diodo impedance
Diodes are very simple things, but hard to measure. That is because they change their characteristics dramatically depending on the RF input power and load impedance on them.
If you just try to measure a schottky diode mounted in-shunt, with a standard network analyzer, you would probably see that it looks like a pure 0.1 pF capacitor. If you instead used a high power network analyzer, so that the diode was rectifying the RF incident on it into DC current, and there was a DC load connected through it via a bias network, you would see something that looked more like a larger capacitor in series with 30-200 ohm resistance. But even that would be a suspect impedance measurement, since if you then designed and added a matching network in front of the diode, its operating point will change again, and give you a different result.