Comparison of transmission of coaxial nonuniform transmission lines between electromagnetic fields simulation and circuit simulation

The three-dimensional electromagnetic fields simulation of nonuniform transmission lines that were under consideration for the next generation of Z-pinch drivers was performed by a code called CST microwave studio. A coaxial exponential line model was established in which the inside radius of the outer conductor is 100 mm, the characteristic impedance is 0.203 Ω at the input port and 2.16 Ω at the output port and the input voltage is half-sine pulse wave as TEM mode with an angular frequency of 14 × 10⁶ rad/s. A little energy of non-TEM mode is found during the transmission process. The more severely the radius of the line changes, the more energy of non-TEM mode is found. If the length of the transmission line is long enough, the difference of voltage transmission efficiency between electromagnetic fields and circuit simulation will be less than 1%. In this situation, results of electromagnetic fields simulation can be replaced by circuit situation. (authors)