How are wavelength and frequency related?
Wavelength is λ = v/f, where v is the propagation velocity. In free space v = c ≈ 2.998×108 m/s, so λ(m) ≈ 300/f(MHz): 1 GHz corresponds to about 30 cm. In a medium with relative permittivity εr, the velocity is c/√εr, shortening the wavelength.[1]
What is velocity factor?
Velocity factor VF = v/c = 1/√εeff. Solid-polyethylene coax has εr ≈ 2.25 and VF ≈ 0.66; foam dielectrics reach about 0.8–0.85. On microstrip the field is partly in air, so the effective permittivity lies between 1 and εr.[1]
What is electrical length?
Electrical length is physical length expressed in wavelengths or degrees: θ = βℓ = 2πℓ/λg. A quarter-wave line is 90°. Electrical length, not physical length, determines transformer and stub behavior, and it varies with frequency, which is why distributed networks are band-limited.
When does a circuit stop being lumped?
Lumped analysis assumes negligible phase change across the circuit. A common rule of thumb is that structures shorter than λ/10 (some designers use λ/20) can be treated as lumped.[1] For digital edges, the relevant frequency is set by rise time (bandwidth ≈ 0.35/tr).[2]
What are some reference wavelengths?
| Frequency | Free-space λ |
|---|---|
| 10 MHz | 30 m |
| 100 MHz | 3 m |
| 915 MHz | 32.8 cm |
| 2.45 GHz | 12.2 cm |
| 5.8 GHz | 5.2 cm |
| 28 GHz | 10.7 mm |
| 77 GHz | 3.9 mm |
Frequently asked questions
What is the wavelength at 2.4 GHz?
About 12.5 cm in free space.
Why is guided wavelength shorter?
Waves travel slower in a dielectric, by a factor of 1/√ε_eff.
What is a quarter-wave at 1 GHz in air?
About 7.5 cm.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Microwave Engineering, 4th ed.”. D. M. Pozar, Wiley. 2012.
- “Signal and Power Integrity, Simplified, 3rd ed.”. E. Bogatin, Prentice Hall. 2018.