The construction principles of the Duoband-Yagis depends on the "open-sleeve"- elements. The developing of these elements are shown down. You can construct not only "open-sleeve"-radiators, it is possible to use "open-sleeve"-directors, too.

First step: A tube ("sleeve") will be pushed over the dipole for f1. You will get a second resonance on another (higher) frequency f2.

Second step: The tube ("sleeve") will be replaced by two skeleton elements nearby ("open-sleeve"). You will get a second resonance on another frequency f2, too. Adjusting length and distance are much easier than with a tube element.

Third step: You need only one skeleton element for resonance on a second frequency f2. With the length of this "open-sleeve"-element you set the frequency f2, with the distance the radiation resistance for f2.

It is possible to get a second resonance with a definend radiation resistance (impedance) with such an element. You can add more than one element for more resonances with one feedpoint.

The diameter and distance of all elements is very critical, a little difference causes severe changes in the parameters!

A special case is the combining of 145 MHz and 435 MHz, because 435 MHz is an harmonic of 145 MHz and the dipole 1 for 2 m has a 3/2-lambda-resonance on 70 cm.