Analysis of characteristic impedance of strip double line

Characterise impedance is a main parameter of the microwave transmission line; we can calculate the characteristic impedance of the microwave transmission line use quasi-static method, which key is to get the distribution capacitance of the static field. The method most frequently used to calculate distributing capacitance is conformal transformation method. General microwave transmission line like coax, micro-strip line, strip line, parallel double-line etc, and impedance of them can be calculated with conformal transformation method. In this thesis, we calculate the characteristic impedance of strip double line using two times conformal transformation method and mirror theory. The result is same with the result using mirror image law combine micro-strip line characteristic impedance when the ratio of distance and width of double line greater than 0.5. Both methods are effectual