Example Data Table
| Frequency | Elements | Boom | Efficiency | VSWR | Expected Use |
|---|---|---|---|---|---|
| 144 MHz | 5 | 2.2 m | 85% | 1.5 | VHF weak signal work |
| 432 MHz | 9 | 1.8 m | 88% | 1.4 | UHF directional link |
| 28 MHz | 3 | 4.5 m | 80% | 1.8 | HF beam planning |
Formula Used
Wavelength: λ = c / f
Boom in wavelengths: boom λ = boom length / λ
Empirical raw gain: Graw = 4.8 + 10 log10(elements − 1) + 3.2 log10(1 + 2.8 × boom λ)
Efficiency loss: Leff = −10 log10(efficiency / 100)
Reflection coefficient: Γ = (VSWR − 1) / (VSWR + 1)
Mismatch loss: Lm = −10 log10(1 − Γ²)
Total loss: Ltotal = Leff + feed loss + connector loss + extra loss + mismatch loss
Net gain: Gnet = Graw − Ltotal
dBd conversion: GdBd = GdBi − 2.15
EIRP: EIRP = transmitter watts × 10^(Gnet dBi / 10)
How To Use This Calculator
- Enter the operating frequency and select the correct unit.
- Add the total Yagi element count, including reflector and driven element.
- Enter boom length with the matching length unit.
- Add antenna efficiency, VSWR, feed line loss, and connector loss.
- Adjust element length factors when using a custom design style.
- Press the calculate button to view gain, beamwidth, wavelength, and EIRP.
- Use the CSV or PDF option to save the result.
Yagi Gain Planning
A Yagi antenna is a directional array. It uses a driven element, one reflector, and one or more directors. The driven element accepts power from the feed line. The reflector pushes more energy forward. Directors guide the wave toward the main lobe. This calculator gives a practical gain estimate for early design work.
Why Gain Matters
Gain shows how strongly the antenna focuses energy in one direction. Higher gain can improve link margin, receiver sensitivity, and usable range. It can also narrow the beam. A narrow beam needs better aiming. That is useful for point to point links, weak signal work, and distant repeaters. It is less ideal when wide coverage is required.
Important Design Inputs
Frequency sets the wavelength. Wavelength then controls element length and spacing. Element count affects gain, but extra elements give smaller returns after the first few directors. Boom length is also important. A long boom usually supports better directivity. Efficiency, feed loss, connector loss, and mismatch loss reduce the final realized gain.
Understanding The Estimate
The calculator uses an empirical model. It is not a full electromagnetic simulation. It treats element count and boom length as the main directivity drivers. It then subtracts real system losses. The result is useful for comparison, planning, and quick checking. Final antennas should still be tuned with an analyzer, field strength meter, or trusted modeling software.
Practical Tuning Notes
Keep the reflector slightly longer than the driven element. Keep directors slightly shorter. Typical spacing ranges from 0.15 to 0.25 wavelength. Small changes can strongly affect impedance and front to back ratio. Measure carefully before cutting. Leave a little extra length for trimming. Use low loss coax when the run is long. Weatherproof connectors and baluns. Poor feed details can waste more signal than another director adds.
Using Results Wisely
Compare net gain, not only raw gain. A high gain antenna with heavy cable loss may perform worse than a smaller antenna with better feed line. Check beamwidth before mounting. A very sharp pattern can miss the target if the mast twists. Use the output as a design guide, then verify the real antenna outdoors.
Record each test, because repeatable notes make improvements easier later.
FAQs
What is Yagi antenna gain?
Yagi antenna gain estimates how much the antenna focuses energy in one direction compared with a reference antenna. It is usually shown in dBi or dBd.
Is this calculator a full antenna simulator?
No. It uses practical empirical equations. It is best for planning, comparison, and quick estimates. Final designs should be verified with real measurements or modeling software.
Why does boom length affect gain?
A longer boom allows element spacing that can improve directivity. It can narrow the beam and increase forward gain when the design is tuned well.
What is the difference between dBi and dBd?
dBi compares gain with an isotropic radiator. dBd compares gain with a half-wave dipole. A dBd value is about 2.15 dB lower than dBi.
How does VSWR reduce performance?
High VSWR means more reflected power at the feed point. The calculator converts VSWR into mismatch loss and subtracts it from estimated antenna gain.
Should I enter feed line loss?
Yes. Feed line loss can greatly reduce real performance. Long coax runs and high frequencies often create noticeable loss before power reaches the antenna.
Can I use this for UHF and VHF antennas?
Yes. Enter the frequency in the correct unit. The calculator adjusts wavelength, boom ratio, element lengths, estimated gain, and beamwidth automatically.
Why are element lengths only estimates?
Real element lengths depend on tubing diameter, mounting style, nearby objects, matching networks, and construction details. Use these lengths as starting values.