Calculates element lengths for three antenna types from operating frequency, velocity factor and wire/tube diameter: a quarter-wave ground plane vertical with radials (including radial angle for a target feed impedance), a half-wave dipole, and a multi-element Yagi (reflector, driven element and directors with spacing, boom length and estimated gain). Switch between antenna types using the tabs below.
Input Parameters
Design Formulas
λ = c / f
where c = 299,792,458 m/s (speed of light), f = frequency in Hz
λ_actual = λ × Velocity Factor
k = 1 - (d/λ) × 0.06
where d = wire diameter, λ = actual wavelength
Thicker elements are electrically longer, requiring shorter physical length
Minimum correction factor: 0.95
A = (λ_actual × 0.25 × k) × 1000
Result in millimeters, with diameter correction applied
B = (λ_actual × 0.28 × k) × 1000
Radials are 12% longer than vertical element. Result in millimeters, with diameter correction applied.
α ≈ min((Z₀ - 36) × 3.214, 60°)
where Z₀ = desired impedance (Ω), α = radial angle downward from horizontal
Common values:
• 36Ω: 0° (horizontal radials)
• 50Ω: ~45° down from horizontal
• 75Ω: ~60° down from horizontal (capped)
Minimum: 4 radials (90° spacing)
Recommended: 16-32 radials for optimal performance
Input Parameters
Design Formulas
λ = c / f
where c = 299,792,458 m/s (speed of light), f = frequency in Hz
λ_actual = λ × Velocity Factor
k = 1 - (d/λ) × 0.06
where d = wire diameter, λ = actual wavelength
Thicker elements are electrically longer, requiring shorter physical length
Minimum correction factor: 0.95
L_total = (λ_actual × 0.5 × k) × 1000
Half-wavelength dipole, result in millimeters
L_half = (λ_actual × 0.25 × k) × 1000
Each element from center feed point, result in millimeters
A half-wave dipole in free space: ~73Ω
Over ground (at λ/2 height): ~50-75Ω depending on height
Use 1:1 balun for coaxial cable connection
Input Parameters
Design Formulas (DL6WU Method)
λ = c / f
where c = 299,792,458 m/s (speed of light), f = frequency in Hz
λ_actual = λ × Velocity Factor
k_element = 1 - (d_element/λ) × 0.06
k_boom = 1 - (d_boom/λ) × 0.03
Combined correction for element and boom diameter effects
L_reflector = (λ_actual × 0.51 × k) × 1000
Longest element, positioned behind driven element
L_driven = (λ_actual × 0.47 × k) × 1000
Feed point element, shortened dipole configuration
L_director1 = (λ_actual × 0.44 × k) × 1000
L_director2 = (λ_actual × 0.43 × k) × 1000
L_director3+ = (λ_actual × 0.42 × k) × 1000
Directors progressively shorten, positioned in front of driven element
S_reflector = 0.15 × λ_actual
S_director1 = 0.20 × λ_actual
S_directors = 0.20 × λ_actual (typical)
Spacing from driven element (reflector behind, directors in front)
L_boom = S_reflector + S_director1 + (n-1) × S_directors
where n = number of directors
Gain (dBi) ≈ 7.5 + (n × 1.1)
where n = number of directors (diminishing returns after 5-6 directors)
3-element: ~7-8 dBi, 5-element: ~10-11 dBi, 7-element: ~12-13 dBi
Typical F/B ratio: 18-25 dB (depends on reflector spacing and element tuning)
Optimum reflector spacing: 0.15-0.20λ from driven element
Simple dipole driven element: ~28-35Ω (requires matching for 50Ω coax)
Matching methods for simple dipole:
• Gamma match (most common for metal boom)
• Hairpin match (beta match)
• Direct 50Ω match with optimized element spacing
Folded dipole driven element: ~200-300Ω (requires 4:1 or 6:1 balun for 50Ω coax)
• Advantage: Higher impedance, easier to match
• Advantage: Wider bandwidth
• Disadvantage: More complex construction
• Mount antenna at least λ/2 above ground for best performance
• Use weatherproof materials (aluminum, stainless steel)
• Insulate driven element from boom
• All other elements can be grounded to boom
• Use balun at feed point to prevent common-mode currents
• Fine-tune element lengths ±5% for best SWR