# Spacing between elements on a Yagi antenna

Does anyone know what the spacing between elements on a beam antenna should be? I built a 146 MHz 3 element beam following instructions, and the spacing was 16" between the driven element and the reflector and 20" between the driven element and the director. I was just wondering how you determine the proper spacing between elements; is there any set formula you use to determine boom length, element spacing, etc. that you can use to design a yagi? If anyone can tell me, I would really appreciate it.

• There are many kinds of beam antennas. Do you mean a Yagi antenna (the most common kind) or some other type? Commented May 14, 2014 at 4:21
• You can use the beam antenna calculator at csgnetwork.com/antennae3ycalc.html for a quick check on your math. Commented May 14, 2014 at 4:42
• Yes, I am talking about a yagi, I probably should have stated that in my question. @ghendricks Thanks for the site, I will have to check it out. Commented May 14, 2014 at 12:41
• @ghendricks that site doesn't seem to be working. Maybe it doesn't like my computer. Commented May 15, 2014 at 15:24

It would be nice to think that there is simple formula or algorithm that one could plug the frequency and desired gain into, and out would come the required element spacings.

The reality is that the math is difficult - requiring the solution of many simultaneous equations - and the results may still not absolutely mirror reality due to variations in materials.

Most Yagi-Uda designs are based on empirical methods and often use pre-tested models such as those by the NIST and DL6WU.

The spacing of the reflector and the first director are usually the most critical. Multiple directors usually end up with around 0.4 wavelength spacing. Small amounts of improvement in gain can be obtained by playing with the spacing of the directors - however, it is generally not worth the effort.

If you can obtain a copy of the ARRL Antenna Book, chapter 18 will likely be helpful.

Additionally, the following resources may also be informative:

K7MEM VHF/UHF Yagi Design Help

There are a few more that I would like to include, but I do not have enough reputation points.

• Commented May 19, 2014 at 2:26
• Thanks for the information, I will definately check it out. Commented May 22, 2014 at 0:55

The spacing of of the driven element from the reflector of a Yagi antenna is $$0.19 \cdot \text{wavelength}$$ then, the spacing of the driven element from the director element is $$0.17 \cdot \text{wavelength}$$

If you are like me and don't have an antenna range, high tech test equipment or the engineering expertise to delve into modifying computerized designs based on materials on hand, simply try .31-wavelength spacing between each of the elements of your homebrew yagi with the the usual element lengths derived from other designs or from your own knowledge about gain vs bandwidth! Or, if you are obsessed with squeezing out some fraction of a dB, just get a copy of the owner's manual of a commercially made yagi of your choice and use their lengths and spacings and tubing diameters for a start! I did and ended up with simple .31-wavelength element spacing with commercial element lengths and whatever tubing I had, with gamma matches and am happy with my "sort-of homebrewed" 4-element 50, 10-element 144 and 10-element 432 mHz yagis!

GL & 73, WA4A