Folded Dipole Antenna Calculator
Calculate dimensions, feed impedance, gain, and matching requirements for a standard folded dipole antenna.
2
Inputs
Live
Math
3
Related
Enter parameters and click Calculate to view results
Formula & Theory
Total Length ≈ (143/f) × VF, Feed Impedance ≈ 300 ΩThis formula is used to calculate antenna parameters for folded dipole antenna calculator.
Overview
The Folded Dipole Antenna Calculator helps RF engineers, amateur radio operators, antenna designers, broadcast engineers, and students design a standard folded dipole antenna for a chosen operating frequency. It calculates wavelength, total antenna length, individual element length, feed-point impedance, estimated antenna gain, recommended mounting height, and balun requirements. Folded dipole antennas are widely used as driven elements in Yagi-Uda antennas, FM broadcast antennas, television receiving antennas, VHF and UHF communication systems, and impedance-matched RF applications.
Input Guide
Enter Frequency, Velocity Factor exactly in the units shown by this folded dipole antenna. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Frequency — use MHz.
- Velocity Factor.
Output Guide
The results describe the calculated folded dipole antenna values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.
How This Calculator Works
The Folded Dipole Antenna uses Total Length ≈ (143/f) × VF, Feed Impedance ≈ 300 Ω. Supply Frequency (MHz), Velocity Factor in the displayed units, then use the calculated values as the first engineering target for this dipole antennas design or analysis.
Design Notes
A folded dipole antenna consists of two parallel conductors connected at both ends, producing a feed-point impedance of approximately 300 Ω when constructed with equal-diameter conductors. Compared with a standard half-wave dipole, the folded dipole offers a wider bandwidth, improved impedance matching, and greater compatibility with balanced transmission lines. The velocity factor affects the physical length required for resonance, while installation height, nearby conductive objects, conductor diameter, and surrounding structures influence the final resonant frequency and radiation pattern. Practical antenna performance may also vary because of feed-line losses, balun quality, environmental conditions, and construction tolerances.
Build and Tuning Notes
Use the calculated dimensions as the starting point when building a folded dipole antenna. Install the antenna at least one-half wavelength above ground whenever practical to improve radiation efficiency and pattern stability. Use a suitable 4:1 balun when connecting a 300 Ω folded dipole to a 75 Ω coaxial feed line, or select an appropriate matching network for other feed systems. After construction, verify resonance and impedance using an antenna analyser or vector network analyser (VNA), then trim the element length gradually if frequency adjustments are required.
Frequently Asked Questions
What is a folded dipole antenna?
A folded dipole antenna is a half-wave dipole consisting of two parallel conductors connected at both ends. It typically has a feed-point impedance of approximately 300 Ω and provides wider bandwidth than a standard half-wave dipole.
Why does a folded dipole have a 300 Ω impedance?
A standard folded dipole made from equal-diameter conductors has a feed-point impedance of approximately 300 Ω, which is about four times the impedance of a conventional half-wave dipole because of its current distribution.
Why is a 4:1 balun recommended?
A 4:1 balun transforms the folded dipole’s approximately 300 Ω balanced impedance to a 75 Ω unbalanced coaxial cable, providing efficient power transfer and reducing common-mode currents.
Where are folded dipole antennas commonly used?
Folded dipole antennas are widely used in FM broadcast antennas, television antennas, VHF and UHF communication systems, amateur radio, base stations, and as the driven element in Yagi-Uda antenna arrays.
How does the velocity factor affect antenna length?
The velocity factor accounts for the electrical properties of the conductor and insulation materials. Lower velocity factors require a slightly shorter physical antenna length to achieve resonance at the desired frequency.
Why can the measured resonant frequency differ from the calculated value?
Actual resonance may vary because of conductor diameter, nearby objects, mounting height, balun characteristics, feed-line effects, environmental conditions, and construction tolerances. Fine-tuning after installation is normally required.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.