[AFMUG] Spacial Diversity - helps how much?

[Adam Moffett]

There are a couple of products out there selling 4x4 MIMO (Telrad is 
one, but there are others).

In Telrad's case, two of the chains have a time offset from the other 
two, so you get two chains on each of two polarities.  Their default 
antenna is a single sector antenna with 4 N-connectors on it, so there's 
no significant spacial diversity.  In the past it's been suggested that 
we use two dual pol sector antennas and space them 3 feet apart to get 
spacial diversity.

When I asked why they do the single antenna, a source at Telrad told me 
that spacial diversity "only helps a little".  The party selling us the 
two panels considers it to add 6db when they run coverage projections.  
I suspect any gain from spacial diversity is going to depend on a lot of 
circumstances and I doubt it could be as simple as adding 6db.

I'm wondering if anyone here has any opinions on the topic?  Maybe even 
facts :)

(I'm sort of eyeballing a certain guy in Utah who designs antennas and 
isn't trying to sell me anything.)