Semi-Analytical Modeling of Coaxial Feeds

A highly accurate semi-analytical model is given for the widely used practical topology of a coaxial feed exciting an arbitrary grounded planar structure. The probe connecting the inner conductor of the coaxial topology to the planar structure may cross an arbitrary number of layers. The core of the model is the comparison of the actual configuration with a parallel plate system, which can be studied quasi-analytically. It is shown that most of the modal fields found in the parallel plate system can be transferred to the actual configuration without modification. This allows to build a highly accurate model, without having to compromise calculation times. It is shown that in practical single and double layered cases, the model reduces to adding a capacitor in parallel. It is thus extremely easy to incorporate in existing modeling tools.