The behaviour of an open circuit as shown in fig. 12.3 is very similar to that in a microstrip line; that is, the open circuit is capacitive in nature.
A very simple approximation for the equivalent length extension associated with the fringing fields has been given by K.Beilenhoff .
For the open end, the value of is not influenced significantly by the metalization thickness and the gap width when . Also, the effect of frequency and aspect ration is relatively weak. The above approximation is valid for .
The open end capacitance can be written in terms of the capacitance per unit length and the wave resistance.