Some months ago, Bent OZ1CT asked me for a X-pol LFA (two LFA Yagis, one in the vertical plane, one in the horizontal plane on the same boom). Whenever I have received such requests I have been reluctant to work on them due to the many complexities involved in not just getting the model working but getting it working correctly and as model.

There are designs from many well-known designers and commercial entities around today but none that I have seen get it right in the electromagnetic design or mechanical construction and this in part is due to the lack of understanding of off-sets (elements) and the impact certain materials will have upon this antenna and without doubt, this is the main reason many hams are not 100% happy with their X-pol arrays.

I have spent much time modeling X-pol array in EXACTLY the arrangement they will be in once built, established the issues and made every effort to avoid and reduce any distortions. The details and result fo these findings will be published within the pages of DUBUS a little later this year but for now, take a look at one of the first ever X-pol LFA Yagis at OZ1CT.

The X-pol 2m LFA Yagi at OZ1CT

Despite my recommendations against it, Bent decided to boxes over each feed point and therefore, there will be some negative impact upon feed point impedance. There are other ways to seal your feed point without degrading your antenna! However, Bent has still achieved good results in SWR within almost near perfect results in both planes. See the SWR plots from both planes below:

SWR in the first plane

SWR in the second plane

IZ8DWF recently built one of my 4/6m dual-banders and while he did not use good insulators (which would impact performance) he did comment on how surprised he was at just how close my designs where to the software model when built.

If you are building a Yagi this year, take care with materials and make sure you will not make the same mistakes so many self-builders to through being ill-advised. Even some of the most popular, well-known designers get it wrong as far as mechanical construction is concerned. If you are 'OK' with your antenna just being somewhere close and 'OK' with 20dB return loss, you will not have to read anything further on this site relating to material correction! If you just don't want to build then no problem, take a look at the InnovAntennas website as a full range of X-pol LFAs will be launched in February 2012.

Happy New Year to you all!