Antenna Length Calculator Formula
Understand the math behind the antenna length calculator. Each variable explained with a worked example.
Formulas Used
Full Wavelength
full_wavelength_m = wavelength_mHalf-Wave Dipole
half_wave_cm = wavelength_m / 2 * 100Quarter-Wave Monopole
quarter_wave_cm = wavelength_m / 4 * 100Variables
| Variable | Description | Default |
|---|---|---|
frequency_mhz | Frequency(MHz) | 433 |
wavelength_m | Derived value= 299.792 / frequency_mhz | calculated |
How It Works
Antenna Length
Formulas
Wavelength = c / f = 299.792 / f(MHz) meters
Half-wave dipole = wavelength / 2
Quarter-wave monopole = wavelength / 4
In practice, antennas are shortened 2-5% due to end effects and conductor diameter.
Worked Example
Design an antenna for 433 MHz ISM band.
- 01Wavelength = 299.792 / 433 = 0.6924 m
- 02Half-wave dipole = 0.6924 / 2 = 34.62 cm
- 03Quarter-wave = 0.6924 / 4 = 17.31 cm
Frequently Asked Questions
Why does size matter?
An antenna resonates when its length matches a fraction of the wavelength. Off-resonance antennas have poor efficiency and high VSWR.
What about PCB antennas?
PCB trace antennas are physically shorter due to the substrate dielectric constant. Multiply by velocity factor (typically 0.6-0.8).
Half-wave vs quarter-wave?
Half-wave dipoles are balanced and need a balun. Quarter-wave monopoles need a ground plane but are simpler and half the size.
Ready to run the numbers?
Open Antenna Length Calculator