Free 3-Element Yagi-Uda Antenna Calculator
Calculate precise reflector, driven element, and director element cut lengths, boom spacing, forward gain (dBi), and front-to-back ratio for VHF and UHF beams.
📡 Frequency & Element Tubing
Front-to-Back Ratio: ~18.5 dB • Beamwidth: ~66°
• Reflector to Driven Element: 41.6 cm (0.20 λ)
• Driven Element to Director: 37.4 cm (0.18 λ)
• Total Minimum Boom Length: 79.0 cm (31.1 inches)
Natural Feedpoint Impedance: Adding parasitic elements drops the radiation resistance of the driven dipole from 73 Ω down to approximately 20 Ω to 28 Ω. A Gamma match, hairpin match, or folded dipole is required to achieve a clean 1.1:1 SWR match to 50 Ω coax.
Recommended Tools & Equipment
Tested hardware and components for high reliability
How the Yagi-Uda Antenna Works
Invented in 1926 by Shintaro Uda and Hidetsugu Yagi, the Yagi-Uda antenna uses parasitic elements to shape an omnidirectional dipole radiation pattern into a focused, high-gain directional beam:
- Reflector (Rear): Cut approximately 5% longer than resonant half-wavelength ($0.495 lambda$ to $0.505 lambda$). Being inductively reactive, it reflects RF forward.
- Driven Element (Center): Resonant dipole ($0.470 lambda$ to $0.475 lambda$) connected directly to the transmitter coaxial feedline.
- Director (Front): Cut approximately 5% shorter than the driven element ($0.440 lambda$ to $0.450 lambda$). Being capacitively reactive, it pulls and concentrates the electromagnetic wave forward.
Element Diameter & End-Effect Corrections
Thicker tubing decreases the antenna's length-to-diameter ratio ($L/d$), increasing capacitive end-effect and requiring physical shortening of elements to maintain exact electrical resonance:
Velocity Factor (K): K ≈ 0.95 to 0.97 based on tubing diameter
Boom Length: L_boom ≈ 0.35 λ to 0.40 λ for optimal 3-element gain
Frequently Asked Questions
What is a Gamma Match and why is it so popular on Yagis?
A Gamma match allows mounting the driven element as a single continuous tube bolted solidly to the metal boom without cutting it in half or insulating it. A small parallel rod and series variable capacitor transform the 20-25 ohm antenna impedance up to a perfect 50 ohm match.
Should I mount the elements vertically or horizontally?
For FM repeater work and simplex mobile communication, mount elements vertically (vertical polarization matches mobile whips). For weak-signal SSB/CW DXing and satellite work, mount elements horizontally to match standard horizontal DX arrays.
Can I add a 4th or 5th element to increase gain?
Yes! Adding more directors increases gain by approximately 1 dB for every doubling of boom length. A 5-element Yagi achieves ~10.5 dBi, but requires a boom more than twice as long.