In order to generate circular polarization in a crossed-yagi, a 90° phase delay is required between the horizontal and the vertical antenna. In practice, this is achieved either by making a mechanical shift of lambda/4 or by using phasing stubs. However, some cots antenna have a mechanical plane offset different than the lambda/4. Indeed in my case, I have a 70cm 2x19 elements antenna from Tonna that I want to set up for satellite operations. To achieve right-hand circular polarization, a phasing harness was purchased http://www.wimo.de/download/1808xx.pdf.
In the antenna datasheet, a mechanical offset of 200mm is specified. When consulting other forums and by using online phasing calculators, an extra length of -18.83 mm is needed (see screenshot). On the other hand, the phasing calculations provided in the harness datasheet are totally different.
Can someone please give me a clue here? I would reaaaaally appreciate it. I'm really lost.