>
> This could explain why Yuri's XJ3ZZ/1 antenna provided superior
> fading characteristics even though it was an ostensibly linearly
> polarized antenna. In free space, a corner-fed loop will give
> linear "tilted" polarization (not circular), but when you put it over
> ground, the reflections might provide the differential phase shift
> between the horizontally and vertically polarized field components
> such that the resultant polarization characteristics were elliptical
> or circular (at least at some TOAs). I dunno if TA keeps track
> of phase. If so, one could probably simulate all this.
>
> 73 de Mike, W4EF
I don't know about TA, but HFTA, in the latest ARRL antenna book, says that
it only handles horizontally polarized antennas, which makes me think that
it doesn't deal with polarization at all, but just assumes Hpol everywhere
all the time. Given that most "real" antennas have some cross pol component
(it would be an ordeal to try and design an antenna with a cross pol of less
than, say, 20 dB), this is probably one bound on the performance of such
modeling tools. On the other hand, if your antenna has a cross pol of -10
to -15dB, the "wrong sense" is down by 90-95%, so even if the model is
inaccurate, the contribution will be small.
And, of course, the polarization response of an antenna "off axis" is even
funkier than the on-axis response, with higher gain antennae being even more
subject to this than others. That superduper 1degree beamwidth gazillion
element yagi might have a very odd response in the far field, once the
terrain and polarization effects get in the picture.
Jim W6RMK
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|