A simple closed-form equation for shunt capacitances at a gap structure in the center conductor of a coaxial line

摘要

In this report, a simple closed-form equation for shunt capacitances at a gap structure in the center conductor of a coaxial line is presented. This equation is derived on the assumption that value of the shunt capacitance is in proportion to amount of energy in half volume of the above gap structure that is stored by evanescent modes at a gap structure with infinitely large interval between center conductors. In order to simplify the equation, in procedure of derivation, set of the evanescent modes has been approximately represented by TM01 mode of circular waveguide, which has cross-sectional field pattern similar to that of TEM mode of coaxial line. Values of capacitance calculated from proposed equation have good agreements with those evaluated from finite element method. Especially, proposed equation gives accurate results in case that diameter of center conductor is comparatively large.