Wavelength and antenna effects calculator
Compute electromagnetic wavelength from frequency with εr or velocity factor correction. Outputs 1/4λ, 1/10λ and 1/20λ critical lengths for antenna design and EMC shielding.
Formulas
λ = c / f (free space)
λ = (c · VF) / f = c / (f·√εr)
VF = 1/√εr
1/4λ resonance · 1/10λ radiation onset · 1/20λ max shielding aperture
Engineering background
A trace, cable or slot approaching 1/4 wavelength becomes an efficient resonant antenna. The 1/20λ rule sizes shielding apertures for roughly 20dB attenuation. Wave speed slows in dielectrics, corrected via εr or VF.
Key benefits
Enter a frequency and instantly get four critical lengths: 1λ, 1/4λ, 1/10λ and 1/20λ.
Supports velocity-factor (VF) or dielectric-constant (εr) correction for free space, PCB traces and coaxial cables.
Directly outputs the maximum shielding aperture (1/20λ) for enclosure design.
How to use
- 1 Enter the frequency and select its unit (Hz/kHz/MHz/GHz).
- 2 For dielectric correction, enter VF or εr and switch modes.
- 3 Read the 1λ, 1/4λ, 1/10λ and 1/20λ results.
Use cases
- › Antenna design: compute half-wave dipole / 1/4λ monopole resonant length.
- › Enclosure shielding: size apertures per the 1/20λ rule.
- › PCB layout: check whether a trace approaches 1/4λ and becomes an unintentional antenna.
FAQ
How do VF and εr relate?
VF = 1/√εr. They are equivalent ways to describe wave-speed reduction in a dielectric; cable vendors use VF, PCB designers use εr.
Why is 1/4λ a dangerous length?
At 1/4λ an open-ended trace presents very low source impedance, draws maximum current and radiates efficiently, becoming an unintentional antenna.
How much shielding does the 1/20λ rule provide?
Roughly 20dB. Keeping apertures below 1/20λ reduces RF leakage to an acceptable level.