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Re: [TowerTalk] Isolated Mode Antenna Technology

To: jimlux <>,
Subject: Re: [TowerTalk] Isolated Mode Antenna Technology
From: Steve Sacco NN4X <>
Date: Sun, 20 Dec 2009 12:00:41 -0500
List-post: <">>
Jim -

Thanks for your thoughts.  I wish I had more to contribute, but being as 
I'm not an antenna designer by education or trade, I can only offer what 
my thoughts were when I posted that:

1) If you think in terms of wavelengths, typical Amateur stations are 
not all that dissimilar, especially on 160 and 80 meters.

2) Propagation can and does vary, and there are definitely times when 
you want to use an antenna providing peak at a higher/lower incoming angle.

3 As I was reading that article, my first thought was that it would be 
interesting to have, say, a Delta Loop, and be able to tap it at 
different points simultaneously, to (perhaps) take advantage of the 
different characteristics.


jimlux wrote:
> Steve Sacco NN4X wrote:
>> This seemed like an interesting concept.  I thought I'd pass it
>> along.
>> Isolated Mode Antenna Technology lets a single antenna offer the 
>> performance benefits of multiple antennas (Part 1 of 2)
>> <;jsessionid=F1SQHL23DOWTNQE1GHPCKHWATMY32JVN?articleID=222001586>
> Interesting, but I don't know that it's a big advance or 
> revolutionary, especially since they didn't give any details.
> From a ham standpoint, this solves a problem that hams don't have.
> For all these MIMO/diversity type systems, you want multiple antennas 
> that are decorrelated.  For instance, in HF, you could use a loop and 
> a monopole, because skywave fading on one generally doesn't happen on 
> the other at the same time because the polarization and pattern are 
> different.  Or you could separate your antennas by some distance.  In 
> either case, you need antennas that are not strongly coupled 
> (otherwise, they'll tend to receive the same signal)
> In a USB dongle, though, you don't have the luxury of spreading the 
> antennas out, and in fact, you want them really small.  At 2.4GHz (for 
> 802.11b/g/n) the wavelength is about 12 cm, so a straight halfwave is 
> 6cm (or bigger than the usual USB pod or bluetooth module)
> In conventional consumer gear, they make a resonant antenna smaller by 
> loading it (put it on a ceramic substrate with high epsilon) or by 
> bending it (meander line).  The latter is really no different than a 
> helically loaded shortened vertical.  1/4 wave of wire in <1/4 wave of 
> space.
> But, if you're doing MIMO, the whole thing depends on having the 
> antennas receive different signals. (so they see "different" 
> multipath) In a laptop, that's easy.. put one antenna on each side. In 
> a wireless access point, it's easy, put one antenna on each end.  But 
> in something the size of a thumb drive or a cell phone?  There's just 
> not enough room, especially if you're already shrinking things.
> So what they're claiming here and showing modeled or test data (while 
> carefully not describing the actual design), is some clever way to put 
> two antennas in the same physical space that have very different 
> patterns.  Sort of like having two crossed dipoles.

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