Closed-Form Expressions for the Current or Charge Distribution on Parallel Strips or Microstrip

Simple but accurate closed-form expressions for the charge and current distributions on parallel-plate stripline or microstrip are given. This form is convenient for use in various applications, such as determining radiation or mode fields of the lines, or frequency dispersion of the fundamental mode of the microstrip. These expressions are used to obtain explicit expressions for the capactitance of these lines, accurate to within one percent of the actual value for any ratio of stripwidth to spacing.