CAPACITANCE OF A STRIP CAPACITOR

In basic electrostatics, the capacitance of a long rectangular parallel-plate capacitor is formulated, assuming that the aspect ratio (the ratio of the plate separation to the width of capacitor) is very small. In this case, the fringe field of the edges can be neglected. However, the edge effect becomes important for highly precise measurements of dielectric constant and for calculating the capacitance of LSI and microstrip lines whose aspect ratio is not small. The boundary element method (BEM) is a very efficient method for calculating capacitances. Here by using the techniques of BEM, the capacitance of a strip capacitor which includes the edge effect is computed, and a new empirical formula is derived for the capacitance. The new empirical formula can be applied to the capacitance of microstrip lines by using a method of electric images. The capacitance values of microstrip lines calculated by the new formula agree well with results of other analytical expressions and with measured data. © 1990 IEEE