Example Data Table
| Band Use | Frequency MHz | Elements | Reflector Factor | Driven Factor | First Director Factor |
|---|---|---|---|---|---|
| VHF field antenna | 144.000 | 5 | 0.505 | 0.475 | 0.465 |
| UHF compact antenna | 433.000 | 7 | 0.500 | 0.470 | 0.455 |
| Long boom build | 50.200 | 6 | 0.510 | 0.480 | 0.468 |
Formula Used
Wavelength is calculated as λ = 299792458 / frequency in hertz. The reflector length uses λ × reflector factor. The driven element uses λ × driven factor. Each director uses λ × director factor. A taper value shortens later directors.
Element position is calculated along the boom. The reflector starts at zero. The driven element is placed after reflector spacing. Directors are placed after the selected director spacings. Diameter and mount corrections are subtracted from element length.
Gain, beamwidth, front to back ratio, and feed impedance are estimates. They help with early planning. Final performance depends on nearby metal, element material, boom mounting, height, feed method, and tuning.
How To Use This Calculator
Enter the design frequency first. Choose the total number of elements. Select your preferred output unit. Adjust element factors only when you know your design goal. Use the default values for a normal starting layout.
Press the calculate button. The result appears above the form. Review total element lengths and half lengths. Mark each boom position from the reflector end. Export the data when you are ready to build.
Yagi Uda Antenna Design Guide
Directional Antenna Basics
A Yagi Uda antenna is a focused radio antenna. It uses several parallel elements on one boom. The driven element connects to the feed line. The reflector sits behind it. Directors sit in front of it. This arrangement pushes more signal forward. It also reduces signal from the rear. That makes the design useful for weak signals.
Why Frequency Matters
Every dimension starts with wavelength. Higher frequency means shorter wavelength. Shorter wavelength means smaller elements and spacing. Lower frequency needs longer parts. This calculator converts frequency into wavelength. It then applies practical length factors. These factors give a strong first layout. Final tuning should still use field checks.
Element Roles
The reflector is usually the longest element. It reflects energy toward the directors. The driven element is slightly shorter. It sets the main feed point. Directors are shorter than the driven element. Each extra director can add gain. More directors also narrow the beam. Very long designs need careful construction.
Spacing Choices
Spacing changes gain, impedance, and pattern shape. Wide spacing may improve bandwidth. Tight spacing can raise interaction. The first director often needs special spacing. Later directors may use a regular spacing. The calculator lets you adjust both. Boom length includes an allowance. This helps with clamps and end space.
Practical Building Notes
Cut every element a little long. Mount the antenna away from walls. Keep the boom straight and firm. Use the same measuring reference for all positions. Check the feed match before final mounting. Trim small amounts during tuning. Record each change after testing. Good notes make later repairs easier.
Using The Results
The table gives total element length. It also gives half length. Half length is useful for split driven elements. Boom position shows where each element center sits. Export the table for workshop use. The PDF option is best for printing. The CSV option is best for spreadsheets. Use both before cutting costly material.
FAQs
1. What does this Yagi Uda antenna calculator do?
It estimates element lengths, boom positions, spacing, gain, beamwidth, front back ratio, and feed impedance from your selected frequency and design options.
2. Can I use these dimensions without tuning?
Use them as a strong starting point. Real antennas need tuning because mounting, nearby metal, material size, and feed method can shift resonance.
3. Why is the reflector longer than the driven element?
The reflector is longer so it acts slightly below resonance. This helps push energy toward the directors and improves forward direction.
4. Why are directors shorter?
Directors are shorter so they act slightly above resonance. They guide energy forward and help create the narrow directional beam.
5. What does director taper mean?
Director taper shortens each later director by a small factor. It can improve pattern control and helps long boom designs stay practical.
6. What unit should I choose?
Choose the unit used by your tools. Millimeters suit small antennas. Centimeters work well for VHF builds. Inches may suit imperial workshops.
7. Is the estimated gain exact?
No. Gain is an approximation for planning. Accurate gain needs modeling software, careful build quality, open-area testing, and proper measurement equipment.
8. What should I do before cutting metal?
Check the frequency, units, and element count. Print the result, mark the boom carefully, and cut elements slightly long for tuning.