission lines. The technique adopted supplements the wide-range of semi-empirical expressions available in the literature on the frequency-dependent even- and odd-mode effective dielectric constants as well as the characteristic impedances of coupled microstrip lines. The accuracy of a crosstalk transfer function deduced is verified with theoretical and experimental results. The behavior of crosstalk versus line-spacing, dielectric substrate characteristics, and line-length is analyzed. This study is also extended to address the influence of temperature on crosstalk induced in microstrip lines. Further, analogous to relaxation considerations of Cole-Cole diagrams as applied to dielectric materials, a "reactive relaxation" concept is introduced to represent the frequency-dependent characteristics of lossless and lossy microstrips. The present algorithm depicting the dynamic permittivity of the microstrip structure (via Cole-Cole diagram) directly leads to a convenient and modified Smith chart representation. It includes the frequency-dependent influence of the fringing field and the lossy characteristics cohesively. Results based on the proposed model are compared with the available data in the literature in respect of a microstrip patch antenna. As far as the authors know of, this is the first attempt in depicting the dispersion characteristics of a microstrip line via Cole-Cole diagram format.