Skip to content
RFrftools.io
Antenna

Yagi-Uda Antenna Design Calculator

Calculate Yagi-Uda antenna element lengths, gain, spacing, and impedance. Design directional Yagi antennas for any frequency. Free, instant results.

Loading calculator...

Formula

λ=c/f;G≈10⋅log10(0.8⋅N)+2.15dBi(c=299792458m/s)λ = c/f; G ≈ 10·log₁₀(0.8·N) + 2.15 dBi (c = 299 792 458 m/s)
λ— Wavelength (m)
f— Frequency (MHz)
N— Number of elements
G— Gain (dBi)

How It Works

Yagi antenna calculator computes element lengths, spacing, and gain for directional arrays — amateur radio operators, TV broadcast engineers, and point-to-point wireless designers use Yagis for their excellent gain-to-size ratio. The design uses one driven element (fed directly), one reflector (5% longer, spaced 0.15-0.25 lambda behind), and multiple directors (3-5% shorter, spaced 0.1-0.35 lambda ahead), per Balanis's 'Antenna Theory' (4th ed.) and the classic DL6WU design tables.

Gain scales approximately as G = 10*log10(n) + 7 dBi for n elements with optimized spacing, achieving 6 dBd (8.15 dBi) for 3 elements, 9 dBd (11.15 dBi) for 6 elements, and 12 dBd (14.15 dBi) for 10+ elements. The driven element is typically a folded dipole (300 ohms) transformed to 50 ohms via 4:1 balun, or a split dipole with direct feed. Front-to-back ratio of 15-25 dB reduces interference from the rear.

Bandwidth is inversely related to element count: a 3-element Yagi covers approximately 5% bandwidth with VSWR < 2:1, while a 12-element design may have only 2% bandwidth. The log-periodic dipole array (LPDA) provides 3:1 or wider bandwidth at the cost of 3-6 dB lower gain than a Yagi of similar boom length. Yagi design requires careful optimization of element lengths and spacings — published designs (DL6WU, NBS, VK3AUU) provide proven starting points.

Worked Example

Problem: Design a 5-element Yagi for 145 MHz (2-meter amateur band) with direct 50-ohm coax feed.

Design using DL6WU optimized dimensions:

  1. Wavelength at 145 MHz: lambda = 300/145 = 2.069 m
Element lengths (DL6WU design):
  1. Reflector: 0.495 * lambda = 1.024 m
  2. Driven element: 0.473 * lambda = 0.978 m (split dipole)
  3. Director 1: 0.440 * lambda = 0.910 m
  4. Director 2: 0.435 * lambda = 0.900 m
  5. Director 3: 0.430 * lambda = 0.890 m
Element spacing from reflector:
  1. Reflector to driven: 0.20 * lambda = 414 mm
  2. Driven to D1: 0.20 * lambda = 414 mm (cumulative: 828 mm)
  3. D1 to D2: 0.25 * lambda = 517 mm (cumulative: 1345 mm)
  4. D2 to D3: 0.25 * lambda = 517 mm (cumulative: 1862 mm)
  5. Total boom length: 1.86 m (0.9 lambda)
Feed arrangement for 50 ohms:
  1. Split dipole impedance at resonance: approximately 20-25 ohms (lowered by parasitic coupling)
  2. Use T-match or gamma match to transform to 50 ohms
  3. Alternative: folded dipole driven element (300 ohms) with 4:1 balun
Expected performance (per NEC simulation):
  1. Gain: 10.5 dBi (8.35 dBd)
  2. Front-to-back ratio: 20 dB
  3. 3-dB beamwidth: 52 degrees E-plane, 62 degrees H-plane
  4. Bandwidth (VSWR < 1.5): 143-147 MHz (2.8%)
Construction notes:
  1. Use 10-12 mm aluminum tubing for elements
  2. Mount elements through insulated boom or use element-to-boom correction (subtract 1-2% from element length for conductive boom)
  3. Seal all joints against moisture for outdoor durability

Practical Tips

  • ✓Start with proven designs (DL6WU, NBS, VK3AUU) rather than calculating from scratch — these have been optimized through simulation and field testing over decades
  • ✓For receiving applications (SDR, weak-signal), longer Yagis with more directors provide better signal-to-noise despite narrower bandwidth; for transmitting, ensure full VSWR bandwidth coverage
  • ✓Use 4NEC2 or EZNEC modeling software to optimize element dimensions for your specific materials (tube diameter, boom style) before construction

Common Mistakes

  • ✗Using theoretical dipole length (lambda/2) for driven element — parasitic coupling from reflector and directors lowers resonant length by 5-10%; always use published optimized designs or NEC simulation
  • ✗Incorrect element spacing — spacing is more critical than length for gain; 0.1 lambda error in director spacing can reduce gain by 1-2 dB and shift resonant frequency 5%
  • ✗Neglecting boom-to-element correction — conductive boom passing through elements acts as a parallel inductance, requiring 1-3% length reduction depending on boom diameter; insulated mounting eliminates this effect
  • ✗Assuming equal director lengths — optimal designs use tapered director lengths, each progressively shorter; equal-length directors reduce gain by 1-2 dB versus optimized taper

Frequently Asked Questions

Gain scales with element count per Balanis analysis: 2 elements: 5-6 dBi (reflector + driven only). 3 elements: 7-8 dBi. 5 elements: 10-11 dBi. 8 elements: 12-13 dBi. 12 elements: 14-15 dBi. 20+ elements: 16-17 dBi (practical limit due to losses). Gain increases approximately 1 dB per added director until diminishing returns around 10-12 elements. Boom length (not element count alone) determines gain: 1 lambda boom approximately equals 11 dBi; 2 lambda boom approximately equals 14 dBi.
A fixed Yagi operates over narrow bandwidth (2-5% typical). For different bands: (1) Build separate Yagis for each band. (2) Use interlaced Yagis on common boom (elements for different bands interleaved, with care to avoid interaction). (3) Use log-periodic dipole array (LPDA) for wide bandwidth (3:1 ratio) at cost of 3-6 dB less gain. (4) Active antenna selection via relay. Yagi elements scale inversely with frequency: a 144 MHz Yagi scaled to 432 MHz uses 1/3 dimensions but same electrical design.
Yes — Yagis excel at point-to-point and weak-signal work due to high gain and directivity. Applications: Amateur radio EME (Earth-Moon-Earth): stacked 12+ element Yagis providing 20+ dBi. Amateur satellite: 8-12 element Yagis at 145/435 MHz with Az-El rotator. Point-to-point WiFi bridges: 2.4/5.8 GHz Yagis reaching 10+ km. TV reception: 10-15 element UHF Yagis for distant stations. Gain translates to range: 10 dBi Yagi versus dipole provides 10 dB link improvement, equivalent to 3.2x range increase in free space.
Element lengths as fraction of wavelength (lambda = c/f): Reflector: 0.495*lambda (slightly longer than resonance). Driven element: 0.473*lambda (resonant at slightly higher frequency). Directors: 0.440-0.430*lambda (tapered shorter toward front). Spacings: Reflector to driven: 0.15-0.25*lambda. Driven to D1: 0.10-0.20*lambda. D_n to D_(n+1): 0.20-0.35*lambda, often increasing toward front. These ratios are starting points — use published optimized designs (DL6WU, NBS) or NEC modeling for best results. Element diameter affects length: thicker elements are shorter.
Yagi: All elements coupled parasitically to single driven element; narrow bandwidth (2-5%); highest gain per boom length; requires retuning for different frequencies. LPDA: All elements active (connected to feedline via phased transmission line); wide bandwidth (3:1 to 10:1); 3-6 dB less gain than same-length Yagi; no retuning needed. Choose Yagi for maximum gain on single frequency (amateur, point-to-point). Choose LPDA for wide bandwidth with moderate gain (TV reception across UHF band, wideband monitoring, EMC testing).

Shop Components

As an Amazon Associate we earn from qualifying purchases.

SMA Right-Angle Connectors

Edge-mount and right-angle SMA connectors for antenna feeds

Amazon →

RTL-SDR Dongle

Wideband SDR receiver for antenna and signal experiments

Amazon →

Magnet Wire (22 AWG)

Enameled copper wire for winding custom antennas and coils

Amazon →

Related Calculators

Antenna

Dipole Antenna

Calculate dipole antenna length for any frequency — enter MHz, get half-wave and quarter-wave dimensions in mm. Includes gain (2.15 dBi), radiation resistance (73 Ω), and 50 Ω VSWR. Supports velocity factor for insulated wire.

Antenna

EIRP / ERP

Calculate EIRP and ERP from transmit power, cable loss, and antenna gain. Check FCC Part 15 and ETSI regulatory compliance margins. Free, instant results.

Antenna

Patch Antenna

Calculate rectangular microstrip patch antenna dimensions (width, length) using the Transmission Line Model. Outputs effective dielectric constant, edge-feed impedance, and nominal gain for common substrates like FR4 and Rogers.

Antenna

Beamwidth

Calculate antenna 3 dB beamwidth, gain from aperture, and effective area. Determine HPBW for dish, horn, and aperture antennas. Free, instant results.