High-Frequency PCB Design – Does Via Size Matter?

high frequencypcb-design

Here is an image of an LNB and there is some different "Via"s in the PCB that I don't know Why do they use different size of Vias in such circuits. Why? Any reason?

I showed two Vias using two arrows that are close each other(Right side of the image).


Best Answer

enter image description here

Vias have inductance and the more spindly they are, the larger the inductance. Note that in the equation above, inductance is proportional to the height of the via multiplied by the formula in the square brackets. That square bracket formula result is smaller when dimension \$d\$ is larger hence, inductance drops with larger diameter vias.

Picture from this website.

You also can't rule out parallel resonance with its parasitic capacitance either. The inductance and capacitance of the via form a parallel tuned circuit and, that could block a high frequency component of a signal in some cases. Using two different via sizes side-by-side might be the way the designer had in mind of "spoiling" the resonances.