Approximate Formulas for Line Capacitance and Characteristic Impedance of Microstrip Line

Soon Yun Poh, Weng Cho Chew, Jin Au Kong

Research output: Contribution to journalArticlepeer-review


A numerically efficient and accurate method for the derivation of line capacitance and characteristic impedance of a thin microstrip line is discussed. Galerkin’s method is found to give highly accurate results when only one or two basis functions are used. We use three methods to derive approximate formulas for microstrip line capacitance and characteristic impedance. Asymptotic lower bounds derived through the variational method and matched asymptotic expansion methods give expressions which reveal the functional forms of these approximate formulas. Seminumerical approximation gives rise to formulas usable on a desk calculator. It is found that there is excellent agreement between the seminumerical formulas, the asymptotic formula derived through matched asymptotic expansions and numerically derived results.

Original languageEnglish (US)
Pages (from-to)135-142
Number of pages8
JournalIEEE Transactions on Microwave Theory and Techniques
Issue number2
StatePublished - Feb 1981
Externally publishedYes

ASJC Scopus subject areas

  • Radiation
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


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