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Calculators / Yagi Antenna
Yagi-Uda Antenna
Calculator
Calculate reflector length, driver length, director lengths, element spacing, and boom length for a Yagi-Uda antenna. Based on the NBS Technical Note 688 (Viezbicke) optimised tables — the industry standard reference for Yagi design.
Reflector
Driven Element
Directors
⚙ Yagi-Uda Design Engine
λ = — m in free space
Affects element length via d/λ correction
More elements → higher gain, longer boom
Advanced Parameters
mm
Boom correction shortens element lengths
NBS TN-688 Viezbicke optimised design
Folded dipole: use 4:1 balun for 75 Ω coax
Bare metal ≈ 0.95, insulated ≈ 0.85–0.93
Element Dimensions Table
| # | Element | Length | Half-Length | Spacing from Refl. | Position on Boom |
|---|---|---|---|---|---|
| Enter values above to generate table | |||||
Calculated Results
Boom Length
—m
Reflector (Lrefl)—
Driver (Ldrive)—
Director 1—
Last Director—
Free-space λ—
Element spacing—
Estimated Gain—
Front-to-Back Ratio—
3 dB Beamwidth (E)—
Input Impedance—
Number of Elements—
Enter values above to calculate.
📖 Design Theory
A Yagi-Uda antenna uses a single driven element (dipole) plus parasitic elements — one reflector behind the driver and one or more directors in front — to create a highly directive beam.
Reflector Length
Lrefl ≈ 0.5λ × k × 1.05
≈ 5% longer than driven element. Spaced 0.2λ behind driver.
Driven Element
Ldrive = 0.5λ × k × C(d/λ)
Half-wave dipole, shortened by d/λ correction factor C.
Directors
Ldir,n ≈ 0.5λ × k × 0.89–0.93
3–5% shorter than driven element each. Spaced 0.25–0.35λ apart.
Gain scales approximately as +1 dB per added director for well-designed arrays. The NBS TN-688 tables give the globally optimised spacings for each element count.
📡 Radiation Pattern Viewer
Live Simulation
|
◉ Pattern updates with element count
Plane
Elements
5
313
Boom Length
1.5 λ
E-Plane Pattern
3D Beam Pattern
ℹ
Design Insights
Enter frequency and select element count to see live design insights.
Common Applications
Amateur Radio (VHF/UHF)
2 m (144 MHz) and 70 cm (432 MHz) Yagi arrays for weak-signal and EME (moonbounce) work.
TV Aerial Reception
UHF Yagi arrays for DVB-T terrestrial television reception — the most common Yagi application.
Point-to-Point Links
Long-range WiFi (2.4/5 GHz) and ISM-band directional links between buildings.
Satellite Tracking
Cross-Yagi (dual-polarisation) arrays for LEO satellite communication and weather imagery.
How to use this Yagi antenna calculator
This calculator gives a practical starting geometry for a Yagi-Uda antenna. Enter the design frequency, select an element count, then use the calculated dimensions as a build sheet for the reflector, driven element, directors, spacing, and boom. It is useful for VHF, UHF, and directional link projects where a compact, forward-focused antenna is needed.
- Set the operating frequency. Use the centre of the band you want to cover. A narrow-band Yagi is normally tuned around the frequency that matters most.
- Choose the element count. More directors can increase directivity and gain, but they also make the boom longer and construction more critical.
- Review the dimensions table. Cut elements slightly long when practical, then trim and match during measurement rather than assuming a first build is final.
- Validate the finished antenna. Feed method, boom material, mounting hardware, nearby metal, cable routing, and installation height can all affect resonance and impedance.
Use calculated dimensions as a starting point
Element length and spacing
Yagi performance depends on the relationship between every parasitic element, not only on the driven-element length. Keep spacing accurate and make the physical build repeatable before making small tuning changes.
Matching and measurement
The calculator estimates geometry, not a guaranteed final SWR. Confirm the feed-point impedance and return loss with appropriate measurement equipment, then adjust the matching network or driven element as required.
Yagi antenna calculator FAQ
Are these dimensions ready to build without adjustment?
They are a well-informed starting point. Final dimensions can change with element diameter, insulation, a conductive boom, mounting clamps, the feed arrangement, and the installed environment. Measure the completed antenna before permanent installation.
Why is the reflector longer than the driven element?
The reflector is a parasitic element placed behind the driven element. Its length and spacing help create the rear suppression and forward directivity associated with a Yagi-Uda array.
How many elements should a Yagi antenna have?
Choose the shortest boom that meets your gain and beamwidth needs. A three-element design is often a practical starting point, while longer arrays suit weak-signal, satellite, and fixed directional applications when mechanical accuracy is available.
Can I use the calculator for 2.4 GHz or 5 GHz links?
Yes, but small dimensional errors become more significant as frequency rises. Use accurate materials, connectors, and measurement methods, and consider substrate or enclosure effects when the antenna is integrated with a PCB or radio enclosure.
Related RF tools
Use these calculators alongside the Yagi design workflow for wavelength checks, feed-element starting dimensions, gain estimates, and path planning.
Antenna Length Calculator
Dipole Antenna Calculator
Antenna Gain Calculator
Friis Transmission Calculator
Wavelength Calculator
All Antenna Calculators
Technical reference: NBS Technical Note 688, Yagi Antenna Design. Use the calculator as a design aid and verify a fabricated antenna with appropriate RF measurement methods.
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Learn practical principles for better RF circuits, PCB layouts, simulations, measurements, and troubleshooting.