[TowerTalk] Isolated Mode Antenna Technology

[jimlux]

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)
> 
> <http://www.rfdesignline.com/howto/showArticle.jhtml;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.