The structure is excited with RF by winding a ''primary'' coil around the tall pointy end of the structure. The ''secondary'' is the split-ring at the wide end of the structure.
The structure has the form of a Hyperboloid. Italian physicist and mathematician Evangelista Torricelli called this shape ''Gabriel's Horn''.
It can be thought of as a 3D ''cross - section'' of a shape which exists in more dimensions. See the book ''Flatland'' by Edwin Abbott Abbott for more insight.
1. Impedance Measurements with VNA
2. Frequency Sweep and RF average power measurements
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