Antenna Frequency Calculator
Convert between frequency and wavelength. Calculate quarter-wave and half-wave antenna lengths.
Common frequency bands reference
What is an antenna frequency calculator?
An antenna frequency calculator determines the optimal antenna dimensions for a specific frequency or identifies which frequency a given antenna is tuned to. The fundamental relationship is that an antenna's physical length is directly related to the wavelength of the radio frequency it transmits or receives. A half-wave dipole antenna, for example, is approximately half the wavelength of its target frequency.
This tool calculates antenna length for common antenna types (dipole, quarter-wave, Yagi, J-pole) across frequency ranges from HF radio to microwave. It helps amateur radio operators, SDR enthusiasts, and wireless engineers design antennas for specific bands without manual wavelength calculations.
How to use this tool
Enter a frequency in MHz (or select from common bands like FM radio, ham radio, Wi-Fi, cellular). Choose the antenna type. The tool calculates the optimal physical dimensions in both metric and imperial units. It also shows the wavelength, the velocity factor for common transmission line types, and adjustment notes for real-world conditions.
Common antenna types
- Half-wave dipole — the most fundamental antenna. Length = wavelength / 2. Omnidirectional radiation pattern.
- Quarter-wave ground plane — half a dipole with a ground plane. Common for VHF/UHF. Length = wavelength / 4.
- Yagi-Uda — directional antenna with multiple elements. Used for TV reception and point-to-point communication.
- J-pole — a half-wave antenna fed at the bottom through a quarter-wave matching section. Easy to build and effective.
The frequency-wavelength relationship
Wavelength (meters) = speed of light / frequency. Since the speed of light is approximately 300,000,000 meters per second: wavelength (m) = 300 / frequency (MHz). A 100 MHz FM radio signal has a wavelength of 3 meters, so a half-wave dipole for FM radio is about 1.5 meters long. Higher frequencies have shorter wavelengths and require smaller antennas.
Frequently asked questions
Why are real antennas slightly shorter than the calculated length?
The speed of electromagnetic waves along a conductor is slightly less than the speed of light in free space (typically 95% for wire antennas). This velocity factor means antennas are about 5% shorter than the pure wavelength calculation suggests. Antenna diameter, nearby objects, and height above ground also affect the optimal length. Most builders start with the calculated length and trim to tune.
What is antenna resonance?
An antenna is resonant at a frequency where its impedance is purely resistive (no reactive component), meaning it efficiently converts electrical energy to radio waves. A half-wave dipole has a resonant impedance of about 73 ohms. Off-resonance, the antenna still works but less efficiently — some energy is reflected back. Resonant antennas are the most efficient, which is why precise length calculations matter.