Calculators / 10
Power Plane Cavity Resonance Calculator
Two parallel planes are a cavity. When a plane's length is a whole number of half wavelengths, a standing wave builds up between its edges and the plane pair's impedance peaks. Those peaks are where power-plane noise and edge radiation concentrate — and where decoupling has the hardest job.
Reading the numbers
- The first mode comes from the longer side. Its frequency halves when the plane doubles in length.
- A square board has pairs of modes at the same frequency, (1,0) with (0,1), and those coincident modes stack up.
- Decoupling capacitors and vias move every mode; treat these as the bare-board frequencies to design against.
Every value is in the address bar as you change it, so a link reproduces the calculation exactly.
Type values with SI prefixes — 100n, 2.2p, 16G — or
drag the sliders; a bare number keeps the prefix already shown.
The formulas
Go deeper — assumptions, how it is checked, and sources
Assumptions. A bare rectangular cavity with open edges. Fringing at the edges lowers every mode slightly; the planes' own loss, and any capacitors or vias across them, damp the peaks and shift them. The cavity is thin compared with a wavelength, so only the in-plane modes exist.
How it is checked. An air-filled 150 mm plane has its first mode at exactly c/2a; a square plane has (1,0) and (0,1) at the same frequency and (1,1) at √2 times it; and (2,0) is exactly twice (1,0).
Source. G.-T. Lei, R. W. Techentin and B. K. Gilbert, “High-frequency characterization of power/ground-plane structures,” IEEE Trans. Microwave Theory Tech., vol. 47, no. 5, 1999.