Wavelength
Wavelength is propagation velocity divided by frequency.
λ = v ÷ f
In free space, 100 MHz has a wavelength near 3 m. In cable or dielectric material, velocity factor reduces propagation speed and wavelength.
Antenna Element Length
A quarter-wave element starts near λ/4, but physical antennas are commonly shortened by end effects, conductor diameter, insulation, surroundings, and the selected velocity factor.
Lquarter = VF × λ ÷ 4
Calculated length is a starting point. Final tuning depends on the installed environment and measured impedance or standing-wave ratio.
Skin Depth
Skin depth is the distance where current density falls to about 36.8% of its surface value in a good conductor.
δ = √[2 ÷ (ωμσ)]
Higher frequency, permeability, or conductivity reduces skin depth. Current still exists below one skin depth; it decays exponentially rather than stopping at a hard boundary.
Practical Limits
Surface roughness, plating thickness, conductor geometry, proximity effect, magnetic materials, temperature, and frequency-dependent material data can all change loss.
Use field-solvers, measured material properties, or transmission-line models when conductor loss is design-critical.