The purpose of the calculator is to give you the needed sizing to construct a good multi-element cubical quad antenna for amateur radio use. This calculator requires only the entry of the center of the frequency range your cubical quad antenna will be used at. Default is 10 meters 28 mhz . Change this to whatever frequency you like. Click on Calculate to display the critical antenna measurements in both inches and centimeters.
The optimum gain of any ham radio antenna with parasitic elements varies with the spacing and tuning of the antenna's elements. The QUAD ALWAYS requires manual tuning and optimization.

This calculator will get you in the ballpark, and as written will provide you with a very good cubical quad antenna. But as stated above, manual tuning and optimization will bring greater results.
The optimum front to back ratio does not match the maximum forward gain in any Yagi or Cubical Quad. The impedance of the driven element also varies with all tuning and spacing operations. The Quad antenna system must be tuned, probably several times in small increments, to its final condition before the final match between the coax and the antenna can be completed.
The antenna can be fed directly with standard coaxial cable 50ohm unbalanced, Use a 1:1 balun at the feed point . It should also be noted that for vertical polarization feed, the driven element is fed from the side of the diamond or square, and for horizontal polarization feed the driven element is fed at the bottom of the diamond or square, depending on your mounting orientation. Diamond and Square configurations result in the same forward gain.If you want to only build a 3 element beam, then only use the Reflector/Driven/Director 1 sizes and spacings. For a 4 element beam only use the Reflector/Driven/Director 1/ Director 2..... sizes and spacings. Its the same story for whatever size Cubical Quad you would like to build.