Yagi Stacking Distance Calculator

Calculator Inputs

Frequency

MHz

Beamwidth in chosen plane

deg

Stacking plane

Spacing factor

Number of antennas

Single antenna gain

dBi

Feedline velocity factor

Approximate boom length

m

Extra mechanical clearance

m

Project notes

Example Data Table

Band	Frequency	Beamwidth	Factor	Approximate spacing	Use case
VHF	144.2 MHz	48°	1.00	2.46 m	Two long boom antennas
UHF	432.1 MHz	42°	0.95	0.92 m	Compact tower stack
6 meter	50.15 MHz	55°	1.05	6.80 m	Wide support frame

Formula Used

Wavelength: λ = c / f. The value c is 299,792,458 meters per second. Frequency must be entered in hertz after conversion from MHz.

Beamwidth spacing estimate: D = λ / [2 × sin(BW / 2)]. BW is the half power beamwidth in the chosen stacking plane.

Adjusted spacing: Final D = D × spacing factor. Use 1.00 for the base estimate, lower values for compact systems, and higher values for open arrays.

Array gain estimate: Gain = single antenna gain + 10 log10(number of antennas) − planning loss.

How To Use This Calculator

Enter the operating frequency in MHz.
Enter the antenna beamwidth for the plane being stacked.
Select the stacking style that matches your layout.
Set the spacing factor. Start with 1.00 for a normal estimate.
Add gain, feedline velocity factor, boom length, and clearance values.
Press calculate. Review the result above the form.
Download CSV or PDF results for field records.

Yagi Stacking Distance Guide

Stacking two or more Yagi antennas can increase gain. It can also narrow the useful beam. The correct center to center spacing matters. Too little spacing causes strong coupling. Too much spacing can create side lobes and weak nulls. This calculator gives a practical first estimate for field planning.

What The Distance Means

Stacking distance is measured between antenna centers. For a side by side stack, measure between boom center lines. For an over under stack, measure between the electrical centers of the antennas. Use the same plane as the selected beamwidth. Horizontal stacking normally uses horizontal beamwidth. Vertical stacking normally uses vertical beamwidth.

Why Beamwidth Is Useful

A narrow beam antenna usually needs more spacing. A wide beam antenna usually needs less spacing. The calculator uses the half power beamwidth method. It converts frequency into wavelength. Then it estimates the spacing that lets the stacked patterns combine with useful forward gain.

Practical Adjustment

The spacing factor lets you tune the result. A value below one gives a compact array. It may reduce gain slightly. A value above one increases spacing. It may sharpen the pattern. It may also raise side lobe risk. Field testing is still important, because tower height, nearby metal, feed balance, and antenna design affect real results.

Gain And Feed Notes

The gain estimate is theoretical. Two identical antennas can add about three dB before losses. Four antennas can add about six dB before losses. The tool subtracts a small planning loss when spacing is compact or stretched. It also gives quarter wave and half wave feedline lengths using the velocity factor. Use these as cutting estimates, then trim with instruments.

Good Installation Practice

Keep both antennas aimed exactly the same way. Use equal feedline lengths when required. Support the boom and mast firmly. Leave enough mechanical clearance for wind movement. Check the pattern on air or with test gear. The calculator is best used as an engineering worksheet, not as a final replacement for antenna modeling software.

Record each trial. Compare signal reports at the same power. Watch front to back ratio, side noise, and rotor load. Small changes can improve real station performance. Always recheck all fasteners after severe weather.

FAQs

What is Yagi stacking distance?

It is the center to center distance between two or more Yagi antennas in a stack. It helps the antennas combine forward energy while controlling coupling and pattern shape.

Which beamwidth should I enter?

Enter the beamwidth from the plane you are stacking. Use horizontal beamwidth for side by side stacking. Use vertical beamwidth for over under stacking.

Is the calculated spacing final?

No. It is a planning estimate. Real antenna patterns depend on the exact Yagi design, mast, tower, feedline layout, height, and nearby metal structures.

What does the spacing factor do?

It adjusts the base spacing. Use values below one for compact arrays. Use values above one when you want wider spacing and can manage side lobes.

How much gain does stacking add?

Two equal antennas can add about three dB before losses. Four equal antennas can add about six dB before losses when phasing and spacing are correct.

Why are feedline lengths shown?

Quarter wave and half wave sections help with phasing and matching plans. They use the velocity factor, so always verify final lengths with measurement tools.

Can I use this for any band?

Yes, if you enter the correct frequency and beamwidth. The physical result grows as wavelength grows, so lower frequency arrays need larger spacing.

What happens with spacing too wide?

Very wide spacing can increase side lobes and split the main pattern. It may look strong in one direction but create unwanted reception elsewhere.