On Wed, 24 Sep 2008 22:39:23 -0700 (PDT), Penang
wrote:

Specifically, my interest is in the "broadcast" type of antenna ...
trying to find a way to "extend" the range of a typical wifi
basestation using antennas alone (maybe with the help of MIMO
antennas), without "range repeaters" or whatnots.

Broadcast implies one way transmissions. Wi-Fi is bi-directional.

The common terms are "range extender" or "repeater". These normally
refer to store and forward transmitter/receivers use to extend range
by retransmitting the data. This is roughly how a MESH network
operates. There are some severe limits and compromises to using such
repeaters, none of which have anything to do with the antenna. Ask if
you need details.

My brain is now fully clogged, and I'm having difficulties digesting
all the stuffs that I've gotten.

One must suffer before enlightenment. You're doing fine.

Is there a place (a forum, a website, a tutorial, and whatnots) where
one can learn about antennas, without having one's brain clogged up,
like mine right now?

No. Brain damage is a known side effect and complication resulting
from trying to digest the entire field of antenna design all at once.
Just reading some of the posting in this newsgroup should adequately
demonstrate the extent of the damage. I suggest you approach antenna
design in the same manner as eating a loaf of bread. It's done one
slice at a time. If you try to shove the entire loaf down your throat
at once, you'll choke.

What's your suggestion / opinion on how to construct an excellent
(pair) of MIMO antenna for wifi (802.11 b/g/n) ?

I suggest you give up immediately and read about how MIMO works.
External MIMO antennas are a problem.

There are two basic types of MIMO. One is called "beam forming",
which uses an elaborate and flat array of internal antennas to
customize the antenna pattern. Major lobes are pointed in the
direction of users. Nulls are pointed in the direction of
interference. The key point is that antennas are internal and
therefore external antennas have no place to plug in.

The other type is called "spatial diversity". It uses multiple
antennas and multiple receivers to combine reflective signal paths. In
theory, each path is independent and carry an independent data stream.
Combining these paths results in enhanced speeds. Note that this form
of MIMO is all about speed, not range.

It is possible to attach external antennas to a spatial diversity type
MIMO system. However, there are limitations. You can't just install
3 directional antennas pointed in 3 different directions. Pointed in
opposing directions, the antennas will simply not pickup any
reflections. If there are any long path reflections, the delays will
probably be excessive and the data deemed useless. Attaching a single
antenna to a MIMO spatial diversity type router will function, but
only at 802.11g speeds. Without the time delayed reflections, there's
no MIMO speeds.

Anyway, I don't have any suggestions on how to construct an excellent
antenna. You haven't specified what you're trying to accomplish, what
you have to work with, what is your operating environment, and what
problem you're trying to solve. Different types of antennas are
designed to solve different problems. Without a clue as to the
problem and limitations, it's rather difficult to select a suitable
antenna.

Hint: Forget about using "N" or MIMO with external antennas. Unless
you're trying to move video, 802.11g speeds are good enough.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558