How do vias and grounding affect RF circuits?
At RF, a ground via is an inductor, roughly a few tenths of a nanohenry to about 1 nH depending on length and diameter, so a single via at 5 GHz can present tens of ohms. Multiple vias in parallel, short via lengths (thin dielectrics) and placing vias right at component pads reduce ground impedance. Rows of vias (stitching and fences) tie ground pours together and suppress parallel-plate modes and coupling.[1][2]
How much inductance does a via have?
A widely used approximation for a via of height h and diameter d (both in mm) is L ≈ 0.2·h·[ln(4h/d) + 1] nH. A 1.6 mm via with 0.3 mm diameter is about 1.3 nH; a 0.2 mm via to a nearby ground layer is far less. At 2.4 GHz, 1.3 nH is about 20 Ω of reactance.[1]
Why does return path matter?
High-frequency return current flows on the reference plane directly beneath the signal trace, confined to a few trace heights. A signal changing reference layers needs a nearby ground (or decoupled supply) via so the return can follow; otherwise the return detours, increasing loop inductance and radiation.[2]
How should vias be placed?
- Two or more vias at each ground pad of RF ICs and shunt components.
- Thermal pads of RF ICs and PAs filled with a via array for both ground and heat.
- Via fences along CPW and between sections, spaced less than λ/10 (λ/20 common).
- Ground vias next to every signal via in layer transitions.
Frequently asked questions
Is ground really zero volts at RF?
No; ground conductors have inductance and voltage drops.
Why use many small vias?
Parallel vias reduce inductance and improve heat transfer.
What is a via stub?
The unused portion of a through via beyond the signal layer, which resonates at high frequencies.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Signal and Power Integrity, Simplified, 3rd ed.”. E. Bogatin, Prentice Hall. 2018.
- “Electromagnetic Compatibility Engineering”. H. W. Ott, Wiley. 2009.