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.
Laminate presets. Each preset is copied from its manufacturer’s own document for one named construction, and every value is typical, not guaranteed: Shengyi S1141 technical data sheet (2021), a standard-grade FR-4 measured on a 1.6 mm 8×7628 board; Isola 370HR Dk/Df tables, Rev. C (2020), core 1×2116 at 51 % resin; Panasonic MEGTRON 4 R-5725, data sheet 22040132 (2022), 2116 at 56 %; MEGTRON 6 R-5775(N), 22040130 (2022), 2116 at 56 %; MEGTRON 7 R-5785(GE) and (GN), 22040128 (2022), 2116 at 53 % and 55 %; and Rogers RO4350B at its design Dk of 3.66, not the 3.48 process Dk. Dk and Df change with frequency, construction and test method, so the preset reads them at a 10 GHz reference, as this calculator has no frequency input. It interpolates only between points measured by one method, and outside them it uses the nearest tabulated point and says so. Two cores of the same product can differ by more than two products do, so sign off with your fabricator’s stackup values. The sources are rows C-27 to C-33 of the claim ledger.
Related
Sources
- Isola — 370HR Dk/Df tables C-27
- Panasonic — MEGTRON 4 data sheet C-28
- Panasonic — MEGTRON 6 R-5775(N) data sheet C-29
- Panasonic — MEGTRON 7 data sheet C-30
- Rogers — RO4350B laminates C-32
- Shengyi — S1141 technical data sheet C-33
Rows marked with a claim id are tracked in the claim ledger, which records what each source can and cannot establish.