Computer-Aided Analysis of Dissipation Losses in Isolated and Coupled Transmission Lines for Microwave and Millimeter-Wave Integrated-Circuit Applications
NAVAL RESEARCH LAB WASHINGTON DC
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The analysis employs a quasi-TEM model for uniform isolated transmission lines and for the even- and odd-mode transmission lines associated with coupled-line structures. The conductor and dielectric losses in these structures are then related to equivalent charge-density distributions, which are evaluated using a method-of-moments solution. The transmission lines treated by this which are evaluated using a method-of-moments solution. The transmission lines treated by this analysis may contain any number of lossy conductors and inhomogeneous dielectrics, consisting of any number of different homogeneous dielectric regions. After explicit expressions are developed for use in evaluating conductor and dielectric loss coefficients for the even and odd modes of coupled transmission lines a development is provided to explicity relate the four-port, terminal, electrical performance of directional couplers to the modal loss coefficients. Losses are evaluated for examples of four isolated transmission lines and one coupled transmission line. For microstrip and coplanar waveguide the computed loss coefficients are in reasonable agreement with experimental data. For inverted microstrip and trapped inverted microstrip, evaluations presented in both tables and graphs provide useful design information for circuit applications. A comparison is made of the total loss characteristics of microstrip, coplanar waveguide, inverted microstrip, and trapped inverted microstrip. The utility of the analysis for coupled- transmission-line losses is illustrated for the example of edge-coupled microstrip with a dielectric overlay by comparing computed loss characteristics with measured values.
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